1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.rst, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_EVENTS 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <byte> or <bitmap-list> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_no_watchdog [HW,ACPI,WDT] 140 Ignore the ACPI-based watchdog interface (WDAT) and let 141 a native driver control the watchdog device instead. 142 143 acpi_rsdp= [ACPI,EFI,KEXEC] 144 Pass the RSDP address to the kernel, mostly used 145 on machines running EFI runtime service to boot the 146 second kernel for kdump. 147 148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 149 Format: To spoof as Windows 98: ="Microsoft Windows" 150 151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 152 of 2 which is mandated by ACPI 6) as the supported ACPI 153 specification revision (when using this switch, it may 154 be necessary to carry out a cold reboot _twice_ in a 155 row to make it take effect on the platform firmware). 156 157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 158 acpi_osi="string1" # add string1 159 acpi_osi="!string2" # remove string2 160 acpi_osi=!* # remove all strings 161 acpi_osi=! # disable all built-in OS vendor 162 strings 163 acpi_osi=!! # enable all built-in OS vendor 164 strings 165 acpi_osi= # disable all strings 166 167 'acpi_osi=!' can be used in combination with single or 168 multiple 'acpi_osi="string1"' to support specific OS 169 vendor string(s). Note that such command can only 170 affect the default state of the OS vendor strings, thus 171 it cannot affect the default state of the feature group 172 strings and the current state of the OS vendor strings, 173 specifying it multiple times through kernel command line 174 is meaningless. This command is useful when one do not 175 care about the state of the feature group strings which 176 should be controlled by the OSPM. 177 Examples: 178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 180 can make '_OSI("Windows 2000")' TRUE. 181 182 'acpi_osi=' cannot be used in combination with other 183 'acpi_osi=' command lines, the _OSI method will not 184 exist in the ACPI namespace. NOTE that such command can 185 only affect the _OSI support state, thus specifying it 186 multiple times through kernel command line is also 187 meaningless. 188 Examples: 189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 190 FALSE. 191 192 'acpi_osi=!*' can be used in combination with single or 193 multiple 'acpi_osi="string1"' to support specific 194 string(s). Note that such command can affect the 195 current state of both the OS vendor strings and the 196 feature group strings, thus specifying it multiple times 197 through kernel command line is meaningful. But it may 198 still not able to affect the final state of a string if 199 there are quirks related to this string. This command 200 is useful when one want to control the state of the 201 feature group strings to debug BIOS issues related to 202 the OSPM features. 203 Examples: 204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 205 '_OSI("Module Device")' FALSE. 206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 207 '_OSI("Module Device")' TRUE. 208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 209 equivalent to 210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 211 and 212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 213 they all will make '_OSI("Windows 2000")' TRUE. 214 215 acpi_pm_good [X86] 216 Override the pmtimer bug detection: force the kernel 217 to assume that this machine's pmtimer latches its value 218 and always returns good values. 219 220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 221 Format: { level | edge | high | low } 222 223 acpi_skip_timer_override [HW,ACPI] 224 Recognize and ignore IRQ0/pin2 Interrupt Override. 225 For broken nForce2 BIOS resulting in XT-PIC timer. 226 227 acpi_sleep= [HW,ACPI] Sleep options 228 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 229 s4_nohwsig, old_ordering, nonvs, 230 sci_force_enable, nobl } 231 See Documentation/power/video.rst for information on 232 s3_bios and s3_mode. 233 s3_beep is for debugging; it makes the PC's speaker beep 234 as soon as the kernel's real-mode entry point is called. 235 s4_hwsig causes the kernel to check the ACPI hardware 236 signature during resume from hibernation, and gracefully 237 refuse to resume if it has changed. This complies with 238 the ACPI specification but not with reality, since 239 Windows does not do this and many laptops do change it 240 on docking. So the default behaviour is to allow resume 241 and simply warn when the signature changes, unless the 242 s4_hwsig option is enabled. 243 s4_nohwsig prevents ACPI hardware signature from being 244 used (or even warned about) during resume. 245 old_ordering causes the ACPI 1.0 ordering of the _PTS 246 control method, with respect to putting devices into 247 low power states, to be enforced (the ACPI 2.0 ordering 248 of _PTS is used by default). 249 nonvs prevents the kernel from saving/restoring the 250 ACPI NVS memory during suspend/hibernation and resume. 251 sci_force_enable causes the kernel to set SCI_EN directly 252 on resume from S1/S3 (which is against the ACPI spec, 253 but some broken systems don't work without it). 254 nobl causes the internal blacklist of systems known to 255 behave incorrectly in some ways with respect to system 256 suspend and resume to be ignored (use wisely). 257 258 acpi_use_timer_override [HW,ACPI] 259 Use timer override. For some broken Nvidia NF5 boards 260 that require a timer override, but don't have HPET 261 262 add_efi_memmap [EFI; X86] Include EFI memory map in 263 kernel's map of available physical RAM. 264 265 agp= [AGP] 266 { off | try_unsupported } 267 off: disable AGP support 268 try_unsupported: try to drive unsupported chipsets 269 (may crash computer or cause data corruption) 270 271 ALSA [HW,ALSA] 272 See Documentation/sound/alsa-configuration.rst 273 274 alignment= [KNL,ARM] 275 Allow the default userspace alignment fault handler 276 behaviour to be specified. Bit 0 enables warnings, 277 bit 1 enables fixups, and bit 2 sends a segfault. 278 279 align_va_addr= [X86-64] 280 Align virtual addresses by clearing slice [14:12] when 281 allocating a VMA at process creation time. This option 282 gives you up to 3% performance improvement on AMD F15h 283 machines (where it is enabled by default) for a 284 CPU-intensive style benchmark, and it can vary highly in 285 a microbenchmark depending on workload and compiler. 286 287 32: only for 32-bit processes 288 64: only for 64-bit processes 289 on: enable for both 32- and 64-bit processes 290 off: disable for both 32- and 64-bit processes 291 292 alloc_snapshot [FTRACE] 293 Allocate the ftrace snapshot buffer on boot up when the 294 main buffer is allocated. This is handy if debugging 295 and you need to use tracing_snapshot() on boot up, and 296 do not want to use tracing_snapshot_alloc() as it needs 297 to be done where GFP_KERNEL allocations are allowed. 298 299 allow_mismatched_32bit_el0 [ARM64] 300 Allow execve() of 32-bit applications and setting of the 301 PER_LINUX32 personality on systems where only a strict 302 subset of the CPUs support 32-bit EL0. When this 303 parameter is present, the set of CPUs supporting 32-bit 304 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 305 and hot-unplug operations may be restricted. 306 307 See Documentation/arm64/asymmetric-32bit.rst for more 308 information. 309 310 amd_iommu= [HW,X86-64] 311 Pass parameters to the AMD IOMMU driver in the system. 312 Possible values are: 313 fullflush - Deprecated, equivalent to iommu.strict=1 314 off - do not initialize any AMD IOMMU found in 315 the system 316 force_isolation - Force device isolation for all 317 devices. The IOMMU driver is not 318 allowed anymore to lift isolation 319 requirements as needed. This option 320 does not override iommu=pt 321 force_enable - Force enable the IOMMU on platforms known 322 to be buggy with IOMMU enabled. Use this 323 option with care. 324 pgtbl_v1 - Use v1 page table for DMA-API (Default). 325 pgtbl_v2 - Use v2 page table for DMA-API. 326 327 amd_iommu_dump= [HW,X86-64] 328 Enable AMD IOMMU driver option to dump the ACPI table 329 for AMD IOMMU. With this option enabled, AMD IOMMU 330 driver will print ACPI tables for AMD IOMMU during 331 IOMMU initialization. 332 333 amd_iommu_intr= [HW,X86-64] 334 Specifies one of the following AMD IOMMU interrupt 335 remapping modes: 336 legacy - Use legacy interrupt remapping mode. 337 vapic - Use virtual APIC mode, which allows IOMMU 338 to inject interrupts directly into guest. 339 This mode requires kvm-amd.avic=1. 340 (Default when IOMMU HW support is present.) 341 342 amijoy.map= [HW,JOY] Amiga joystick support 343 Map of devices attached to JOY0DAT and JOY1DAT 344 Format: <a>,<b> 345 See also Documentation/input/joydev/joystick.rst 346 347 analog.map= [HW,JOY] Analog joystick and gamepad support 348 Specifies type or capabilities of an analog joystick 349 connected to one of 16 gameports 350 Format: <type1>,<type2>,..<type16> 351 352 apc= [HW,SPARC] 353 Power management functions (SPARCstation-4/5 + deriv.) 354 Format: noidle 355 Disable APC CPU standby support. SPARCstation-Fox does 356 not play well with APC CPU idle - disable it if you have 357 APC and your system crashes randomly. 358 359 apic= [APIC,X86] Advanced Programmable Interrupt Controller 360 Change the output verbosity while booting 361 Format: { quiet (default) | verbose | debug } 362 Change the amount of debugging information output 363 when initialising the APIC and IO-APIC components. 364 For X86-32, this can also be used to specify an APIC 365 driver name. 366 Format: apic=driver_name 367 Examples: apic=bigsmp 368 369 apic_extnmi= [APIC,X86] External NMI delivery setting 370 Format: { bsp (default) | all | none } 371 bsp: External NMI is delivered only to CPU 0 372 all: External NMIs are broadcast to all CPUs as a 373 backup of CPU 0 374 none: External NMI is masked for all CPUs. This is 375 useful so that a dump capture kernel won't be 376 shot down by NMI 377 378 autoconf= [IPV6] 379 See Documentation/networking/ipv6.rst. 380 381 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 382 Limit apic dumping. The parameter defines the maximal 383 number of local apics being dumped. Also it is possible 384 to set it to "all" by meaning -- no limit here. 385 Format: { 1 (default) | 2 | ... | all }. 386 The parameter valid if only apic=debug or 387 apic=verbose is specified. 388 Example: apic=debug show_lapic=all 389 390 apm= [APM] Advanced Power Management 391 See header of arch/x86/kernel/apm_32.c. 392 393 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 394 Format: <io>,<irq>,<nodeID> 395 396 arm64.nobti [ARM64] Unconditionally disable Branch Target 397 Identification support 398 399 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 400 support 401 402 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 403 support 404 405 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 406 Extension support 407 408 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 409 Extension support 410 411 ataflop= [HW,M68k] 412 413 atarimouse= [HW,MOUSE] Atari Mouse 414 415 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 416 EzKey and similar keyboards 417 418 atkbd.reset= [HW] Reset keyboard during initialization 419 420 atkbd.set= [HW] Select keyboard code set 421 Format: <int> (2 = AT (default), 3 = PS/2) 422 423 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 424 keyboards 425 426 atkbd.softraw= [HW] Choose between synthetic and real raw mode 427 Format: <bool> (0 = real, 1 = synthetic (default)) 428 429 atkbd.softrepeat= [HW] 430 Use software keyboard repeat 431 432 audit= [KNL] Enable the audit sub-system 433 Format: { "0" | "1" | "off" | "on" } 434 0 | off - kernel audit is disabled and can not be 435 enabled until the next reboot 436 unset - kernel audit is initialized but disabled and 437 will be fully enabled by the userspace auditd. 438 1 | on - kernel audit is initialized and partially 439 enabled, storing at most audit_backlog_limit 440 messages in RAM until it is fully enabled by the 441 userspace auditd. 442 Default: unset 443 444 audit_backlog_limit= [KNL] Set the audit queue size limit. 445 Format: <int> (must be >=0) 446 Default: 64 447 448 bau= [X86_UV] Enable the BAU on SGI UV. The default 449 behavior is to disable the BAU (i.e. bau=0). 450 Format: { "0" | "1" } 451 0 - Disable the BAU. 452 1 - Enable the BAU. 453 unset - Disable the BAU. 454 455 baycom_epp= [HW,AX25] 456 Format: <io>,<mode> 457 458 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 459 Format: <io>,<mode> 460 See header of drivers/net/hamradio/baycom_par.c. 461 462 baycom_ser_fdx= [HW,AX25] 463 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 464 Format: <io>,<irq>,<mode>[,<baud>] 465 See header of drivers/net/hamradio/baycom_ser_fdx.c. 466 467 baycom_ser_hdx= [HW,AX25] 468 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 469 Format: <io>,<irq>,<mode> 470 See header of drivers/net/hamradio/baycom_ser_hdx.c. 471 472 bert_disable [ACPI] 473 Disable BERT OS support on buggy BIOSes. 474 475 bgrt_disable [ACPI][X86] 476 Disable BGRT to avoid flickering OEM logo. 477 478 blkdevparts= Manual partition parsing of block device(s) for 479 embedded devices based on command line input. 480 See Documentation/block/cmdline-partition.rst 481 482 boot_delay= Milliseconds to delay each printk during boot. 483 Values larger than 10 seconds (10000) are changed to 484 no delay (0). 485 Format: integer 486 487 bootconfig [KNL] 488 Extended command line options can be added to an initrd 489 and this will cause the kernel to look for it. 490 491 See Documentation/admin-guide/bootconfig.rst 492 493 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 494 bttv.radio= Most important insmod options are available as 495 kernel args too. 496 bttv.pll= See Documentation/admin-guide/media/bttv.rst 497 bttv.tuner= 498 499 bulk_remove=off [PPC] This parameter disables the use of the pSeries 500 firmware feature for flushing multiple hpte entries 501 at a time. 502 503 c101= [NET] Moxa C101 synchronous serial card 504 505 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 506 Sometimes CPU hardware bugs make them report the cache 507 size incorrectly. The kernel will attempt work arounds 508 to fix known problems, but for some CPUs it is not 509 possible to determine what the correct size should be. 510 This option provides an override for these situations. 511 512 carrier_timeout= 513 [NET] Specifies amount of time (in seconds) that 514 the kernel should wait for a network carrier. By default 515 it waits 120 seconds. 516 517 ca_keys= [KEYS] This parameter identifies a specific key(s) on 518 the system trusted keyring to be used for certificate 519 trust validation. 520 format: { id:<keyid> | builtin } 521 522 cca= [MIPS] Override the kernel pages' cache coherency 523 algorithm. Accepted values range from 0 to 7 524 inclusive. See arch/mips/include/asm/pgtable-bits.h 525 for platform specific values (SB1, Loongson3 and 526 others). 527 528 ccw_timeout_log [S390] 529 See Documentation/s390/common_io.rst for details. 530 531 cgroup_disable= [KNL] Disable a particular controller or optional feature 532 Format: {name of the controller(s) or feature(s) to disable} 533 The effects of cgroup_disable=foo are: 534 - foo isn't auto-mounted if you mount all cgroups in 535 a single hierarchy 536 - foo isn't visible as an individually mountable 537 subsystem 538 - if foo is an optional feature then the feature is 539 disabled and corresponding cgroup files are not 540 created 541 {Currently only "memory" controller deal with this and 542 cut the overhead, others just disable the usage. So 543 only cgroup_disable=memory is actually worthy} 544 Specifying "pressure" disables per-cgroup pressure 545 stall information accounting feature 546 547 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 548 Format: { { controller | "all" | "named" } 549 [,{ controller | "all" | "named" }...] } 550 Like cgroup_disable, but only applies to cgroup v1; 551 the blacklisted controllers remain available in cgroup2. 552 "all" blacklists all controllers and "named" disables 553 named mounts. Specifying both "all" and "named" disables 554 all v1 hierarchies. 555 556 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 557 Format: <string> 558 nosocket -- Disable socket memory accounting. 559 nokmem -- Disable kernel memory accounting. 560 561 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 562 Format: { "0" | "1" } 563 See security/selinux/Kconfig help text. 564 0 -- check protection applied by kernel (includes 565 any implied execute protection). 566 1 -- check protection requested by application. 567 Default value is set via a kernel config option. 568 Value can be changed at runtime via 569 /sys/fs/selinux/checkreqprot. 570 Setting checkreqprot to 1 is deprecated. 571 572 cio_ignore= [S390] 573 See Documentation/s390/common_io.rst for details. 574 575 clearcpuid=X[,X...] [X86] 576 Disable CPUID feature X for the kernel. See 577 arch/x86/include/asm/cpufeatures.h for the valid bit 578 numbers X. Note the Linux-specific bits are not necessarily 579 stable over kernel options, but the vendor-specific 580 ones should be. 581 X can also be a string as appearing in the flags: line 582 in /proc/cpuinfo which does not have the above 583 instability issue. However, not all features have names 584 in /proc/cpuinfo. 585 Note that using this option will taint your kernel. 586 Also note that user programs calling CPUID directly 587 or using the feature without checking anything 588 will still see it. This just prevents it from 589 being used by the kernel or shown in /proc/cpuinfo. 590 Also note the kernel might malfunction if you disable 591 some critical bits. 592 593 clk_ignore_unused 594 [CLK] 595 Prevents the clock framework from automatically gating 596 clocks that have not been explicitly enabled by a Linux 597 device driver but are enabled in hardware at reset or 598 by the bootloader/firmware. Note that this does not 599 force such clocks to be always-on nor does it reserve 600 those clocks in any way. This parameter is useful for 601 debug and development, but should not be needed on a 602 platform with proper driver support. For more 603 information, see Documentation/driver-api/clk.rst. 604 605 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 606 [Deprecated] 607 Forces specified clocksource (if available) to be used 608 when calculating gettimeofday(). If specified 609 clocksource is not available, it defaults to PIT. 610 Format: { pit | tsc | cyclone | pmtmr } 611 612 clocksource= Override the default clocksource 613 Format: <string> 614 Override the default clocksource and use the clocksource 615 with the name specified. 616 Some clocksource names to choose from, depending on 617 the platform: 618 [all] jiffies (this is the base, fallback clocksource) 619 [ACPI] acpi_pm 620 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 621 pxa_timer,timer3,32k_counter,timer0_1 622 [X86-32] pit,hpet,tsc; 623 scx200_hrt on Geode; cyclone on IBM x440 624 [MIPS] MIPS 625 [PARISC] cr16 626 [S390] tod 627 [SH] SuperH 628 [SPARC64] tick 629 [X86-64] hpet,tsc 630 631 clocksource.arm_arch_timer.evtstrm= 632 [ARM,ARM64] 633 Format: <bool> 634 Enable/disable the eventstream feature of the ARM 635 architected timer so that code using WFE-based polling 636 loops can be debugged more effectively on production 637 systems. 638 639 clocksource.max_cswd_read_retries= [KNL] 640 Number of clocksource_watchdog() retries due to 641 external delays before the clock will be marked 642 unstable. Defaults to two retries, that is, 643 three attempts to read the clock under test. 644 645 clocksource.verify_n_cpus= [KNL] 646 Limit the number of CPUs checked for clocksources 647 marked with CLOCK_SOURCE_VERIFY_PERCPU that 648 are marked unstable due to excessive skew. 649 A negative value says to check all CPUs, while 650 zero says not to check any. Values larger than 651 nr_cpu_ids are silently truncated to nr_cpu_ids. 652 The actual CPUs are chosen randomly, with 653 no replacement if the same CPU is chosen twice. 654 655 clocksource-wdtest.holdoff= [KNL] 656 Set the time in seconds that the clocksource 657 watchdog test waits before commencing its tests. 658 Defaults to zero when built as a module and to 659 10 seconds when built into the kernel. 660 661 cma=nn[MG]@[start[MG][-end[MG]]] 662 [KNL,CMA] 663 Sets the size of kernel global memory area for 664 contiguous memory allocations and optionally the 665 placement constraint by the physical address range of 666 memory allocations. A value of 0 disables CMA 667 altogether. For more information, see 668 kernel/dma/contiguous.c 669 670 cma_pernuma=nn[MG] 671 [ARM64,KNL,CMA] 672 Sets the size of kernel per-numa memory area for 673 contiguous memory allocations. A value of 0 disables 674 per-numa CMA altogether. And If this option is not 675 specificed, the default value is 0. 676 With per-numa CMA enabled, DMA users on node nid will 677 first try to allocate buffer from the pernuma area 678 which is located in node nid, if the allocation fails, 679 they will fallback to the global default memory area. 680 681 cmo_free_hint= [PPC] Format: { yes | no } 682 Specify whether pages are marked as being inactive 683 when they are freed. This is used in CMO environments 684 to determine OS memory pressure for page stealing by 685 a hypervisor. 686 Default: yes 687 688 coherent_pool=nn[KMG] [ARM,KNL] 689 Sets the size of memory pool for coherent, atomic dma 690 allocations, by default set to 256K. 691 692 com20020= [HW,NET] ARCnet - COM20020 chipset 693 Format: 694 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 695 696 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 697 Format: <io>[,<irq>] 698 699 com90xx= [HW,NET] 700 ARCnet - COM90xx chipset (memory-mapped buffers) 701 Format: <io>[,<irq>[,<memstart>]] 702 703 condev= [HW,S390] console device 704 conmode= 705 706 console= [KNL] Output console device and options. 707 708 tty<n> Use the virtual console device <n>. 709 710 ttyS<n>[,options] 711 ttyUSB0[,options] 712 Use the specified serial port. The options are of 713 the form "bbbbpnf", where "bbbb" is the baud rate, 714 "p" is parity ("n", "o", or "e"), "n" is number of 715 bits, and "f" is flow control ("r" for RTS or 716 omit it). Default is "9600n8". 717 718 See Documentation/admin-guide/serial-console.rst for more 719 information. See 720 Documentation/networking/netconsole.rst for an 721 alternative. 722 723 uart[8250],io,<addr>[,options] 724 uart[8250],mmio,<addr>[,options] 725 uart[8250],mmio16,<addr>[,options] 726 uart[8250],mmio32,<addr>[,options] 727 uart[8250],0x<addr>[,options] 728 Start an early, polled-mode console on the 8250/16550 729 UART at the specified I/O port or MMIO address, 730 switching to the matching ttyS device later. 731 MMIO inter-register address stride is either 8-bit 732 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 733 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 734 to be equivalent to 'mmio'. 'options' are specified in 735 the same format described for ttyS above; if unspecified, 736 the h/w is not re-initialized. 737 738 hvc<n> Use the hypervisor console device <n>. This is for 739 both Xen and PowerPC hypervisors. 740 741 { null | "" } 742 Use to disable console output, i.e., to have kernel 743 console messages discarded. 744 This must be the only console= parameter used on the 745 kernel command line. 746 747 If the device connected to the port is not a TTY but a braille 748 device, prepend "brl," before the device type, for instance 749 console=brl,ttyS0 750 For now, only VisioBraille is supported. 751 752 console_msg_format= 753 [KNL] Change console messages format 754 default 755 By default we print messages on consoles in 756 "[time stamp] text\n" format (time stamp may not be 757 printed, depending on CONFIG_PRINTK_TIME or 758 `printk_time' param). 759 syslog 760 Switch to syslog format: "<%u>[time stamp] text\n" 761 IOW, each message will have a facility and loglevel 762 prefix. The format is similar to one used by syslog() 763 syscall, or to executing "dmesg -S --raw" or to reading 764 from /proc/kmsg. 765 766 consoleblank= [KNL] The console blank (screen saver) timeout in 767 seconds. A value of 0 disables the blank timer. 768 Defaults to 0. 769 770 coredump_filter= 771 [KNL] Change the default value for 772 /proc/<pid>/coredump_filter. 773 See also Documentation/filesystems/proc.rst. 774 775 coresight_cpu_debug.enable 776 [ARM,ARM64] 777 Format: <bool> 778 Enable/disable the CPU sampling based debugging. 779 0: default value, disable debugging 780 1: enable debugging at boot time 781 782 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 783 Format: 784 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 785 786 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 787 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 788 Some features depend on CPU0. Known dependencies are: 789 1. Resume from suspend/hibernate depends on CPU0. 790 Suspend/hibernate will fail if CPU0 is offline and you 791 need to online CPU0 before suspend/hibernate. 792 2. PIC interrupts also depend on CPU0. CPU0 can't be 793 removed if a PIC interrupt is detected. 794 It's said poweroff/reboot may depend on CPU0 on some 795 machines although I haven't seen such issues so far 796 after CPU0 is offline on a few tested machines. 797 If the dependencies are under your control, you can 798 turn on cpu0_hotplug. 799 800 cpuidle.off=1 [CPU_IDLE] 801 disable the cpuidle sub-system 802 803 cpuidle.governor= 804 [CPU_IDLE] Name of the cpuidle governor to use. 805 806 cpufreq.off=1 [CPU_FREQ] 807 disable the cpufreq sub-system 808 809 cpufreq.default_governor= 810 [CPU_FREQ] Name of the default cpufreq governor or 811 policy to use. This governor must be registered in the 812 kernel before the cpufreq driver probes. 813 814 cpu_init_udelay=N 815 [X86] Delay for N microsec between assert and de-assert 816 of APIC INIT to start processors. This delay occurs 817 on every CPU online, such as boot, and resume from suspend. 818 Default: 10000 819 820 crash_kexec_post_notifiers 821 Run kdump after running panic-notifiers and dumping 822 kmsg. This only for the users who doubt kdump always 823 succeeds in any situation. 824 Note that this also increases risks of kdump failure, 825 because some panic notifiers can make the crashed 826 kernel more unstable. 827 828 crashkernel=size[KMG][@offset[KMG]] 829 [KNL] Using kexec, Linux can switch to a 'crash kernel' 830 upon panic. This parameter reserves the physical 831 memory region [offset, offset + size] for that kernel 832 image. If '@offset' is omitted, then a suitable offset 833 is selected automatically. 834 [KNL, X86-64] Select a region under 4G first, and 835 fall back to reserve region above 4G when '@offset' 836 hasn't been specified. 837 See Documentation/admin-guide/kdump/kdump.rst for further details. 838 839 crashkernel=range1:size1[,range2:size2,...][@offset] 840 [KNL] Same as above, but depends on the memory 841 in the running system. The syntax of range is 842 start-[end] where start and end are both 843 a memory unit (amount[KMG]). See also 844 Documentation/admin-guide/kdump/kdump.rst for an example. 845 846 crashkernel=size[KMG],high 847 [KNL, X86-64, ARM64] range could be above 4G. Allow kernel 848 to allocate physical memory region from top, so could 849 be above 4G if system have more than 4G ram installed. 850 Otherwise memory region will be allocated below 4G, if 851 available. 852 It will be ignored if crashkernel=X is specified. 853 crashkernel=size[KMG],low 854 [KNL, X86-64] range under 4G. When crashkernel=X,high 855 is passed, kernel could allocate physical memory region 856 above 4G, that cause second kernel crash on system 857 that require some amount of low memory, e.g. swiotlb 858 requires at least 64M+32K low memory, also enough extra 859 low memory is needed to make sure DMA buffers for 32-bit 860 devices won't run out. Kernel would try to allocate 861 at least 256M below 4G automatically. 862 This one lets the user specify own low range under 4G 863 for second kernel instead. 864 0: to disable low allocation. 865 It will be ignored when crashkernel=X,high is not used 866 or memory reserved is below 4G. 867 868 [KNL, ARM64] range in low memory. 869 This one lets the user specify a low range in the 870 DMA zone for the crash dump kernel. 871 It will be ignored when crashkernel=X,high is not used 872 or memory reserved is located in the DMA zones. 873 874 cryptomgr.notests 875 [KNL] Disable crypto self-tests 876 877 cs89x0_dma= [HW,NET] 878 Format: <dma> 879 880 cs89x0_media= [HW,NET] 881 Format: { rj45 | aui | bnc } 882 883 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call 884 handling. When switched on, additional debug data is 885 printed to the console in case a hanging CPU is 886 detected, and that CPU is pinged again in order to try 887 to resolve the hang situation. 888 0: disable csdlock debugging (default) 889 1: enable basic csdlock debugging (minor impact) 890 ext: enable extended csdlock debugging (more impact, 891 but more data) 892 893 dasd= [HW,NET] 894 See header of drivers/s390/block/dasd_devmap.c. 895 896 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 897 (one device per port) 898 Format: <port#>,<type> 899 See also Documentation/input/devices/joystick-parport.rst 900 901 debug [KNL] Enable kernel debugging (events log level). 902 903 debug_boot_weak_hash 904 [KNL] Enable printing [hashed] pointers early in the 905 boot sequence. If enabled, we use a weak hash instead 906 of siphash to hash pointers. Use this option if you are 907 seeing instances of '(___ptrval___)') and need to see a 908 value (hashed pointer) instead. Cryptographically 909 insecure, please do not use on production kernels. 910 911 debug_locks_verbose= 912 [KNL] verbose locking self-tests 913 Format: <int> 914 Print debugging info while doing the locking API 915 self-tests. 916 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 917 (no extra messages), setting it to -1 (all bits set) 918 will print _a_lot_ more information - normally only 919 useful to lockdep developers. 920 921 debug_objects [KNL] Enable object debugging 922 923 no_debug_objects 924 [KNL] Disable object debugging 925 926 debug_guardpage_minorder= 927 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 928 parameter allows control of the order of pages that will 929 be intentionally kept free (and hence protected) by the 930 buddy allocator. Bigger value increase the probability 931 of catching random memory corruption, but reduce the 932 amount of memory for normal system use. The maximum 933 possible value is MAX_ORDER/2. Setting this parameter 934 to 1 or 2 should be enough to identify most random 935 memory corruption problems caused by bugs in kernel or 936 driver code when a CPU writes to (or reads from) a 937 random memory location. Note that there exists a class 938 of memory corruptions problems caused by buggy H/W or 939 F/W or by drivers badly programing DMA (basically when 940 memory is written at bus level and the CPU MMU is 941 bypassed) which are not detectable by 942 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 943 tracking down these problems. 944 945 debug_pagealloc= 946 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 947 enables the feature at boot time. By default, it is 948 disabled and the system will work mostly the same as a 949 kernel built without CONFIG_DEBUG_PAGEALLOC. 950 Note: to get most of debug_pagealloc error reports, it's 951 useful to also enable the page_owner functionality. 952 on: enable the feature 953 954 debugfs= [KNL] This parameter enables what is exposed to userspace 955 and debugfs internal clients. 956 Format: { on, no-mount, off } 957 on: All functions are enabled. 958 no-mount: 959 Filesystem is not registered but kernel clients can 960 access APIs and a crashkernel can be used to read 961 its content. There is nothing to mount. 962 off: Filesystem is not registered and clients 963 get a -EPERM as result when trying to register files 964 or directories within debugfs. 965 This is equivalent of the runtime functionality if 966 debugfs was not enabled in the kernel at all. 967 Default value is set in build-time with a kernel configuration. 968 969 debugpat [X86] Enable PAT debugging 970 971 default_hugepagesz= 972 [HW] The size of the default HugeTLB page. This is 973 the size represented by the legacy /proc/ hugepages 974 APIs. In addition, this is the default hugetlb size 975 used for shmget(), mmap() and mounting hugetlbfs 976 filesystems. If not specified, defaults to the 977 architecture's default huge page size. Huge page 978 sizes are architecture dependent. See also 979 Documentation/admin-guide/mm/hugetlbpage.rst. 980 Format: size[KMG] 981 982 deferred_probe_timeout= 983 [KNL] Debugging option to set a timeout in seconds for 984 deferred probe to give up waiting on dependencies to 985 probe. Only specific dependencies (subsystems or 986 drivers) that have opted in will be ignored. A timeout 987 of 0 will timeout at the end of initcalls. If the time 988 out hasn't expired, it'll be restarted by each 989 successful driver registration. This option will also 990 dump out devices still on the deferred probe list after 991 retrying. 992 993 delayacct [KNL] Enable per-task delay accounting 994 995 dell_smm_hwmon.ignore_dmi= 996 [HW] Continue probing hardware even if DMI data 997 indicates that the driver is running on unsupported 998 hardware. 999 1000 dell_smm_hwmon.force= 1001 [HW] Activate driver even if SMM BIOS signature does 1002 not match list of supported models and enable otherwise 1003 blacklisted features. 1004 1005 dell_smm_hwmon.power_status= 1006 [HW] Report power status in /proc/i8k 1007 (disabled by default). 1008 1009 dell_smm_hwmon.restricted= 1010 [HW] Allow controlling fans only if SYS_ADMIN 1011 capability is set. 1012 1013 dell_smm_hwmon.fan_mult= 1014 [HW] Factor to multiply fan speed with. 1015 1016 dell_smm_hwmon.fan_max= 1017 [HW] Maximum configurable fan speed. 1018 1019 dfltcc= [HW,S390] 1020 Format: { on | off | def_only | inf_only | always } 1021 on: s390 zlib hardware support for compression on 1022 level 1 and decompression (default) 1023 off: No s390 zlib hardware support 1024 def_only: s390 zlib hardware support for deflate 1025 only (compression on level 1) 1026 inf_only: s390 zlib hardware support for inflate 1027 only (decompression) 1028 always: Same as 'on' but ignores the selected compression 1029 level always using hardware support (used for debugging) 1030 1031 dhash_entries= [KNL] 1032 Set number of hash buckets for dentry cache. 1033 1034 disable_1tb_segments [PPC] 1035 Disables the use of 1TB hash page table segments. This 1036 causes the kernel to fall back to 256MB segments which 1037 can be useful when debugging issues that require an SLB 1038 miss to occur. 1039 1040 stress_slb [PPC] 1041 Limits the number of kernel SLB entries, and flushes 1042 them frequently to increase the rate of SLB faults 1043 on kernel addresses. 1044 1045 disable= [IPV6] 1046 See Documentation/networking/ipv6.rst. 1047 1048 disable_radix [PPC] 1049 Disable RADIX MMU mode on POWER9 1050 1051 radix_hcall_invalidate=on [PPC/PSERIES] 1052 Disable RADIX GTSE feature and use hcall for TLB 1053 invalidate. 1054 1055 disable_tlbie [PPC] 1056 Disable TLBIE instruction. Currently does not work 1057 with KVM, with HASH MMU, or with coherent accelerators. 1058 1059 disable_cpu_apicid= [X86,APIC,SMP] 1060 Format: <int> 1061 The number of initial APIC ID for the 1062 corresponding CPU to be disabled at boot, 1063 mostly used for the kdump 2nd kernel to 1064 disable BSP to wake up multiple CPUs without 1065 causing system reset or hang due to sending 1066 INIT from AP to BSP. 1067 1068 disable_ddw [PPC/PSERIES] 1069 Disable Dynamic DMA Window support. Use this 1070 to workaround buggy firmware. 1071 1072 disable_ipv6= [IPV6] 1073 See Documentation/networking/ipv6.rst. 1074 1075 disable_mtrr_cleanup [X86] 1076 The kernel tries to adjust MTRR layout from continuous 1077 to discrete, to make X server driver able to add WB 1078 entry later. This parameter disables that. 1079 1080 disable_mtrr_trim [X86, Intel and AMD only] 1081 By default the kernel will trim any uncacheable 1082 memory out of your available memory pool based on 1083 MTRR settings. This parameter disables that behavior, 1084 possibly causing your machine to run very slowly. 1085 1086 disable_timer_pin_1 [X86] 1087 Disable PIN 1 of APIC timer 1088 Can be useful to work around chipset bugs. 1089 1090 dis_ucode_ldr [X86] Disable the microcode loader. 1091 1092 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1093 this option disables the debugging code at boot. 1094 1095 dma_debug_entries=<number> 1096 This option allows to tune the number of preallocated 1097 entries for DMA-API debugging code. One entry is 1098 required per DMA-API allocation. Use this if the 1099 DMA-API debugging code disables itself because the 1100 architectural default is too low. 1101 1102 dma_debug_driver=<driver_name> 1103 With this option the DMA-API debugging driver 1104 filter feature can be enabled at boot time. Just 1105 pass the driver to filter for as the parameter. 1106 The filter can be disabled or changed to another 1107 driver later using sysfs. 1108 1109 driver_async_probe= [KNL] 1110 List of driver names to be probed asynchronously. * 1111 matches with all driver names. If * is specified, the 1112 rest of the listed driver names are those that will NOT 1113 match the *. 1114 Format: <driver_name1>,<driver_name2>... 1115 1116 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1117 Broken monitors, graphic adapters, KVMs and EDIDless 1118 panels may send no or incorrect EDID data sets. 1119 This parameter allows to specify an EDID data sets 1120 in the /lib/firmware directory that are used instead. 1121 Generic built-in EDID data sets are used, if one of 1122 edid/1024x768.bin, edid/1280x1024.bin, 1123 edid/1680x1050.bin, or edid/1920x1080.bin is given 1124 and no file with the same name exists. Details and 1125 instructions how to build your own EDID data are 1126 available in Documentation/admin-guide/edid.rst. An EDID 1127 data set will only be used for a particular connector, 1128 if its name and a colon are prepended to the EDID 1129 name. Each connector may use a unique EDID data 1130 set by separating the files with a comma. An EDID 1131 data set with no connector name will be used for 1132 any connectors not explicitly specified. 1133 1134 dscc4.setup= [NET] 1135 1136 dt_cpu_ftrs= [PPC] 1137 Format: {"off" | "known"} 1138 Control how the dt_cpu_ftrs device-tree binding is 1139 used for CPU feature discovery and setup (if it 1140 exists). 1141 off: Do not use it, fall back to legacy cpu table. 1142 known: Do not pass through unknown features to guests 1143 or userspace, only those that the kernel is aware of. 1144 1145 dump_apple_properties [X86] 1146 Dump name and content of EFI device properties on 1147 x86 Macs. Useful for driver authors to determine 1148 what data is available or for reverse-engineering. 1149 1150 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1151 <module>.dyndbg[="val"] 1152 Enable debug messages at boot time. See 1153 Documentation/admin-guide/dynamic-debug-howto.rst 1154 for details. 1155 1156 nopku [X86] Disable Memory Protection Keys CPU feature found 1157 in some Intel CPUs. 1158 1159 <module>.async_probe[=<bool>] [KNL] 1160 If no <bool> value is specified or if the value 1161 specified is not a valid <bool>, enable asynchronous 1162 probe on this module. Otherwise, enable/disable 1163 asynchronous probe on this module as indicated by the 1164 <bool> value. See also: module.async_probe 1165 1166 early_ioremap_debug [KNL] 1167 Enable debug messages in early_ioremap support. This 1168 is useful for tracking down temporary early mappings 1169 which are not unmapped. 1170 1171 earlycon= [KNL] Output early console device and options. 1172 1173 When used with no options, the early console is 1174 determined by stdout-path property in device tree's 1175 chosen node or the ACPI SPCR table if supported by 1176 the platform. 1177 1178 cdns,<addr>[,options] 1179 Start an early, polled-mode console on a Cadence 1180 (xuartps) serial port at the specified address. Only 1181 supported option is baud rate. If baud rate is not 1182 specified, the serial port must already be setup and 1183 configured. 1184 1185 uart[8250],io,<addr>[,options] 1186 uart[8250],mmio,<addr>[,options] 1187 uart[8250],mmio32,<addr>[,options] 1188 uart[8250],mmio32be,<addr>[,options] 1189 uart[8250],0x<addr>[,options] 1190 Start an early, polled-mode console on the 8250/16550 1191 UART at the specified I/O port or MMIO address. 1192 MMIO inter-register address stride is either 8-bit 1193 (mmio) or 32-bit (mmio32 or mmio32be). 1194 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1195 to be equivalent to 'mmio'. 'options' are specified 1196 in the same format described for "console=ttyS<n>"; if 1197 unspecified, the h/w is not initialized. 1198 1199 pl011,<addr> 1200 pl011,mmio32,<addr> 1201 Start an early, polled-mode console on a pl011 serial 1202 port at the specified address. The pl011 serial port 1203 must already be setup and configured. Options are not 1204 yet supported. If 'mmio32' is specified, then only 1205 the driver will use only 32-bit accessors to read/write 1206 the device registers. 1207 1208 liteuart,<addr> 1209 Start an early console on a litex serial port at the 1210 specified address. The serial port must already be 1211 setup and configured. Options are not yet supported. 1212 1213 meson,<addr> 1214 Start an early, polled-mode console on a meson serial 1215 port at the specified address. The serial port must 1216 already be setup and configured. Options are not yet 1217 supported. 1218 1219 msm_serial,<addr> 1220 Start an early, polled-mode console on an msm serial 1221 port at the specified address. The serial port 1222 must already be setup and configured. Options are not 1223 yet supported. 1224 1225 msm_serial_dm,<addr> 1226 Start an early, polled-mode console on an msm serial 1227 dm port at the specified address. The serial port 1228 must already be setup and configured. Options are not 1229 yet supported. 1230 1231 owl,<addr> 1232 Start an early, polled-mode console on a serial port 1233 of an Actions Semi SoC, such as S500 or S900, at the 1234 specified address. The serial port must already be 1235 setup and configured. Options are not yet supported. 1236 1237 rda,<addr> 1238 Start an early, polled-mode console on a serial port 1239 of an RDA Micro SoC, such as RDA8810PL, at the 1240 specified address. The serial port must already be 1241 setup and configured. Options are not yet supported. 1242 1243 sbi 1244 Use RISC-V SBI (Supervisor Binary Interface) for early 1245 console. 1246 1247 smh Use ARM semihosting calls for early console. 1248 1249 s3c2410,<addr> 1250 s3c2412,<addr> 1251 s3c2440,<addr> 1252 s3c6400,<addr> 1253 s5pv210,<addr> 1254 exynos4210,<addr> 1255 Use early console provided by serial driver available 1256 on Samsung SoCs, requires selecting proper type and 1257 a correct base address of the selected UART port. The 1258 serial port must already be setup and configured. 1259 Options are not yet supported. 1260 1261 lantiq,<addr> 1262 Start an early, polled-mode console on a lantiq serial 1263 (lqasc) port at the specified address. The serial port 1264 must already be setup and configured. Options are not 1265 yet supported. 1266 1267 lpuart,<addr> 1268 lpuart32,<addr> 1269 Use early console provided by Freescale LP UART driver 1270 found on Freescale Vybrid and QorIQ LS1021A processors. 1271 A valid base address must be provided, and the serial 1272 port must already be setup and configured. 1273 1274 ec_imx21,<addr> 1275 ec_imx6q,<addr> 1276 Start an early, polled-mode, output-only console on the 1277 Freescale i.MX UART at the specified address. The UART 1278 must already be setup and configured. 1279 1280 ar3700_uart,<addr> 1281 Start an early, polled-mode console on the 1282 Armada 3700 serial port at the specified 1283 address. The serial port must already be setup 1284 and configured. Options are not yet supported. 1285 1286 qcom_geni,<addr> 1287 Start an early, polled-mode console on a Qualcomm 1288 Generic Interface (GENI) based serial port at the 1289 specified address. The serial port must already be 1290 setup and configured. Options are not yet supported. 1291 1292 efifb,[options] 1293 Start an early, unaccelerated console on the EFI 1294 memory mapped framebuffer (if available). On cache 1295 coherent non-x86 systems that use system memory for 1296 the framebuffer, pass the 'ram' option so that it is 1297 mapped with the correct attributes. 1298 1299 linflex,<addr> 1300 Use early console provided by Freescale LINFlexD UART 1301 serial driver for NXP S32V234 SoCs. A valid base 1302 address must be provided, and the serial port must 1303 already be setup and configured. 1304 1305 earlyprintk= [X86,SH,ARM,M68k,S390] 1306 earlyprintk=vga 1307 earlyprintk=sclp 1308 earlyprintk=xen 1309 earlyprintk=serial[,ttySn[,baudrate]] 1310 earlyprintk=serial[,0x...[,baudrate]] 1311 earlyprintk=ttySn[,baudrate] 1312 earlyprintk=dbgp[debugController#] 1313 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1314 earlyprintk=xdbc[xhciController#] 1315 1316 earlyprintk is useful when the kernel crashes before 1317 the normal console is initialized. It is not enabled by 1318 default because it has some cosmetic problems. 1319 1320 Append ",keep" to not disable it when the real console 1321 takes over. 1322 1323 Only one of vga, serial, or usb debug port can 1324 be used at a time. 1325 1326 Currently only ttyS0 and ttyS1 may be specified by 1327 name. Other I/O ports may be explicitly specified 1328 on some architectures (x86 and arm at least) by 1329 replacing ttySn with an I/O port address, like this: 1330 earlyprintk=serial,0x1008,115200 1331 You can find the port for a given device in 1332 /proc/tty/driver/serial: 1333 2: uart:ST16650V2 port:00001008 irq:18 ... 1334 1335 Interaction with the standard serial driver is not 1336 very good. 1337 1338 The VGA output is eventually overwritten by 1339 the real console. 1340 1341 The xen option can only be used in Xen domains. 1342 1343 The sclp output can only be used on s390. 1344 1345 The optional "force" to "pciserial" enables use of a 1346 PCI device even when its classcode is not of the 1347 UART class. 1348 1349 edac_report= [HW,EDAC] Control how to report EDAC event 1350 Format: {"on" | "off" | "force"} 1351 on: enable EDAC to report H/W event. May be overridden 1352 by other higher priority error reporting module. 1353 off: disable H/W event reporting through EDAC. 1354 force: enforce the use of EDAC to report H/W event. 1355 default: on. 1356 1357 edd= [EDD] 1358 Format: {"off" | "on" | "skip[mbr]"} 1359 1360 efi= [EFI] 1361 Format: { "debug", "disable_early_pci_dma", 1362 "nochunk", "noruntime", "nosoftreserve", 1363 "novamap", "no_disable_early_pci_dma" } 1364 debug: enable misc debug output. 1365 disable_early_pci_dma: disable the busmaster bit on all 1366 PCI bridges while in the EFI boot stub. 1367 nochunk: disable reading files in "chunks" in the EFI 1368 boot stub, as chunking can cause problems with some 1369 firmware implementations. 1370 noruntime : disable EFI runtime services support 1371 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1372 attribute may cause the kernel to reserve the 1373 memory range for a memory mapping driver to 1374 claim. Specify efi=nosoftreserve to disable this 1375 reservation and treat the memory by its base type 1376 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1377 novamap: do not call SetVirtualAddressMap(). 1378 no_disable_early_pci_dma: Leave the busmaster bit set 1379 on all PCI bridges while in the EFI boot stub 1380 1381 efi_no_storage_paranoia [EFI; X86] 1382 Using this parameter you can use more than 50% of 1383 your efi variable storage. Use this parameter only if 1384 you are really sure that your UEFI does sane gc and 1385 fulfills the spec otherwise your board may brick. 1386 1387 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1388 Add arbitrary attribute to specific memory range by 1389 updating original EFI memory map. 1390 Region of memory which aa attribute is added to is 1391 from ss to ss+nn. 1392 1393 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1394 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1395 attribute is added to range 0x100000000-0x180000000 and 1396 0x10a0000000-0x1120000000. 1397 1398 If efi_fake_mem=8G@9G:0x40000 is specified, the 1399 EFI_MEMORY_SP(0x40000) attribute is added to 1400 range 0x240000000-0x43fffffff. 1401 1402 Using this parameter you can do debugging of EFI memmap 1403 related features. For example, you can do debugging of 1404 Address Range Mirroring feature even if your box 1405 doesn't support it, or mark specific memory as 1406 "soft reserved". 1407 1408 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1409 that is to be dynamically loaded by Linux. If there are 1410 multiple variables with the same name but with different 1411 vendor GUIDs, all of them will be loaded. See 1412 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1413 1414 1415 eisa_irq_edge= [PARISC,HW] 1416 See header of drivers/parisc/eisa.c. 1417 1418 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1419 Format: ekgdboc=kbd 1420 1421 This is designed to be used in conjunction with 1422 the boot argument: earlyprintk=vga 1423 1424 This parameter works in place of the kgdboc parameter 1425 but can only be used if the backing tty is available 1426 very early in the boot process. For early debugging 1427 via a serial port see kgdboc_earlycon instead. 1428 1429 elanfreq= [X86-32] 1430 See comment before function elanfreq_setup() in 1431 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1432 1433 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1434 Specifies physical address of start of kernel core 1435 image elf header and optionally the size. Generally 1436 kexec loader will pass this option to capture kernel. 1437 See Documentation/admin-guide/kdump/kdump.rst for details. 1438 1439 enable_mtrr_cleanup [X86] 1440 The kernel tries to adjust MTRR layout from continuous 1441 to discrete, to make X server driver able to add WB 1442 entry later. This parameter enables that. 1443 1444 enable_timer_pin_1 [X86] 1445 Enable PIN 1 of APIC timer 1446 Can be useful to work around chipset bugs 1447 (in particular on some ATI chipsets). 1448 The kernel tries to set a reasonable default. 1449 1450 enforcing= [SELINUX] Set initial enforcing status. 1451 Format: {"0" | "1"} 1452 See security/selinux/Kconfig help text. 1453 0 -- permissive (log only, no denials). 1454 1 -- enforcing (deny and log). 1455 Default value is 0. 1456 Value can be changed at runtime via 1457 /sys/fs/selinux/enforce. 1458 1459 erst_disable [ACPI] 1460 Disable Error Record Serialization Table (ERST) 1461 support. 1462 1463 ether= [HW,NET] Ethernet cards parameters 1464 This option is obsoleted by the "netdev=" option, which 1465 has equivalent usage. See its documentation for details. 1466 1467 evm= [EVM] 1468 Format: { "fix" } 1469 Permit 'security.evm' to be updated regardless of 1470 current integrity status. 1471 1472 early_page_ext [KNL] Enforces page_ext initialization to earlier 1473 stages so cover more early boot allocations. 1474 Please note that as side effect some optimizations 1475 might be disabled to achieve that (e.g. parallelized 1476 memory initialization is disabled) so the boot process 1477 might take longer, especially on systems with a lot of 1478 memory. Available with CONFIG_PAGE_EXTENSION=y. 1479 1480 failslab= 1481 fail_usercopy= 1482 fail_page_alloc= 1483 fail_make_request=[KNL] 1484 General fault injection mechanism. 1485 Format: <interval>,<probability>,<space>,<times> 1486 See also Documentation/fault-injection/. 1487 1488 fb_tunnels= [NET] 1489 Format: { initns | none } 1490 See Documentation/admin-guide/sysctl/net.rst for 1491 fb_tunnels_only_for_init_ns 1492 1493 floppy= [HW] 1494 See Documentation/admin-guide/blockdev/floppy.rst. 1495 1496 force_pal_cache_flush 1497 [IA-64] Avoid check_sal_cache_flush which may hang on 1498 buggy SAL_CACHE_FLUSH implementations. Using this 1499 parameter will force ia64_sal_cache_flush to call 1500 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1501 1502 forcepae [X86-32] 1503 Forcefully enable Physical Address Extension (PAE). 1504 Many Pentium M systems disable PAE but may have a 1505 functionally usable PAE implementation. 1506 Warning: use of this parameter will taint the kernel 1507 and may cause unknown problems. 1508 1509 ftrace=[tracer] 1510 [FTRACE] will set and start the specified tracer 1511 as early as possible in order to facilitate early 1512 boot debugging. 1513 1514 ftrace_boot_snapshot 1515 [FTRACE] On boot up, a snapshot will be taken of the 1516 ftrace ring buffer that can be read at: 1517 /sys/kernel/tracing/snapshot. 1518 This is useful if you need tracing information from kernel 1519 boot up that is likely to be overridden by user space 1520 start up functionality. 1521 1522 ftrace_dump_on_oops[=orig_cpu] 1523 [FTRACE] will dump the trace buffers on oops. 1524 If no parameter is passed, ftrace will dump 1525 buffers of all CPUs, but if you pass orig_cpu, it will 1526 dump only the buffer of the CPU that triggered the 1527 oops. 1528 1529 ftrace_filter=[function-list] 1530 [FTRACE] Limit the functions traced by the function 1531 tracer at boot up. function-list is a comma-separated 1532 list of functions. This list can be changed at run 1533 time by the set_ftrace_filter file in the debugfs 1534 tracing directory. 1535 1536 ftrace_notrace=[function-list] 1537 [FTRACE] Do not trace the functions specified in 1538 function-list. This list can be changed at run time 1539 by the set_ftrace_notrace file in the debugfs 1540 tracing directory. 1541 1542 ftrace_graph_filter=[function-list] 1543 [FTRACE] Limit the top level callers functions traced 1544 by the function graph tracer at boot up. 1545 function-list is a comma-separated list of functions 1546 that can be changed at run time by the 1547 set_graph_function file in the debugfs tracing directory. 1548 1549 ftrace_graph_notrace=[function-list] 1550 [FTRACE] Do not trace from the functions specified in 1551 function-list. This list is a comma-separated list of 1552 functions that can be changed at run time by the 1553 set_graph_notrace file in the debugfs tracing directory. 1554 1555 ftrace_graph_max_depth=<uint> 1556 [FTRACE] Used with the function graph tracer. This is 1557 the max depth it will trace into a function. This value 1558 can be changed at run time by the max_graph_depth file 1559 in the tracefs tracing directory. default: 0 (no limit) 1560 1561 fw_devlink= [KNL] Create device links between consumer and supplier 1562 devices by scanning the firmware to infer the 1563 consumer/supplier relationships. This feature is 1564 especially useful when drivers are loaded as modules as 1565 it ensures proper ordering of tasks like device probing 1566 (suppliers first, then consumers), supplier boot state 1567 clean up (only after all consumers have probed), 1568 suspend/resume & runtime PM (consumers first, then 1569 suppliers). 1570 Format: { off | permissive | on | rpm } 1571 off -- Don't create device links from firmware info. 1572 permissive -- Create device links from firmware info 1573 but use it only for ordering boot state clean 1574 up (sync_state() calls). 1575 on -- Create device links from firmware info and use it 1576 to enforce probe and suspend/resume ordering. 1577 rpm -- Like "on", but also use to order runtime PM. 1578 1579 fw_devlink.strict=<bool> 1580 [KNL] Treat all inferred dependencies as mandatory 1581 dependencies. This only applies for fw_devlink=on|rpm. 1582 Format: <bool> 1583 1584 gamecon.map[2|3]= 1585 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1586 support via parallel port (up to 5 devices per port) 1587 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1588 See also Documentation/input/devices/joystick-parport.rst 1589 1590 gamma= [HW,DRM] 1591 1592 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1593 Format: off | on 1594 default: on 1595 1596 gcov_persist= [GCOV] When non-zero (default), profiling data for 1597 kernel modules is saved and remains accessible via 1598 debugfs, even when the module is unloaded/reloaded. 1599 When zero, profiling data is discarded and associated 1600 debugfs files are removed at module unload time. 1601 1602 goldfish [X86] Enable the goldfish android emulator platform. 1603 Don't use this when you are not running on the 1604 android emulator 1605 1606 gpio-mockup.gpio_mockup_ranges 1607 [HW] Sets the ranges of gpiochip of for this device. 1608 Format: <start1>,<end1>,<start2>,<end2>... 1609 gpio-mockup.gpio_mockup_named_lines 1610 [HW] Let the driver know GPIO lines should be named. 1611 1612 gpt [EFI] Forces disk with valid GPT signature but 1613 invalid Protective MBR to be treated as GPT. If the 1614 primary GPT is corrupted, it enables the backup/alternate 1615 GPT to be used instead. 1616 1617 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1618 the "Enable 0" bit of the configuration register. 1619 Format: 0 | 1 1620 Default: 0 1621 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1622 the "Enable 0" bit of the configuration register. 1623 Format: 0 | 1 1624 Default: 0 1625 grcan.select= [HW] Select which physical interface to use. 1626 Format: 0 | 1 1627 Default: 0 1628 grcan.txsize= [HW] Sets the size of the tx buffer. 1629 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1630 Default: 1024 1631 grcan.rxsize= [HW] Sets the size of the rx buffer. 1632 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1633 Default: 1024 1634 1635 hardened_usercopy= 1636 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1637 hardening is enabled for this boot. Hardened 1638 usercopy checking is used to protect the kernel 1639 from reading or writing beyond known memory 1640 allocation boundaries as a proactive defense 1641 against bounds-checking flaws in the kernel's 1642 copy_to_user()/copy_from_user() interface. 1643 on Perform hardened usercopy checks (default). 1644 off Disable hardened usercopy checks. 1645 1646 hardlockup_all_cpu_backtrace= 1647 [KNL] Should the hard-lockup detector generate 1648 backtraces on all cpus. 1649 Format: 0 | 1 1650 1651 hashdist= [KNL,NUMA] Large hashes allocated during boot 1652 are distributed across NUMA nodes. Defaults on 1653 for 64-bit NUMA, off otherwise. 1654 Format: 0 | 1 (for off | on) 1655 1656 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1657 1658 hd= [EIDE] (E)IDE hard drive subsystem geometry 1659 Format: <cyl>,<head>,<sect> 1660 1661 hest_disable [ACPI] 1662 Disable Hardware Error Source Table (HEST) support; 1663 corresponding firmware-first mode error processing 1664 logic will be disabled. 1665 1666 hibernate= [HIBERNATION] 1667 noresume Don't check if there's a hibernation image 1668 present during boot. 1669 nocompress Don't compress/decompress hibernation images. 1670 no Disable hibernation and resume. 1671 protect_image Turn on image protection during restoration 1672 (that will set all pages holding image data 1673 during restoration read-only). 1674 1675 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1676 size of <nn>. This works even on boxes that have no 1677 highmem otherwise. This also works to reduce highmem 1678 size on bigger boxes. 1679 1680 highres= [KNL] Enable/disable high resolution timer mode. 1681 Valid parameters: "on", "off" 1682 Default: "on" 1683 1684 hlt [BUGS=ARM,SH] 1685 1686 hostname= [KNL] Set the hostname (aka UTS nodename). 1687 Format: <string> 1688 This allows setting the system's hostname during early 1689 startup. This sets the name returned by gethostname. 1690 Using this parameter to set the hostname makes it 1691 possible to ensure the hostname is correctly set before 1692 any userspace processes run, avoiding the possibility 1693 that a process may call gethostname before the hostname 1694 has been explicitly set, resulting in the calling 1695 process getting an incorrect result. The string must 1696 not exceed the maximum allowed hostname length (usually 1697 64 characters) and will be truncated otherwise. 1698 1699 hpet= [X86-32,HPET] option to control HPET usage 1700 Format: { enable (default) | disable | force | 1701 verbose } 1702 disable: disable HPET and use PIT instead 1703 force: allow force enabled of undocumented chips (ICH4, 1704 VIA, nVidia) 1705 verbose: show contents of HPET registers during setup 1706 1707 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1708 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1709 1710 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1711 If this follows hugepagesz (below), it specifies 1712 the number of pages of hugepagesz to be allocated. 1713 If this is the first HugeTLB parameter on the command 1714 line, it specifies the number of pages to allocate for 1715 the default huge page size. If using node format, the 1716 number of pages to allocate per-node can be specified. 1717 See also Documentation/admin-guide/mm/hugetlbpage.rst. 1718 Format: <integer> or (node format) 1719 <node>:<integer>[,<node>:<integer>] 1720 1721 hugepagesz= 1722 [HW] The size of the HugeTLB pages. This is used in 1723 conjunction with hugepages (above) to allocate huge 1724 pages of a specific size at boot. The pair 1725 hugepagesz=X hugepages=Y can be specified once for 1726 each supported huge page size. Huge page sizes are 1727 architecture dependent. See also 1728 Documentation/admin-guide/mm/hugetlbpage.rst. 1729 Format: size[KMG] 1730 1731 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation 1732 of gigantic hugepages. Or using node format, the size 1733 of a CMA area per node can be specified. 1734 Format: nn[KMGTPE] or (node format) 1735 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 1736 1737 Reserve a CMA area of given size and allocate gigantic 1738 hugepages using the CMA allocator. If enabled, the 1739 boot-time allocation of gigantic hugepages is skipped. 1740 1741 hugetlb_free_vmemmap= 1742 [KNL] Reguires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 1743 enabled. 1744 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 1745 Allows heavy hugetlb users to free up some more 1746 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 1747 Format: { on | off (default) } 1748 1749 on: enable HVO 1750 off: disable HVO 1751 1752 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 1753 the default is on. 1754 1755 Note that the vmemmap pages may be allocated from the added 1756 memory block itself when memory_hotplug.memmap_on_memory is 1757 enabled, those vmemmap pages cannot be optimized even if this 1758 feature is enabled. Other vmemmap pages not allocated from 1759 the added memory block itself do not be affected. 1760 1761 hung_task_panic= 1762 [KNL] Should the hung task detector generate panics. 1763 Format: 0 | 1 1764 1765 A value of 1 instructs the kernel to panic when a 1766 hung task is detected. The default value is controlled 1767 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1768 option. The value selected by this boot parameter can 1769 be changed later by the kernel.hung_task_panic sysctl. 1770 1771 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1772 terminal devices. Valid values: 0..8 1773 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1774 If specified, z/VM IUCV HVC accepts connections 1775 from listed z/VM user IDs only. 1776 1777 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1778 which allow the hypervisor to 'idle' the 1779 guest on lock contention. 1780 1781 keep_bootcon [KNL] 1782 Do not unregister boot console at start. This is only 1783 useful for debugging when something happens in the window 1784 between unregistering the boot console and initializing 1785 the real console. 1786 1787 i2c_bus= [HW] Override the default board specific I2C bus speed 1788 or register an additional I2C bus that is not 1789 registered from board initialization code. 1790 Format: 1791 <bus_id>,<clkrate> 1792 1793 i8042.debug [HW] Toggle i8042 debug mode 1794 i8042.unmask_kbd_data 1795 [HW] Enable printing of interrupt data from the KBD port 1796 (disabled by default, and as a pre-condition 1797 requires that i8042.debug=1 be enabled) 1798 i8042.direct [HW] Put keyboard port into non-translated mode 1799 i8042.dumbkbd [HW] Pretend that controller can only read data from 1800 keyboard and cannot control its state 1801 (Don't attempt to blink the leds) 1802 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1803 i8042.nokbd [HW] Don't check/create keyboard port 1804 i8042.noloop [HW] Disable the AUX Loopback command while probing 1805 for the AUX port 1806 i8042.nomux [HW] Don't check presence of an active multiplexing 1807 controller 1808 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1809 controllers 1810 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1811 i8042.reset [HW] Reset the controller during init, cleanup and 1812 suspend-to-ram transitions, only during s2r 1813 transitions, or never reset 1814 Format: { 1 | Y | y | 0 | N | n } 1815 1, Y, y: always reset controller 1816 0, N, n: don't ever reset controller 1817 Default: only on s2r transitions on x86; most other 1818 architectures force reset to be always executed 1819 i8042.unlock [HW] Unlock (ignore) the keylock 1820 i8042.kbdreset [HW] Reset device connected to KBD port 1821 i8042.probe_defer 1822 [HW] Allow deferred probing upon i8042 probe errors 1823 1824 i810= [HW,DRM] 1825 1826 i915.invert_brightness= 1827 [DRM] Invert the sense of the variable that is used to 1828 set the brightness of the panel backlight. Normally a 1829 brightness value of 0 indicates backlight switched off, 1830 and the maximum of the brightness value sets the backlight 1831 to maximum brightness. If this parameter is set to 0 1832 (default) and the machine requires it, or this parameter 1833 is set to 1, a brightness value of 0 sets the backlight 1834 to maximum brightness, and the maximum of the brightness 1835 value switches the backlight off. 1836 -1 -- never invert brightness 1837 0 -- machine default 1838 1 -- force brightness inversion 1839 1840 icn= [HW,ISDN] 1841 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1842 1843 1844 idle= [X86] 1845 Format: idle=poll, idle=halt, idle=nomwait 1846 Poll forces a polling idle loop that can slightly 1847 improve the performance of waking up a idle CPU, but 1848 will use a lot of power and make the system run hot. 1849 Not recommended. 1850 idle=halt: Halt is forced to be used for CPU idle. 1851 In such case C2/C3 won't be used again. 1852 idle=nomwait: Disable mwait for CPU C-states 1853 1854 idxd.sva= [HW] 1855 Format: <bool> 1856 Allow force disabling of Shared Virtual Memory (SVA) 1857 support for the idxd driver. By default it is set to 1858 true (1). 1859 1860 idxd.tc_override= [HW] 1861 Format: <bool> 1862 Allow override of default traffic class configuration 1863 for the device. By default it is set to false (0). 1864 1865 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1866 Format: { strict | legacy | 2008 | relaxed } 1867 Default: strict 1868 1869 Choose which programs will be accepted for execution 1870 based on the IEEE 754 NaN encoding(s) supported by 1871 the FPU and the NaN encoding requested with the value 1872 of an ELF file header flag individually set by each 1873 binary. Hardware implementations are permitted to 1874 support either or both of the legacy and the 2008 NaN 1875 encoding mode. 1876 1877 Available settings are as follows: 1878 strict accept binaries that request a NaN encoding 1879 supported by the FPU 1880 legacy only accept legacy-NaN binaries, if supported 1881 by the FPU 1882 2008 only accept 2008-NaN binaries, if supported 1883 by the FPU 1884 relaxed accept any binaries regardless of whether 1885 supported by the FPU 1886 1887 The FPU emulator is always able to support both NaN 1888 encodings, so if no FPU hardware is present or it has 1889 been disabled with 'nofpu', then the settings of 1890 'legacy' and '2008' strap the emulator accordingly, 1891 'relaxed' straps the emulator for both legacy-NaN and 1892 2008-NaN, whereas 'strict' enables legacy-NaN only on 1893 legacy processors and both NaN encodings on MIPS32 or 1894 MIPS64 CPUs. 1895 1896 The setting for ABS.fmt/NEG.fmt instruction execution 1897 mode generally follows that for the NaN encoding, 1898 except where unsupported by hardware. 1899 1900 ignore_loglevel [KNL] 1901 Ignore loglevel setting - this will print /all/ 1902 kernel messages to the console. Useful for debugging. 1903 We also add it as printk module parameter, so users 1904 could change it dynamically, usually by 1905 /sys/module/printk/parameters/ignore_loglevel. 1906 1907 ignore_rlimit_data 1908 Ignore RLIMIT_DATA setting for data mappings, 1909 print warning at first misuse. Can be changed via 1910 /sys/module/kernel/parameters/ignore_rlimit_data. 1911 1912 ihash_entries= [KNL] 1913 Set number of hash buckets for inode cache. 1914 1915 ima_appraise= [IMA] appraise integrity measurements 1916 Format: { "off" | "enforce" | "fix" | "log" } 1917 default: "enforce" 1918 1919 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1920 The builtin appraise policy appraises all files 1921 owned by uid=0. 1922 1923 ima_canonical_fmt [IMA] 1924 Use the canonical format for the binary runtime 1925 measurements, instead of host native format. 1926 1927 ima_hash= [IMA] 1928 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1929 | sha512 | ... } 1930 default: "sha1" 1931 1932 The list of supported hash algorithms is defined 1933 in crypto/hash_info.h. 1934 1935 ima_policy= [IMA] 1936 The builtin policies to load during IMA setup. 1937 Format: "tcb | appraise_tcb | secure_boot | 1938 fail_securely | critical_data" 1939 1940 The "tcb" policy measures all programs exec'd, files 1941 mmap'd for exec, and all files opened with the read 1942 mode bit set by either the effective uid (euid=0) or 1943 uid=0. 1944 1945 The "appraise_tcb" policy appraises the integrity of 1946 all files owned by root. 1947 1948 The "secure_boot" policy appraises the integrity 1949 of files (eg. kexec kernel image, kernel modules, 1950 firmware, policy, etc) based on file signatures. 1951 1952 The "fail_securely" policy forces file signature 1953 verification failure also on privileged mounted 1954 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1955 flag. 1956 1957 The "critical_data" policy measures kernel integrity 1958 critical data. 1959 1960 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1961 Load a policy which meets the needs of the Trusted 1962 Computing Base. This means IMA will measure all 1963 programs exec'd, files mmap'd for exec, and all files 1964 opened for read by uid=0. 1965 1966 ima_template= [IMA] 1967 Select one of defined IMA measurements template formats. 1968 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 1969 "ima-sigv2" } 1970 Default: "ima-ng" 1971 1972 ima_template_fmt= 1973 [IMA] Define a custom template format. 1974 Format: { "field1|...|fieldN" } 1975 1976 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1977 Format: <min_file_size> 1978 Set the minimal file size for using asynchronous hash. 1979 If left unspecified, ahash usage is disabled. 1980 1981 ahash performance varies for different data sizes on 1982 different crypto accelerators. This option can be used 1983 to achieve the best performance for a particular HW. 1984 1985 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1986 Format: <bufsize> 1987 Set hashing buffer size. Default: 4k. 1988 1989 ahash performance varies for different chunk sizes on 1990 different crypto accelerators. This option can be used 1991 to achieve best performance for particular HW. 1992 1993 init= [KNL] 1994 Format: <full_path> 1995 Run specified binary instead of /sbin/init as init 1996 process. 1997 1998 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1999 for working out where the kernel is dying during 2000 startup. 2001 2002 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2003 initcall functions. Useful for debugging built-in 2004 modules and initcalls. 2005 2006 initramfs_async= [KNL] 2007 Format: <bool> 2008 Default: 1 2009 This parameter controls whether the initramfs 2010 image is unpacked asynchronously, concurrently 2011 with devices being probed and 2012 initialized. This should normally just work, 2013 but as a debugging aid, one can get the 2014 historical behaviour of the initramfs 2015 unpacking being completed before device_ and 2016 late_ initcalls. 2017 2018 initrd= [BOOT] Specify the location of the initial ramdisk 2019 2020 initrdmem= [KNL] Specify a physical address and size from which to 2021 load the initrd. If an initrd is compiled in or 2022 specified in the bootparams, it takes priority over this 2023 setting. 2024 Format: ss[KMG],nn[KMG] 2025 Default is 0, 0 2026 2027 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 2028 zeroes. 2029 Format: 0 | 1 2030 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2031 2032 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 2033 Format: 0 | 1 2034 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2035 2036 init_pkru= [X86] Specify the default memory protection keys rights 2037 register contents for all processes. 0x55555554 by 2038 default (disallow access to all but pkey 0). Can 2039 override in debugfs after boot. 2040 2041 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2042 Format: <irq> 2043 2044 int_pln_enable [X86] Enable power limit notification interrupt 2045 2046 integrity_audit=[IMA] 2047 Format: { "0" | "1" } 2048 0 -- basic integrity auditing messages. (Default) 2049 1 -- additional integrity auditing messages. 2050 2051 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2052 on 2053 Enable intel iommu driver. 2054 off 2055 Disable intel iommu driver. 2056 igfx_off [Default Off] 2057 By default, gfx is mapped as normal device. If a gfx 2058 device has a dedicated DMAR unit, the DMAR unit is 2059 bypassed by not enabling DMAR with this option. In 2060 this case, gfx device will use physical address for 2061 DMA. 2062 strict [Default Off] 2063 Deprecated, equivalent to iommu.strict=1. 2064 sp_off [Default Off] 2065 By default, super page will be supported if Intel IOMMU 2066 has the capability. With this option, super page will 2067 not be supported. 2068 sm_on 2069 Enable the Intel IOMMU scalable mode if the hardware 2070 advertises that it has support for the scalable mode 2071 translation. 2072 sm_off 2073 Disallow use of the Intel IOMMU scalable mode. 2074 tboot_noforce [Default Off] 2075 Do not force the Intel IOMMU enabled under tboot. 2076 By default, tboot will force Intel IOMMU on, which 2077 could harm performance of some high-throughput 2078 devices like 40GBit network cards, even if identity 2079 mapping is enabled. 2080 Note that using this option lowers the security 2081 provided by tboot because it makes the system 2082 vulnerable to DMA attacks. 2083 2084 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2085 0 disables intel_idle and fall back on acpi_idle. 2086 1 to 9 specify maximum depth of C-state. 2087 2088 intel_pstate= [X86] 2089 disable 2090 Do not enable intel_pstate as the default 2091 scaling driver for the supported processors 2092 passive 2093 Use intel_pstate as a scaling driver, but configure it 2094 to work with generic cpufreq governors (instead of 2095 enabling its internal governor). This mode cannot be 2096 used along with the hardware-managed P-states (HWP) 2097 feature. 2098 force 2099 Enable intel_pstate on systems that prohibit it by default 2100 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2101 instead of acpi-cpufreq may disable platform features, such 2102 as thermal controls and power capping, that rely on ACPI 2103 P-States information being indicated to OSPM and therefore 2104 should be used with caution. This option does not work with 2105 processors that aren't supported by the intel_pstate driver 2106 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2107 no_hwp 2108 Do not enable hardware P state control (HWP) 2109 if available. 2110 hwp_only 2111 Only load intel_pstate on systems which support 2112 hardware P state control (HWP) if available. 2113 support_acpi_ppc 2114 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2115 Description Table, specifies preferred power management 2116 profile as "Enterprise Server" or "Performance Server", 2117 then this feature is turned on by default. 2118 per_cpu_perf_limits 2119 Allow per-logical-CPU P-State performance control limits using 2120 cpufreq sysfs interface 2121 2122 intremap= [X86-64, Intel-IOMMU] 2123 on enable Interrupt Remapping (default) 2124 off disable Interrupt Remapping 2125 nosid disable Source ID checking 2126 no_x2apic_optout 2127 BIOS x2APIC opt-out request will be ignored 2128 nopost disable Interrupt Posting 2129 2130 iomem= Disable strict checking of access to MMIO memory 2131 strict regions from userspace. 2132 relaxed 2133 2134 iommu= [X86] 2135 off 2136 force 2137 noforce 2138 biomerge 2139 panic 2140 nopanic 2141 merge 2142 nomerge 2143 soft 2144 pt [X86] 2145 nopt [X86] 2146 nobypass [PPC/POWERNV] 2147 Disable IOMMU bypass, using IOMMU for PCI devices. 2148 2149 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices. 2150 Format: { "0" | "1" } 2151 0 - Try to allocate a 32-bit DMA address first, before 2152 falling back to the full range if needed. 2153 1 - Allocate directly from the full usable range, 2154 forcing Dual Address Cycle for PCI cards supporting 2155 greater than 32-bit addressing. 2156 2157 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour 2158 Format: { "0" | "1" } 2159 0 - Lazy mode. 2160 Request that DMA unmap operations use deferred 2161 invalidation of hardware TLBs, for increased 2162 throughput at the cost of reduced device isolation. 2163 Will fall back to strict mode if not supported by 2164 the relevant IOMMU driver. 2165 1 - Strict mode. 2166 DMA unmap operations invalidate IOMMU hardware TLBs 2167 synchronously. 2168 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2169 Note: on x86, strict mode specified via one of the 2170 legacy driver-specific options takes precedence. 2171 2172 iommu.passthrough= 2173 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 2174 Format: { "0" | "1" } 2175 0 - Use IOMMU translation for DMA. 2176 1 - Bypass the IOMMU for DMA. 2177 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2178 2179 io7= [HW] IO7 for Marvel-based Alpha systems 2180 See comment before marvel_specify_io7 in 2181 arch/alpha/kernel/core_marvel.c. 2182 2183 io_delay= [X86] I/O delay method 2184 0x80 2185 Standard port 0x80 based delay 2186 0xed 2187 Alternate port 0xed based delay (needed on some systems) 2188 udelay 2189 Simple two microseconds delay 2190 none 2191 No delay 2192 2193 ip= [IP_PNP] 2194 See Documentation/admin-guide/nfs/nfsroot.rst. 2195 2196 ipcmni_extend [KNL] Extend the maximum number of unique System V 2197 IPC identifiers from 32,768 to 16,777,216. 2198 2199 irqaffinity= [SMP] Set the default irq affinity mask 2200 The argument is a cpu list, as described above. 2201 2202 irqchip.gicv2_force_probe= 2203 [ARM, ARM64] 2204 Format: <bool> 2205 Force the kernel to look for the second 4kB page 2206 of a GICv2 controller even if the memory range 2207 exposed by the device tree is too small. 2208 2209 irqchip.gicv3_nolpi= 2210 [ARM, ARM64] 2211 Force the kernel to ignore the availability of 2212 LPIs (and by consequence ITSs). Intended for system 2213 that use the kernel as a bootloader, and thus want 2214 to let secondary kernels in charge of setting up 2215 LPIs. 2216 2217 irqchip.gicv3_pseudo_nmi= [ARM64] 2218 Enables support for pseudo-NMIs in the kernel. This 2219 requires the kernel to be built with 2220 CONFIG_ARM64_PSEUDO_NMI. 2221 2222 irqfixup [HW] 2223 When an interrupt is not handled search all handlers 2224 for it. Intended to get systems with badly broken 2225 firmware running. 2226 2227 irqpoll [HW] 2228 When an interrupt is not handled search all handlers 2229 for it. Also check all handlers each timer 2230 interrupt. Intended to get systems with badly broken 2231 firmware running. 2232 2233 isapnp= [ISAPNP] 2234 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2235 2236 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2237 [Deprecated - use cpusets instead] 2238 Format: [flag-list,]<cpu-list> 2239 2240 Specify one or more CPUs to isolate from disturbances 2241 specified in the flag list (default: domain): 2242 2243 nohz 2244 Disable the tick when a single task runs. 2245 2246 A residual 1Hz tick is offloaded to workqueues, which you 2247 need to affine to housekeeping through the global 2248 workqueue's affinity configured via the 2249 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2250 by using the 'domain' flag described below. 2251 2252 NOTE: by default the global workqueue runs on all CPUs, 2253 so to protect individual CPUs the 'cpumask' file has to 2254 be configured manually after bootup. 2255 2256 domain 2257 Isolate from the general SMP balancing and scheduling 2258 algorithms. Note that performing domain isolation this way 2259 is irreversible: it's not possible to bring back a CPU to 2260 the domains once isolated through isolcpus. It's strongly 2261 advised to use cpusets instead to disable scheduler load 2262 balancing through the "cpuset.sched_load_balance" file. 2263 It offers a much more flexible interface where CPUs can 2264 move in and out of an isolated set anytime. 2265 2266 You can move a process onto or off an "isolated" CPU via 2267 the CPU affinity syscalls or cpuset. 2268 <cpu number> begins at 0 and the maximum value is 2269 "number of CPUs in system - 1". 2270 2271 managed_irq 2272 2273 Isolate from being targeted by managed interrupts 2274 which have an interrupt mask containing isolated 2275 CPUs. The affinity of managed interrupts is 2276 handled by the kernel and cannot be changed via 2277 the /proc/irq/* interfaces. 2278 2279 This isolation is best effort and only effective 2280 if the automatically assigned interrupt mask of a 2281 device queue contains isolated and housekeeping 2282 CPUs. If housekeeping CPUs are online then such 2283 interrupts are directed to the housekeeping CPU 2284 so that IO submitted on the housekeeping CPU 2285 cannot disturb the isolated CPU. 2286 2287 If a queue's affinity mask contains only isolated 2288 CPUs then this parameter has no effect on the 2289 interrupt routing decision, though interrupts are 2290 only delivered when tasks running on those 2291 isolated CPUs submit IO. IO submitted on 2292 housekeeping CPUs has no influence on those 2293 queues. 2294 2295 The format of <cpu-list> is described above. 2296 2297 iucv= [HW,NET] 2298 2299 ivrs_ioapic [HW,X86-64] 2300 Provide an override to the IOAPIC-ID<->DEVICE-ID 2301 mapping provided in the IVRS ACPI table. 2302 By default, PCI segment is 0, and can be omitted. 2303 2304 For example, to map IOAPIC-ID decimal 10 to 2305 PCI segment 0x1 and PCI device 00:14.0, 2306 write the parameter as: 2307 ivrs_ioapic=10@0001:00:14.0 2308 2309 Deprecated formats: 2310 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2311 write the parameter as: 2312 ivrs_ioapic[10]=00:14.0 2313 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2314 PCI device 00:14.0 write the parameter as: 2315 ivrs_ioapic[10]=0001:00:14.0 2316 2317 ivrs_hpet [HW,X86-64] 2318 Provide an override to the HPET-ID<->DEVICE-ID 2319 mapping provided in the IVRS ACPI table. 2320 By default, PCI segment is 0, and can be omitted. 2321 2322 For example, to map HPET-ID decimal 10 to 2323 PCI segment 0x1 and PCI device 00:14.0, 2324 write the parameter as: 2325 ivrs_hpet=10@0001:00:14.0 2326 2327 Deprecated formats: 2328 * To map HPET-ID decimal 0 to PCI device 00:14.0 2329 write the parameter as: 2330 ivrs_hpet[0]=00:14.0 2331 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2332 PCI device 00:14.0 write the parameter as: 2333 ivrs_ioapic[10]=0001:00:14.0 2334 2335 ivrs_acpihid [HW,X86-64] 2336 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2337 mapping provided in the IVRS ACPI table. 2338 By default, PCI segment is 0, and can be omitted. 2339 2340 For example, to map UART-HID:UID AMD0020:0 to 2341 PCI segment 0x1 and PCI device ID 00:14.5, 2342 write the parameter as: 2343 ivrs_acpihid=AMD0020:0@0001:00:14.5 2344 2345 Deprecated formats: 2346 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2347 PCI device ID 00:14.5, write the parameter as: 2348 ivrs_acpihid[00:14.5]=AMD0020:0 2349 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2350 PCI device ID 00:14.5, write the parameter as: 2351 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2352 2353 js= [HW,JOY] Analog joystick 2354 See Documentation/input/joydev/joystick.rst. 2355 2356 nokaslr [KNL] 2357 When CONFIG_RANDOMIZE_BASE is set, this disables 2358 kernel and module base offset ASLR (Address Space 2359 Layout Randomization). 2360 2361 kasan_multi_shot 2362 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2363 report on every invalid memory access. Without this 2364 parameter KASAN will print report only for the first 2365 invalid access. 2366 2367 keepinitrd [HW,ARM] 2368 2369 kernelcore= [KNL,X86,IA-64,PPC] 2370 Format: nn[KMGTPE] | nn% | "mirror" 2371 This parameter specifies the amount of memory usable by 2372 the kernel for non-movable allocations. The requested 2373 amount is spread evenly throughout all nodes in the 2374 system as ZONE_NORMAL. The remaining memory is used for 2375 movable memory in its own zone, ZONE_MOVABLE. In the 2376 event, a node is too small to have both ZONE_NORMAL and 2377 ZONE_MOVABLE, kernelcore memory will take priority and 2378 other nodes will have a larger ZONE_MOVABLE. 2379 2380 ZONE_MOVABLE is used for the allocation of pages that 2381 may be reclaimed or moved by the page migration 2382 subsystem. Note that allocations like PTEs-from-HighMem 2383 still use the HighMem zone if it exists, and the Normal 2384 zone if it does not. 2385 2386 It is possible to specify the exact amount of memory in 2387 the form of "nn[KMGTPE]", a percentage of total system 2388 memory in the form of "nn%", or "mirror". If "mirror" 2389 option is specified, mirrored (reliable) memory is used 2390 for non-movable allocations and remaining memory is used 2391 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2392 are exclusive, so you cannot specify multiple forms. 2393 2394 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2395 Format: <Controller#>[,poll interval] 2396 The controller # is the number of the ehci usb debug 2397 port as it is probed via PCI. The poll interval is 2398 optional and is the number seconds in between 2399 each poll cycle to the debug port in case you need 2400 the functionality for interrupting the kernel with 2401 gdb or control-c on the dbgp connection. When 2402 not using this parameter you use sysrq-g to break into 2403 the kernel debugger. 2404 2405 kgdboc= [KGDB,HW] kgdb over consoles. 2406 Requires a tty driver that supports console polling, 2407 or a supported polling keyboard driver (non-usb). 2408 Serial only format: <serial_device>[,baud] 2409 keyboard only format: kbd 2410 keyboard and serial format: kbd,<serial_device>[,baud] 2411 Optional Kernel mode setting: 2412 kms, kbd format: kms,kbd 2413 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2414 2415 kgdboc_earlycon= [KGDB,HW] 2416 If the boot console provides the ability to read 2417 characters and can work in polling mode, you can use 2418 this parameter to tell kgdb to use it as a backend 2419 until the normal console is registered. Intended to 2420 be used together with the kgdboc parameter which 2421 specifies the normal console to transition to. 2422 2423 The name of the early console should be specified 2424 as the value of this parameter. Note that the name of 2425 the early console might be different than the tty 2426 name passed to kgdboc. It's OK to leave the value 2427 blank and the first boot console that implements 2428 read() will be picked. 2429 2430 kgdbwait [KGDB] Stop kernel execution and enter the 2431 kernel debugger at the earliest opportunity. 2432 2433 kmac= [MIPS] Korina ethernet MAC address. 2434 Configure the RouterBoard 532 series on-chip 2435 Ethernet adapter MAC address. 2436 2437 kmemleak= [KNL] Boot-time kmemleak enable/disable 2438 Valid arguments: on, off 2439 Default: on 2440 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2441 the default is off. 2442 2443 kprobe_event=[probe-list] 2444 [FTRACE] Add kprobe events and enable at boot time. 2445 The probe-list is a semicolon delimited list of probe 2446 definitions. Each definition is same as kprobe_events 2447 interface, but the parameters are comma delimited. 2448 For example, to add a kprobe event on vfs_read with 2449 arg1 and arg2, add to the command line; 2450 2451 kprobe_event=p,vfs_read,$arg1,$arg2 2452 2453 See also Documentation/trace/kprobetrace.rst "Kernel 2454 Boot Parameter" section. 2455 2456 kpti= [ARM64] Control page table isolation of user 2457 and kernel address spaces. 2458 Default: enabled on cores which need mitigation. 2459 0: force disabled 2460 1: force enabled 2461 2462 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 2463 CONFIG_KUNIT to be set to be fully enabled. The 2464 default value can be overridden via 2465 KUNIT_DEFAULT_ENABLED. 2466 Default is 1 (enabled) 2467 2468 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2469 Default is 0 (don't ignore, but inject #GP) 2470 2471 kvm.eager_page_split= 2472 [KVM,X86] Controls whether or not KVM will try to 2473 proactively split all huge pages during dirty logging. 2474 Eager page splitting reduces interruptions to vCPU 2475 execution by eliminating the write-protection faults 2476 and MMU lock contention that would otherwise be 2477 required to split huge pages lazily. 2478 2479 VM workloads that rarely perform writes or that write 2480 only to a small region of VM memory may benefit from 2481 disabling eager page splitting to allow huge pages to 2482 still be used for reads. 2483 2484 The behavior of eager page splitting depends on whether 2485 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 2486 disabled, all huge pages in a memslot will be eagerly 2487 split when dirty logging is enabled on that memslot. If 2488 enabled, eager page splitting will be performed during 2489 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 2490 cleared. 2491 2492 Eager page splitting is only supported when kvm.tdp_mmu=Y. 2493 2494 Default is Y (on). 2495 2496 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2497 Default is false (don't support). 2498 2499 kvm.nx_huge_pages= 2500 [KVM] Controls the software workaround for the 2501 X86_BUG_ITLB_MULTIHIT bug. 2502 force : Always deploy workaround. 2503 off : Never deploy workaround. 2504 auto : Deploy workaround based on the presence of 2505 X86_BUG_ITLB_MULTIHIT. 2506 2507 Default is 'auto'. 2508 2509 If the software workaround is enabled for the host, 2510 guests do need not to enable it for nested guests. 2511 2512 kvm.nx_huge_pages_recovery_ratio= 2513 [KVM] Controls how many 4KiB pages are periodically zapped 2514 back to huge pages. 0 disables the recovery, otherwise if 2515 the value is N KVM will zap 1/Nth of the 4KiB pages every 2516 period (see below). The default is 60. 2517 2518 kvm.nx_huge_pages_recovery_period_ms= 2519 [KVM] Controls the time period at which KVM zaps 4KiB pages 2520 back to huge pages. If the value is a non-zero N, KVM will 2521 zap a portion (see ratio above) of the pages every N msecs. 2522 If the value is 0 (the default), KVM will pick a period based 2523 on the ratio, such that a page is zapped after 1 hour on average. 2524 2525 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2526 Default is 1 (enabled) 2527 2528 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2529 for all guests. 2530 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2531 2532 kvm-arm.mode= 2533 [KVM,ARM] Select one of KVM/arm64's modes of operation. 2534 2535 none: Forcefully disable KVM. 2536 2537 nvhe: Standard nVHE-based mode, without support for 2538 protected guests. 2539 2540 protected: nVHE-based mode with support for guests whose 2541 state is kept private from the host. 2542 2543 Defaults to VHE/nVHE based on hardware support. Setting 2544 mode to "protected" will disable kexec and hibernation 2545 for the host. 2546 2547 kvm-arm.vgic_v3_group0_trap= 2548 [KVM,ARM] Trap guest accesses to GICv3 group-0 2549 system registers 2550 2551 kvm-arm.vgic_v3_group1_trap= 2552 [KVM,ARM] Trap guest accesses to GICv3 group-1 2553 system registers 2554 2555 kvm-arm.vgic_v3_common_trap= 2556 [KVM,ARM] Trap guest accesses to GICv3 common 2557 system registers 2558 2559 kvm-arm.vgic_v4_enable= 2560 [KVM,ARM] Allow use of GICv4 for direct injection of 2561 LPIs. 2562 2563 kvm_cma_resv_ratio=n [PPC] 2564 Reserves given percentage from system memory area for 2565 contiguous memory allocation for KVM hash pagetable 2566 allocation. 2567 By default it reserves 5% of total system memory. 2568 Format: <integer> 2569 Default: 5 2570 2571 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2572 (virtualized MMU) support on capable Intel chips. 2573 Default is 1 (enabled) 2574 2575 kvm-intel.emulate_invalid_guest_state= 2576 [KVM,Intel] Disable emulation of invalid guest state. 2577 Ignored if kvm-intel.enable_unrestricted_guest=1, as 2578 guest state is never invalid for unrestricted guests. 2579 This param doesn't apply to nested guests (L2), as KVM 2580 never emulates invalid L2 guest state. 2581 Default is 1 (enabled) 2582 2583 kvm-intel.flexpriority= 2584 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2585 Default is 1 (enabled) 2586 2587 kvm-intel.nested= 2588 [KVM,Intel] Enable VMX nesting (nVMX). 2589 Default is 0 (disabled) 2590 2591 kvm-intel.unrestricted_guest= 2592 [KVM,Intel] Disable unrestricted guest feature 2593 (virtualized real and unpaged mode) on capable 2594 Intel chips. Default is 1 (enabled) 2595 2596 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2597 CVE-2018-3620. 2598 2599 Valid arguments: never, cond, always 2600 2601 always: L1D cache flush on every VMENTER. 2602 cond: Flush L1D on VMENTER only when the code between 2603 VMEXIT and VMENTER can leak host memory. 2604 never: Disables the mitigation 2605 2606 Default is cond (do L1 cache flush in specific instances) 2607 2608 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2609 feature (tagged TLBs) on capable Intel chips. 2610 Default is 1 (enabled) 2611 2612 l1d_flush= [X86,INTEL] 2613 Control mitigation for L1D based snooping vulnerability. 2614 2615 Certain CPUs are vulnerable to an exploit against CPU 2616 internal buffers which can forward information to a 2617 disclosure gadget under certain conditions. 2618 2619 In vulnerable processors, the speculatively 2620 forwarded data can be used in a cache side channel 2621 attack, to access data to which the attacker does 2622 not have direct access. 2623 2624 This parameter controls the mitigation. The 2625 options are: 2626 2627 on - enable the interface for the mitigation 2628 2629 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2630 affected CPUs 2631 2632 The kernel PTE inversion protection is unconditionally 2633 enabled and cannot be disabled. 2634 2635 full 2636 Provides all available mitigations for the 2637 L1TF vulnerability. Disables SMT and 2638 enables all mitigations in the 2639 hypervisors, i.e. unconditional L1D flush. 2640 2641 SMT control and L1D flush control via the 2642 sysfs interface is still possible after 2643 boot. Hypervisors will issue a warning 2644 when the first VM is started in a 2645 potentially insecure configuration, 2646 i.e. SMT enabled or L1D flush disabled. 2647 2648 full,force 2649 Same as 'full', but disables SMT and L1D 2650 flush runtime control. Implies the 2651 'nosmt=force' command line option. 2652 (i.e. sysfs control of SMT is disabled.) 2653 2654 flush 2655 Leaves SMT enabled and enables the default 2656 hypervisor mitigation, i.e. conditional 2657 L1D flush. 2658 2659 SMT control and L1D flush control via the 2660 sysfs interface is still possible after 2661 boot. Hypervisors will issue a warning 2662 when the first VM is started in a 2663 potentially insecure configuration, 2664 i.e. SMT enabled or L1D flush disabled. 2665 2666 flush,nosmt 2667 2668 Disables SMT and enables the default 2669 hypervisor mitigation. 2670 2671 SMT control and L1D flush control via the 2672 sysfs interface is still possible after 2673 boot. Hypervisors will issue a warning 2674 when the first VM is started in a 2675 potentially insecure configuration, 2676 i.e. SMT enabled or L1D flush disabled. 2677 2678 flush,nowarn 2679 Same as 'flush', but hypervisors will not 2680 warn when a VM is started in a potentially 2681 insecure configuration. 2682 2683 off 2684 Disables hypervisor mitigations and doesn't 2685 emit any warnings. 2686 It also drops the swap size and available 2687 RAM limit restriction on both hypervisor and 2688 bare metal. 2689 2690 Default is 'flush'. 2691 2692 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2693 2694 l2cr= [PPC] 2695 2696 l3cr= [PPC] 2697 2698 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2699 disabled it. 2700 2701 lapic= [X86,APIC] Do not use TSC deadline 2702 value for LAPIC timer one-shot implementation. Default 2703 back to the programmable timer unit in the LAPIC. 2704 Format: notscdeadline 2705 2706 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2707 in C2 power state. 2708 2709 libata.dma= [LIBATA] DMA control 2710 libata.dma=0 Disable all PATA and SATA DMA 2711 libata.dma=1 PATA and SATA Disk DMA only 2712 libata.dma=2 ATAPI (CDROM) DMA only 2713 libata.dma=4 Compact Flash DMA only 2714 Combinations also work, so libata.dma=3 enables DMA 2715 for disks and CDROMs, but not CFs. 2716 2717 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2718 libata.ignore_hpa=0 keep BIOS limits (default) 2719 libata.ignore_hpa=1 ignore limits, using full disk 2720 2721 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2722 when set. 2723 Format: <int> 2724 2725 libata.force= [LIBATA] Force configurations. The format is a comma- 2726 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 2727 PORT and DEVICE are decimal numbers matching port, link 2728 or device. Basically, it matches the ATA ID string 2729 printed on console by libata. If the whole ID part is 2730 omitted, the last PORT and DEVICE values are used. If 2731 ID hasn't been specified yet, the configuration applies 2732 to all ports, links and devices. 2733 2734 If only DEVICE is omitted, the parameter applies to 2735 the port and all links and devices behind it. DEVICE 2736 number of 0 either selects the first device or the 2737 first fan-out link behind PMP device. It does not 2738 select the host link. DEVICE number of 15 selects the 2739 host link and device attached to it. 2740 2741 The VAL specifies the configuration to force. As long 2742 as there is no ambiguity, shortcut notation is allowed. 2743 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2744 The following configurations can be forced. 2745 2746 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2747 Any ID with matching PORT is used. 2748 2749 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2750 2751 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2752 udma[/][16,25,33,44,66,100,133] notation is also 2753 allowed. 2754 2755 * nohrst, nosrst, norst: suppress hard, soft and both 2756 resets. 2757 2758 * rstonce: only attempt one reset during hot-unplug 2759 link recovery. 2760 2761 * [no]dbdelay: Enable or disable the extra 200ms delay 2762 before debouncing a link PHY and device presence 2763 detection. 2764 2765 * [no]ncq: Turn on or off NCQ. 2766 2767 * [no]ncqtrim: Enable or disable queued DSM TRIM. 2768 2769 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 2770 2771 * [no]trim: Enable or disable (unqueued) TRIM. 2772 2773 * trim_zero: Indicate that TRIM command zeroes data. 2774 2775 * max_trim_128m: Set 128M maximum trim size limit. 2776 2777 * [no]dma: Turn on or off DMA transfers. 2778 2779 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 2780 2781 * atapi_mod16_dma: Enable the use of ATAPI DMA for 2782 commands that are not a multiple of 16 bytes. 2783 2784 * [no]dmalog: Enable or disable the use of the 2785 READ LOG DMA EXT command to access logs. 2786 2787 * [no]iddevlog: Enable or disable access to the 2788 identify device data log. 2789 2790 * [no]logdir: Enable or disable access to the general 2791 purpose log directory. 2792 2793 * max_sec_128: Set transfer size limit to 128 sectors. 2794 2795 * max_sec_1024: Set or clear transfer size limit to 2796 1024 sectors. 2797 2798 * max_sec_lba48: Set or clear transfer size limit to 2799 65535 sectors. 2800 2801 * [no]lpm: Enable or disable link power management. 2802 2803 * [no]setxfer: Indicate if transfer speed mode setting 2804 should be skipped. 2805 2806 * dump_id: Dump IDENTIFY data. 2807 2808 * disable: Disable this device. 2809 2810 If there are multiple matching configurations changing 2811 the same attribute, the last one is used. 2812 2813 load_ramdisk= [RAM] [Deprecated] 2814 2815 lockd.nlm_grace_period=P [NFS] Assign grace period. 2816 Format: <integer> 2817 2818 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2819 Format: <integer> 2820 2821 lockd.nlm_timeout=T [NFS] Assign timeout value. 2822 Format: <integer> 2823 2824 lockd.nlm_udpport=M [NFS] Assign UDP port. 2825 Format: <integer> 2826 2827 lockdown= [SECURITY] 2828 { integrity | confidentiality } 2829 Enable the kernel lockdown feature. If set to 2830 integrity, kernel features that allow userland to 2831 modify the running kernel are disabled. If set to 2832 confidentiality, kernel features that allow userland 2833 to extract confidential information from the kernel 2834 are also disabled. 2835 2836 locktorture.nreaders_stress= [KNL] 2837 Set the number of locking read-acquisition kthreads. 2838 Defaults to being automatically set based on the 2839 number of online CPUs. 2840 2841 locktorture.nwriters_stress= [KNL] 2842 Set the number of locking write-acquisition kthreads. 2843 2844 locktorture.onoff_holdoff= [KNL] 2845 Set time (s) after boot for CPU-hotplug testing. 2846 2847 locktorture.onoff_interval= [KNL] 2848 Set time (s) between CPU-hotplug operations, or 2849 zero to disable CPU-hotplug testing. 2850 2851 locktorture.shuffle_interval= [KNL] 2852 Set task-shuffle interval (jiffies). Shuffling 2853 tasks allows some CPUs to go into dyntick-idle 2854 mode during the locktorture test. 2855 2856 locktorture.shutdown_secs= [KNL] 2857 Set time (s) after boot system shutdown. This 2858 is useful for hands-off automated testing. 2859 2860 locktorture.stat_interval= [KNL] 2861 Time (s) between statistics printk()s. 2862 2863 locktorture.stutter= [KNL] 2864 Time (s) to stutter testing, for example, 2865 specifying five seconds causes the test to run for 2866 five seconds, wait for five seconds, and so on. 2867 This tests the locking primitive's ability to 2868 transition abruptly to and from idle. 2869 2870 locktorture.torture_type= [KNL] 2871 Specify the locking implementation to test. 2872 2873 locktorture.verbose= [KNL] 2874 Enable additional printk() statements. 2875 2876 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2877 Format: <irq> 2878 2879 loglevel= All Kernel Messages with a loglevel smaller than the 2880 console loglevel will be printed to the console. It can 2881 also be changed with klogd or other programs. The 2882 loglevels are defined as follows: 2883 2884 0 (KERN_EMERG) system is unusable 2885 1 (KERN_ALERT) action must be taken immediately 2886 2 (KERN_CRIT) critical conditions 2887 3 (KERN_ERR) error conditions 2888 4 (KERN_WARNING) warning conditions 2889 5 (KERN_NOTICE) normal but significant condition 2890 6 (KERN_INFO) informational 2891 7 (KERN_DEBUG) debug-level messages 2892 2893 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2894 in bytes. n must be a power of two and greater 2895 than the minimal size. The minimal size is defined 2896 by LOG_BUF_SHIFT kernel config parameter. There is 2897 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2898 that allows to increase the default size depending on 2899 the number of CPUs. See init/Kconfig for more details. 2900 2901 logo.nologo [FB] Disables display of the built-in Linux logo. 2902 This may be used to provide more screen space for 2903 kernel log messages and is useful when debugging 2904 kernel boot problems. 2905 2906 lp=0 [LP] Specify parallel ports to use, e.g, 2907 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2908 lp=reset first parallel port). 'lp=0' disables the 2909 lp=auto printer driver. 'lp=reset' (which can be 2910 specified in addition to the ports) causes 2911 attached printers to be reset. Using 2912 lp=port1,port2,... specifies the parallel ports 2913 to associate lp devices with, starting with 2914 lp0. A port specification may be 'none' to skip 2915 that lp device, or a parport name such as 2916 'parport0'. Specifying 'lp=auto' instead of a 2917 port specification list means that device IDs 2918 from each port should be examined, to see if 2919 an IEEE 1284-compliant printer is attached; if 2920 so, the driver will manage that printer. 2921 See also header of drivers/char/lp.c. 2922 2923 lpj=n [KNL] 2924 Sets loops_per_jiffy to given constant, thus avoiding 2925 time-consuming boot-time autodetection (up to 250 ms per 2926 CPU). 0 enables autodetection (default). To determine 2927 the correct value for your kernel, boot with normal 2928 autodetection and see what value is printed. Note that 2929 on SMP systems the preset will be applied to all CPUs, 2930 which is likely to cause problems if your CPUs need 2931 significantly divergent settings. An incorrect value 2932 will cause delays in the kernel to be wrong, leading to 2933 unpredictable I/O errors and other breakage. Although 2934 unlikely, in the extreme case this might damage your 2935 hardware. 2936 2937 ltpc= [NET] 2938 Format: <io>,<irq>,<dma> 2939 2940 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2941 2942 lsm=lsm1,...,lsmN 2943 [SECURITY] Choose order of LSM initialization. This 2944 overrides CONFIG_LSM, and the "security=" parameter. 2945 2946 machvec= [IA-64] Force the use of a particular machine-vector 2947 (machvec) in a generic kernel. 2948 Example: machvec=hpzx1 2949 2950 machtype= [Loongson] Share the same kernel image file between 2951 different yeeloong laptops. 2952 Example: machtype=lemote-yeeloong-2f-7inch 2953 2954 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater 2955 than or equal to this physical address is ignored. 2956 2957 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2958 will bring up during bootup. maxcpus=n : n >= 0 limits 2959 the kernel to bring up 'n' processors. Surely after 2960 bootup you can bring up the other plugged cpu by executing 2961 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2962 only takes effect during system bootup. 2963 While n=0 is a special case, it is equivalent to "nosmp", 2964 which also disables the IO APIC. 2965 2966 max_loop= [LOOP] The number of loop block devices that get 2967 (loop.max_loop) unconditionally pre-created at init time. The default 2968 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2969 of statically allocating a predefined number, loop 2970 devices can be requested on-demand with the 2971 /dev/loop-control interface. 2972 2973 mce [X86-32] Machine Check Exception 2974 2975 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2976 2977 md= [HW] RAID subsystems devices and level 2978 See Documentation/admin-guide/md.rst. 2979 2980 mdacon= [MDA] 2981 Format: <first>,<last> 2982 Specifies range of consoles to be captured by the MDA. 2983 2984 mds= [X86,INTEL] 2985 Control mitigation for the Micro-architectural Data 2986 Sampling (MDS) vulnerability. 2987 2988 Certain CPUs are vulnerable to an exploit against CPU 2989 internal buffers which can forward information to a 2990 disclosure gadget under certain conditions. 2991 2992 In vulnerable processors, the speculatively 2993 forwarded data can be used in a cache side channel 2994 attack, to access data to which the attacker does 2995 not have direct access. 2996 2997 This parameter controls the MDS mitigation. The 2998 options are: 2999 3000 full - Enable MDS mitigation on vulnerable CPUs 3001 full,nosmt - Enable MDS mitigation and disable 3002 SMT on vulnerable CPUs 3003 off - Unconditionally disable MDS mitigation 3004 3005 On TAA-affected machines, mds=off can be prevented by 3006 an active TAA mitigation as both vulnerabilities are 3007 mitigated with the same mechanism so in order to disable 3008 this mitigation, you need to specify tsx_async_abort=off 3009 too. 3010 3011 Not specifying this option is equivalent to 3012 mds=full. 3013 3014 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3015 3016 mem=nn[KMG] [HEXAGON] Set the memory size. 3017 Must be specified, otherwise memory size will be 0. 3018 3019 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 3020 Amount of memory to be used in cases as follows: 3021 3022 1 for test; 3023 2 when the kernel is not able to see the whole system memory; 3024 3 memory that lies after 'mem=' boundary is excluded from 3025 the hypervisor, then assigned to KVM guests. 3026 4 to limit the memory available for kdump kernel. 3027 3028 [ARC,MICROBLAZE] - the limit applies only to low memory, 3029 high memory is not affected. 3030 3031 [ARM64] - only limits memory covered by the linear 3032 mapping. The NOMAP regions are not affected. 3033 3034 [X86] Work as limiting max address. Use together 3035 with memmap= to avoid physical address space collisions. 3036 Without memmap= PCI devices could be placed at addresses 3037 belonging to unused RAM. 3038 3039 Note that this only takes effects during boot time since 3040 in above case 3, memory may need be hot added after boot 3041 if system memory of hypervisor is not sufficient. 3042 3043 mem=nn[KMG]@ss[KMG] 3044 [ARM,MIPS] - override the memory layout reported by 3045 firmware. 3046 Define a memory region of size nn[KMG] starting at 3047 ss[KMG]. 3048 Multiple different regions can be specified with 3049 multiple mem= parameters on the command line. 3050 3051 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3052 memory. 3053 3054 memblock=debug [KNL] Enable memblock debug messages. 3055 3056 memchunk=nn[KMG] 3057 [KNL,SH] Allow user to override the default size for 3058 per-device physically contiguous DMA buffers. 3059 3060 memhp_default_state=online/offline 3061 [KNL] Set the initial state for the memory hotplug 3062 onlining policy. If not specified, the default value is 3063 set according to the 3064 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 3065 option. 3066 See Documentation/admin-guide/mm/memory-hotplug.rst. 3067 3068 memmap=exactmap [KNL,X86] Enable setting of an exact 3069 E820 memory map, as specified by the user. 3070 Such memmap=exactmap lines can be constructed based on 3071 BIOS output or other requirements. See the memmap=nn@ss 3072 option description. 3073 3074 memmap=nn[KMG]@ss[KMG] 3075 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory. 3076 Region of memory to be used is from ss to ss+nn. 3077 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3078 which limits max address to nn[KMG]. 3079 Multiple different regions can be specified, 3080 comma delimited. 3081 Example: 3082 memmap=100M@2G,100M#3G,1G!1024G 3083 3084 memmap=nn[KMG]#ss[KMG] 3085 [KNL,ACPI] Mark specific memory as ACPI data. 3086 Region of memory to be marked is from ss to ss+nn. 3087 3088 memmap=nn[KMG]$ss[KMG] 3089 [KNL,ACPI] Mark specific memory as reserved. 3090 Region of memory to be reserved is from ss to ss+nn. 3091 Example: Exclude memory from 0x18690000-0x1869ffff 3092 memmap=64K$0x18690000 3093 or 3094 memmap=0x10000$0x18690000 3095 Some bootloaders may need an escape character before '$', 3096 like Grub2, otherwise '$' and the following number 3097 will be eaten. 3098 3099 memmap=nn[KMG]!ss[KMG] 3100 [KNL,X86] Mark specific memory as protected. 3101 Region of memory to be used, from ss to ss+nn. 3102 The memory region may be marked as e820 type 12 (0xc) 3103 and is NVDIMM or ADR memory. 3104 3105 memmap=<size>%<offset>-<oldtype>+<newtype> 3106 [KNL,ACPI] Convert memory within the specified region 3107 from <oldtype> to <newtype>. If "-<oldtype>" is left 3108 out, the whole region will be marked as <newtype>, 3109 even if previously unavailable. If "+<newtype>" is left 3110 out, matching memory will be removed. Types are 3111 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3112 3 = ACPI, 12 = PRAM. 3113 3114 memory_corruption_check=0/1 [X86] 3115 Some BIOSes seem to corrupt the first 64k of 3116 memory when doing things like suspend/resume. 3117 Setting this option will scan the memory 3118 looking for corruption. Enabling this will 3119 both detect corruption and prevent the kernel 3120 from using the memory being corrupted. 3121 However, its intended as a diagnostic tool; if 3122 repeatable BIOS-originated corruption always 3123 affects the same memory, you can use memmap= 3124 to prevent the kernel from using that memory. 3125 3126 memory_corruption_check_size=size [X86] 3127 By default it checks for corruption in the low 3128 64k, making this memory unavailable for normal 3129 use. Use this parameter to scan for 3130 corruption in more or less memory. 3131 3132 memory_corruption_check_period=seconds [X86] 3133 By default it checks for corruption every 60 3134 seconds. Use this parameter to check at some 3135 other rate. 0 disables periodic checking. 3136 3137 memory_hotplug.memmap_on_memory 3138 [KNL,X86,ARM] Boolean flag to enable this feature. 3139 Format: {on | off (default)} 3140 When enabled, runtime hotplugged memory will 3141 allocate its internal metadata (struct pages, 3142 those vmemmap pages cannot be optimized even 3143 if hugetlb_free_vmemmap is enabled) from the 3144 hotadded memory which will allow to hotadd a 3145 lot of memory without requiring additional 3146 memory to do so. 3147 This feature is disabled by default because it 3148 has some implication on large (e.g. GB) 3149 allocations in some configurations (e.g. small 3150 memory blocks). 3151 The state of the flag can be read in 3152 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3153 Note that even when enabled, there are a few cases where 3154 the feature is not effective. 3155 3156 memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest 3157 Format: <integer> 3158 default : 0 <disable> 3159 Specifies the number of memtest passes to be 3160 performed. Each pass selects another test 3161 pattern from a given set of patterns. Memtest 3162 fills the memory with this pattern, validates 3163 memory contents and reserves bad memory 3164 regions that are detected. 3165 3166 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 3167 Valid arguments: on, off 3168 Default (depends on kernel configuration option): 3169 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 3170 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 3171 mem_encrypt=on: Activate SME 3172 mem_encrypt=off: Do not activate SME 3173 3174 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 3175 for details on when memory encryption can be activated. 3176 3177 mem_sleep_default= [SUSPEND] Default system suspend mode: 3178 s2idle - Suspend-To-Idle 3179 shallow - Power-On Suspend or equivalent (if supported) 3180 deep - Suspend-To-RAM or equivalent (if supported) 3181 See Documentation/admin-guide/pm/sleep-states.rst. 3182 3183 meye.*= [HW] Set MotionEye Camera parameters 3184 See Documentation/admin-guide/media/meye.rst. 3185 3186 mfgpt_irq= [IA-32] Specify the IRQ to use for the 3187 Multi-Function General Purpose Timers on AMD Geode 3188 platforms. 3189 3190 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 3191 the BIOS has incorrectly applied a workaround. TinyBIOS 3192 version 0.98 is known to be affected, 0.99 fixes the 3193 problem by letting the user disable the workaround. 3194 3195 mga= [HW,DRM] 3196 3197 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this 3198 physical address is ignored. 3199 3200 mini2440= [ARM,HW,KNL] 3201 Format:[0..2][b][c][t] 3202 Default: "0tb" 3203 MINI2440 configuration specification: 3204 0 - The attached screen is the 3.5" TFT 3205 1 - The attached screen is the 7" TFT 3206 2 - The VGA Shield is attached (1024x768) 3207 Leaving out the screen size parameter will not load 3208 the TFT driver, and the framebuffer will be left 3209 unconfigured. 3210 b - Enable backlight. The TFT backlight pin will be 3211 linked to the kernel VESA blanking code and a GPIO 3212 LED. This parameter is not necessary when using the 3213 VGA shield. 3214 c - Enable the s3c camera interface. 3215 t - Reserved for enabling touchscreen support. The 3216 touchscreen support is not enabled in the mainstream 3217 kernel as of 2.6.30, a preliminary port can be found 3218 in the "bleeding edge" mini2440 support kernel at 3219 https://repo.or.cz/w/linux-2.6/mini2440.git 3220 3221 mitigations= 3222 [X86,PPC,S390,ARM64] Control optional mitigations for 3223 CPU vulnerabilities. This is a set of curated, 3224 arch-independent options, each of which is an 3225 aggregation of existing arch-specific options. 3226 3227 off 3228 Disable all optional CPU mitigations. This 3229 improves system performance, but it may also 3230 expose users to several CPU vulnerabilities. 3231 Equivalent to: nopti [X86,PPC] 3232 if nokaslr then kpti=0 [ARM64] 3233 nospectre_v1 [X86,PPC] 3234 nobp=0 [S390] 3235 nospectre_v2 [X86,PPC,S390,ARM64] 3236 spectre_v2_user=off [X86] 3237 spec_store_bypass_disable=off [X86,PPC] 3238 ssbd=force-off [ARM64] 3239 nospectre_bhb [ARM64] 3240 l1tf=off [X86] 3241 mds=off [X86] 3242 tsx_async_abort=off [X86] 3243 kvm.nx_huge_pages=off [X86] 3244 srbds=off [X86,INTEL] 3245 no_entry_flush [PPC] 3246 no_uaccess_flush [PPC] 3247 mmio_stale_data=off [X86] 3248 retbleed=off [X86] 3249 3250 Exceptions: 3251 This does not have any effect on 3252 kvm.nx_huge_pages when 3253 kvm.nx_huge_pages=force. 3254 3255 auto (default) 3256 Mitigate all CPU vulnerabilities, but leave SMT 3257 enabled, even if it's vulnerable. This is for 3258 users who don't want to be surprised by SMT 3259 getting disabled across kernel upgrades, or who 3260 have other ways of avoiding SMT-based attacks. 3261 Equivalent to: (default behavior) 3262 3263 auto,nosmt 3264 Mitigate all CPU vulnerabilities, disabling SMT 3265 if needed. This is for users who always want to 3266 be fully mitigated, even if it means losing SMT. 3267 Equivalent to: l1tf=flush,nosmt [X86] 3268 mds=full,nosmt [X86] 3269 tsx_async_abort=full,nosmt [X86] 3270 mmio_stale_data=full,nosmt [X86] 3271 retbleed=auto,nosmt [X86] 3272 3273 mminit_loglevel= 3274 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 3275 parameter allows control of the logging verbosity for 3276 the additional memory initialisation checks. A value 3277 of 0 disables mminit logging and a level of 4 will 3278 log everything. Information is printed at KERN_DEBUG 3279 so loglevel=8 may also need to be specified. 3280 3281 mmio_stale_data= 3282 [X86,INTEL] Control mitigation for the Processor 3283 MMIO Stale Data vulnerabilities. 3284 3285 Processor MMIO Stale Data is a class of 3286 vulnerabilities that may expose data after an MMIO 3287 operation. Exposed data could originate or end in 3288 the same CPU buffers as affected by MDS and TAA. 3289 Therefore, similar to MDS and TAA, the mitigation 3290 is to clear the affected CPU buffers. 3291 3292 This parameter controls the mitigation. The 3293 options are: 3294 3295 full - Enable mitigation on vulnerable CPUs 3296 3297 full,nosmt - Enable mitigation and disable SMT on 3298 vulnerable CPUs. 3299 3300 off - Unconditionally disable mitigation 3301 3302 On MDS or TAA affected machines, 3303 mmio_stale_data=off can be prevented by an active 3304 MDS or TAA mitigation as these vulnerabilities are 3305 mitigated with the same mechanism so in order to 3306 disable this mitigation, you need to specify 3307 mds=off and tsx_async_abort=off too. 3308 3309 Not specifying this option is equivalent to 3310 mmio_stale_data=full. 3311 3312 For details see: 3313 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 3314 3315 module.async_probe=<bool> 3316 [KNL] When set to true, modules will use async probing 3317 by default. To enable/disable async probing for a 3318 specific module, use the module specific control that 3319 is documented under <module>.async_probe. When both 3320 module.async_probe and <module>.async_probe are 3321 specified, <module>.async_probe takes precedence for 3322 the specific module. 3323 3324 module.sig_enforce 3325 [KNL] When CONFIG_MODULE_SIG is set, this means that 3326 modules without (valid) signatures will fail to load. 3327 Note that if CONFIG_MODULE_SIG_FORCE is set, that 3328 is always true, so this option does nothing. 3329 3330 module_blacklist= [KNL] Do not load a comma-separated list of 3331 modules. Useful for debugging problem modules. 3332 3333 mousedev.tap_time= 3334 [MOUSE] Maximum time between finger touching and 3335 leaving touchpad surface for touch to be considered 3336 a tap and be reported as a left button click (for 3337 touchpads working in absolute mode only). 3338 Format: <msecs> 3339 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 3340 reporting absolute coordinates, such as tablets 3341 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 3342 reporting absolute coordinates, such as tablets 3343 3344 movablecore= [KNL,X86,IA-64,PPC] 3345 Format: nn[KMGTPE] | nn% 3346 This parameter is the complement to kernelcore=, it 3347 specifies the amount of memory used for migratable 3348 allocations. If both kernelcore and movablecore is 3349 specified, then kernelcore will be at *least* the 3350 specified value but may be more. If movablecore on its 3351 own is specified, the administrator must be careful 3352 that the amount of memory usable for all allocations 3353 is not too small. 3354 3355 movable_node [KNL] Boot-time switch to make hotplugable memory 3356 NUMA nodes to be movable. This means that the memory 3357 of such nodes will be usable only for movable 3358 allocations which rules out almost all kernel 3359 allocations. Use with caution! 3360 3361 MTD_Partition= [MTD] 3362 Format: <name>,<region-number>,<size>,<offset> 3363 3364 MTD_Region= [MTD] Format: 3365 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 3366 3367 mtdparts= [MTD] 3368 See drivers/mtd/parsers/cmdlinepart.c 3369 3370 mtdset= [ARM] 3371 ARM/S3C2412 JIVE boot control 3372 3373 See arch/arm/mach-s3c/mach-jive.c 3374 3375 mtouchusb.raw_coordinates= 3376 [HW] Make the MicroTouch USB driver use raw coordinates 3377 ('y', default) or cooked coordinates ('n') 3378 3379 mtrr_chunk_size=nn[KMG] [X86] 3380 used for mtrr cleanup. It is largest continuous chunk 3381 that could hold holes aka. UC entries. 3382 3383 mtrr_gran_size=nn[KMG] [X86] 3384 Used for mtrr cleanup. It is granularity of mtrr block. 3385 Default is 1. 3386 Large value could prevent small alignment from 3387 using up MTRRs. 3388 3389 mtrr_spare_reg_nr=n [X86] 3390 Format: <integer> 3391 Range: 0,7 : spare reg number 3392 Default : 1 3393 Used for mtrr cleanup. It is spare mtrr entries number. 3394 Set to 2 or more if your graphical card needs more. 3395 3396 multitce=off [PPC] This parameter disables the use of the pSeries 3397 firmware feature for updating multiple TCE entries 3398 at a time. 3399 3400 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 3401 3402 netdev= [NET] Network devices parameters 3403 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 3404 Note that mem_start is often overloaded to mean 3405 something different and driver-specific. 3406 This usage is only documented in each driver source 3407 file if at all. 3408 3409 netpoll.carrier_timeout= 3410 [NET] Specifies amount of time (in seconds) that 3411 netpoll should wait for a carrier. By default netpoll 3412 waits 4 seconds. 3413 3414 nf_conntrack.acct= 3415 [NETFILTER] Enable connection tracking flow accounting 3416 0 to disable accounting 3417 1 to enable accounting 3418 Default value is 0. 3419 3420 nfsaddrs= [NFS] Deprecated. Use ip= instead. 3421 See Documentation/admin-guide/nfs/nfsroot.rst. 3422 3423 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 3424 See Documentation/admin-guide/nfs/nfsroot.rst. 3425 3426 nfsrootdebug [NFS] enable nfsroot debugging messages. 3427 See Documentation/admin-guide/nfs/nfsroot.rst. 3428 3429 nfs.callback_nr_threads= 3430 [NFSv4] set the total number of threads that the 3431 NFS client will assign to service NFSv4 callback 3432 requests. 3433 3434 nfs.callback_tcpport= 3435 [NFS] set the TCP port on which the NFSv4 callback 3436 channel should listen. 3437 3438 nfs.cache_getent= 3439 [NFS] sets the pathname to the program which is used 3440 to update the NFS client cache entries. 3441 3442 nfs.cache_getent_timeout= 3443 [NFS] sets the timeout after which an attempt to 3444 update a cache entry is deemed to have failed. 3445 3446 nfs.idmap_cache_timeout= 3447 [NFS] set the maximum lifetime for idmapper cache 3448 entries. 3449 3450 nfs.enable_ino64= 3451 [NFS] enable 64-bit inode numbers. 3452 If zero, the NFS client will fake up a 32-bit inode 3453 number for the readdir() and stat() syscalls instead 3454 of returning the full 64-bit number. 3455 The default is to return 64-bit inode numbers. 3456 3457 nfs.max_session_cb_slots= 3458 [NFSv4.1] Sets the maximum number of session 3459 slots the client will assign to the callback 3460 channel. This determines the maximum number of 3461 callbacks the client will process in parallel for 3462 a particular server. 3463 3464 nfs.max_session_slots= 3465 [NFSv4.1] Sets the maximum number of session slots 3466 the client will attempt to negotiate with the server. 3467 This limits the number of simultaneous RPC requests 3468 that the client can send to the NFSv4.1 server. 3469 Note that there is little point in setting this 3470 value higher than the max_tcp_slot_table_limit. 3471 3472 nfs.nfs4_disable_idmapping= 3473 [NFSv4] When set to the default of '1', this option 3474 ensures that both the RPC level authentication 3475 scheme and the NFS level operations agree to use 3476 numeric uids/gids if the mount is using the 3477 'sec=sys' security flavour. In effect it is 3478 disabling idmapping, which can make migration from 3479 legacy NFSv2/v3 systems to NFSv4 easier. 3480 Servers that do not support this mode of operation 3481 will be autodetected by the client, and it will fall 3482 back to using the idmapper. 3483 To turn off this behaviour, set the value to '0'. 3484 nfs.nfs4_unique_id= 3485 [NFS4] Specify an additional fixed unique ident- 3486 ification string that NFSv4 clients can insert into 3487 their nfs_client_id4 string. This is typically a 3488 UUID that is generated at system install time. 3489 3490 nfs.send_implementation_id = 3491 [NFSv4.1] Send client implementation identification 3492 information in exchange_id requests. 3493 If zero, no implementation identification information 3494 will be sent. 3495 The default is to send the implementation identification 3496 information. 3497 3498 nfs.recover_lost_locks = 3499 [NFSv4] Attempt to recover locks that were lost due 3500 to a lease timeout on the server. Please note that 3501 doing this risks data corruption, since there are 3502 no guarantees that the file will remain unchanged 3503 after the locks are lost. 3504 If you want to enable the kernel legacy behaviour of 3505 attempting to recover these locks, then set this 3506 parameter to '1'. 3507 The default parameter value of '0' causes the kernel 3508 not to attempt recovery of lost locks. 3509 3510 nfs4.layoutstats_timer = 3511 [NFSv4.2] Change the rate at which the kernel sends 3512 layoutstats to the pNFS metadata server. 3513 3514 Setting this to value to 0 causes the kernel to use 3515 whatever value is the default set by the layout 3516 driver. A non-zero value sets the minimum interval 3517 in seconds between layoutstats transmissions. 3518 3519 nfsd.inter_copy_offload_enable = 3520 [NFSv4.2] When set to 1, the server will support 3521 server-to-server copies for which this server is 3522 the destination of the copy. 3523 3524 nfsd.nfsd4_ssc_umount_timeout = 3525 [NFSv4.2] When used as the destination of a 3526 server-to-server copy, knfsd temporarily mounts 3527 the source server. It caches the mount in case 3528 it will be needed again, and discards it if not 3529 used for the number of milliseconds specified by 3530 this parameter. 3531 3532 nfsd.nfs4_disable_idmapping= 3533 [NFSv4] When set to the default of '1', the NFSv4 3534 server will return only numeric uids and gids to 3535 clients using auth_sys, and will accept numeric uids 3536 and gids from such clients. This is intended to ease 3537 migration from NFSv2/v3. 3538 3539 3540 nmi_backtrace.backtrace_idle [KNL] 3541 Dump stacks even of idle CPUs in response to an 3542 NMI stack-backtrace request. 3543 3544 nmi_debug= [KNL,SH] Specify one or more actions to take 3545 when a NMI is triggered. 3546 Format: [state][,regs][,debounce][,die] 3547 3548 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3549 Format: [panic,][nopanic,][num] 3550 Valid num: 0 or 1 3551 0 - turn hardlockup detector in nmi_watchdog off 3552 1 - turn hardlockup detector in nmi_watchdog on 3553 When panic is specified, panic when an NMI watchdog 3554 timeout occurs (or 'nopanic' to not panic on an NMI 3555 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3556 To disable both hard and soft lockup detectors, 3557 please see 'nowatchdog'. 3558 This is useful when you use a panic=... timeout and 3559 need the box quickly up again. 3560 3561 These settings can be accessed at runtime via 3562 the nmi_watchdog and hardlockup_panic sysctls. 3563 3564 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3565 emulation library even if a 387 maths coprocessor 3566 is present. 3567 3568 no5lvl [X86-64] Disable 5-level paging mode. Forces 3569 kernel to use 4-level paging instead. 3570 3571 nofsgsbase [X86] Disables FSGSBASE instructions. 3572 3573 no_console_suspend 3574 [HW] Never suspend the console 3575 Disable suspending of consoles during suspend and 3576 hibernate operations. Once disabled, debugging 3577 messages can reach various consoles while the rest 3578 of the system is being put to sleep (ie, while 3579 debugging driver suspend/resume hooks). This may 3580 not work reliably with all consoles, but is known 3581 to work with serial and VGA consoles. 3582 To facilitate more flexible debugging, we also add 3583 console_suspend, a printk module parameter to control 3584 it. Users could use console_suspend (usually 3585 /sys/module/printk/parameters/console_suspend) to 3586 turn on/off it dynamically. 3587 3588 novmcoredd [KNL,KDUMP] 3589 Disable device dump. Device dump allows drivers to 3590 append dump data to vmcore so you can collect driver 3591 specified debug info. Drivers can append the data 3592 without any limit and this data is stored in memory, 3593 so this may cause significant memory stress. Disabling 3594 device dump can help save memory but the driver debug 3595 data will be no longer available. This parameter 3596 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3597 is set. 3598 3599 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3600 caches in the slab allocator. Saves per-node memory, 3601 but will impact performance. 3602 3603 noalign [KNL,ARM] 3604 3605 noaltinstr [S390] Disables alternative instructions patching 3606 (CPU alternatives feature). 3607 3608 noapic [SMP,APIC] Tells the kernel to not make use of any 3609 IOAPICs that may be present in the system. 3610 3611 noautogroup Disable scheduler automatic task group creation. 3612 3613 nocache [ARM] 3614 3615 nodsp [SH] Disable hardware DSP at boot time. 3616 3617 noefi Disable EFI runtime services support. 3618 3619 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3620 3621 noexec [IA-64] 3622 3623 nosmap [PPC] 3624 Disable SMAP (Supervisor Mode Access Prevention) 3625 even if it is supported by processor. 3626 3627 nosmep [PPC64s] 3628 Disable SMEP (Supervisor Mode Execution Prevention) 3629 even if it is supported by processor. 3630 3631 noexec32 [X86-64] 3632 This affects only 32-bit executables. 3633 noexec32=on: enable non-executable mappings (default) 3634 read doesn't imply executable mappings 3635 noexec32=off: disable non-executable mappings 3636 read implies executable mappings 3637 3638 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3639 3640 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3641 register save and restore. The kernel will only save 3642 legacy floating-point registers on task switch. 3643 3644 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3645 3646 nohugevmalloc [KNL,X86,PPC,ARM64] Disable kernel huge vmalloc mappings. 3647 3648 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3649 Equivalent to smt=1. 3650 3651 [KNL,X86] Disable symmetric multithreading (SMT). 3652 nosmt=force: Force disable SMT, cannot be undone 3653 via the sysfs control file. 3654 3655 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3656 (bounds check bypass). With this option data leaks are 3657 possible in the system. 3658 3659 nospectre_v2 [X86,PPC_E500,ARM64] Disable all mitigations for 3660 the Spectre variant 2 (indirect branch prediction) 3661 vulnerability. System may allow data leaks with this 3662 option. 3663 3664 nospectre_bhb [ARM64] Disable all mitigations for Spectre-BHB (branch 3665 history injection) vulnerability. System may allow data leaks 3666 with this option. 3667 3668 nospec_store_bypass_disable 3669 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3670 3671 no_uaccess_flush 3672 [PPC] Don't flush the L1-D cache after accessing user data. 3673 3674 noxsave [BUGS=X86] Disables x86 extended register state save 3675 and restore using xsave. The kernel will fallback to 3676 enabling legacy floating-point and sse state. 3677 3678 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3679 register states. The kernel will fall back to use 3680 xsave to save the states. By using this parameter, 3681 performance of saving the states is degraded because 3682 xsave doesn't support modified optimization while 3683 xsaveopt supports it on xsaveopt enabled systems. 3684 3685 noxsaves [X86] Disables xsaves and xrstors used in saving and 3686 restoring x86 extended register state in compacted 3687 form of xsave area. The kernel will fall back to use 3688 xsaveopt and xrstor to save and restore the states 3689 in standard form of xsave area. By using this 3690 parameter, xsave area per process might occupy more 3691 memory on xsaves enabled systems. 3692 3693 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait 3694 in do_idle() and not use the arch_cpu_idle() 3695 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 3696 to be effective. This is useful on platforms where the 3697 sleep(SH) or wfi(ARM,ARM64) instructions do not work 3698 correctly or when doing power measurements to evalute 3699 the impact of the sleep instructions. This is also 3700 useful when using JTAG debugger. 3701 3702 no_file_caps Tells the kernel not to honor file capabilities. The 3703 only way then for a file to be executed with privilege 3704 is to be setuid root or executed by root. 3705 3706 nohalt [IA-64] Tells the kernel not to use the power saving 3707 function PAL_HALT_LIGHT when idle. This increases 3708 power-consumption. On the positive side, it reduces 3709 interrupt wake-up latency, which may improve performance 3710 in certain environments such as networked servers or 3711 real-time systems. 3712 3713 no_hash_pointers 3714 Force pointers printed to the console or buffers to be 3715 unhashed. By default, when a pointer is printed via %p 3716 format string, that pointer is "hashed", i.e. obscured 3717 by hashing the pointer value. This is a security feature 3718 that hides actual kernel addresses from unprivileged 3719 users, but it also makes debugging the kernel more 3720 difficult since unequal pointers can no longer be 3721 compared. However, if this command-line option is 3722 specified, then all normal pointers will have their true 3723 value printed. This option should only be specified when 3724 debugging the kernel. Please do not use on production 3725 kernels. 3726 3727 nohibernate [HIBERNATION] Disable hibernation and resume. 3728 3729 nohz= [KNL] Boottime enable/disable dynamic ticks 3730 Valid arguments: on, off 3731 Default: on 3732 3733 nohz_full= [KNL,BOOT,SMP,ISOL] 3734 The argument is a cpu list, as described above. 3735 In kernels built with CONFIG_NO_HZ_FULL=y, set 3736 the specified list of CPUs whose tick will be stopped 3737 whenever possible. The boot CPU will be forced outside 3738 the range to maintain the timekeeping. Any CPUs 3739 in this list will have their RCU callbacks offloaded, 3740 just as if they had also been called out in the 3741 rcu_nocbs= boot parameter. 3742 3743 Note that this argument takes precedence over 3744 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 3745 3746 noiotrap [SH] Disables trapped I/O port accesses. 3747 3748 noirqdebug [X86-32] Disables the code which attempts to detect and 3749 disable unhandled interrupt sources. 3750 3751 no_timer_check [X86,APIC] Disables the code which tests for 3752 broken timer IRQ sources. 3753 3754 noisapnp [ISAPNP] Disables ISA PnP code. 3755 3756 noinitrd [RAM] Tells the kernel not to load any configured 3757 initial RAM disk. 3758 3759 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3760 remapping. 3761 [Deprecated - use intremap=off] 3762 3763 nointroute [IA-64] 3764 3765 noinvpcid [X86] Disable the INVPCID cpu feature. 3766 3767 nojitter [IA-64] Disables jitter checking for ITC timers. 3768 3769 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3770 3771 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3772 fault handling. 3773 3774 no-vmw-sched-clock 3775 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3776 clock and use the default one. 3777 3778 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES] Disable paravirtualized 3779 steal time accounting. steal time is computed, but 3780 won't influence scheduler behaviour 3781 3782 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3783 3784 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3785 3786 nomca [IA-64] Disable machine check abort handling 3787 3788 nomce [X86-32] Disable Machine Check Exception 3789 3790 nomfgpt [X86-32] Disable Multi-Function General Purpose 3791 Timer usage (for AMD Geode machines). 3792 3793 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3794 shutdown the other cpus. Instead use the REBOOT_VECTOR 3795 irq. 3796 3797 nomodeset Disable kernel modesetting. DRM drivers will not perform 3798 display-mode changes or accelerated rendering. Only the 3799 system framebuffer will be available for use if this was 3800 set-up by the firmware or boot loader. 3801 3802 Useful as fallback, or for testing and debugging. 3803 3804 nomodule Disable module load 3805 3806 nopat [X86] Disable PAT (page attribute table extension of 3807 pagetables) support. 3808 3809 nopcid [X86-64] Disable the PCID cpu feature. 3810 3811 norandmaps Don't use address space randomization. Equivalent to 3812 echo 0 > /proc/sys/kernel/randomize_va_space 3813 3814 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3815 with UP alternatives 3816 3817 noresume [SWSUSP] Disables resume and restores original swap 3818 space. 3819 3820 no-scroll [VGA] Disables scrollback. 3821 This is required for the Braillex ib80-piezo Braille 3822 reader made by F.H. Papenmeier (Germany). 3823 3824 nosbagart [IA-64] 3825 3826 nosgx [X86-64,SGX] Disables Intel SGX kernel support. 3827 3828 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3829 and disable the IO APIC. legacy for "maxcpus=0". 3830 3831 nosoftlockup [KNL] Disable the soft-lockup detector. 3832 3833 nosync [HW,M68K] Disables sync negotiation for all devices. 3834 3835 nowatchdog [KNL] Disable both lockup detectors, i.e. 3836 soft-lockup and NMI watchdog (hard-lockup). 3837 3838 nowb [ARM] 3839 3840 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3841 3842 NOTE: this parameter will be ignored on systems with the 3843 LEGACY_XAPIC_DISABLED bit set in the 3844 IA32_XAPIC_DISABLE_STATUS MSR. 3845 3846 nps_mtm_hs_ctr= [KNL,ARC] 3847 This parameter sets the maximum duration, in 3848 cycles, each HW thread of the CTOP can run 3849 without interruptions, before HW switches it. 3850 The actual maximum duration is 16 times this 3851 parameter's value. 3852 Format: integer between 1 and 255 3853 Default: 255 3854 3855 nptcg= [IA-64] Override max number of concurrent global TLB 3856 purges which is reported from either PAL_VM_SUMMARY or 3857 SAL PALO. 3858 3859 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3860 could support. nr_cpus=n : n >= 1 limits the kernel to 3861 support 'n' processors. It could be larger than the 3862 number of already plugged CPU during bootup, later in 3863 runtime you can physically add extra cpu until it reaches 3864 n. So during boot up some boot time memory for per-cpu 3865 variables need be pre-allocated for later physical cpu 3866 hot plugging. 3867 3868 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3869 3870 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only 3871 set up a single NUMA node spanning all memory. 3872 3873 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 3874 NUMA balancing. 3875 Allowed values are enable and disable 3876 3877 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3878 'node', 'default' can be specified 3879 This can be set from sysctl after boot. 3880 See Documentation/admin-guide/sysctl/vm.rst for details. 3881 3882 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3883 See Documentation/core-api/debugging-via-ohci1394.rst for more 3884 info. 3885 3886 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3887 Rather than timing out after 20 ms if an EC 3888 command is not properly ACKed, override the length 3889 of the timeout. We have interrupts disabled while 3890 waiting for the ACK, so if this is set too high 3891 interrupts *may* be lost! 3892 3893 omap_mux= [OMAP] Override bootloader pin multiplexing. 3894 Format: <mux_mode0.mode_name=value>... 3895 For example, to override I2C bus2: 3896 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3897 3898 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 3899 3900 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 3901 3902 boundary - index of last SLC block on Flex-OneNAND. 3903 The remaining blocks are configured as MLC blocks. 3904 lock - Configure if Flex-OneNAND boundary should be locked. 3905 Once locked, the boundary cannot be changed. 3906 1 indicates lock status, 0 indicates unlock status. 3907 3908 oops=panic Always panic on oopses. Default is to just kill the 3909 process, but there is a small probability of 3910 deadlocking the machine. 3911 This will also cause panics on machine check exceptions. 3912 Useful together with panic=30 to trigger a reboot. 3913 3914 page_alloc.shuffle= 3915 [KNL] Boolean flag to control whether the page allocator 3916 should randomize its free lists. The randomization may 3917 be automatically enabled if the kernel detects it is 3918 running on a platform with a direct-mapped memory-side 3919 cache, and this parameter can be used to 3920 override/disable that behavior. The state of the flag 3921 can be read from sysfs at: 3922 /sys/module/page_alloc/parameters/shuffle. 3923 3924 page_owner= [KNL] Boot-time page_owner enabling option. 3925 Storage of the information about who allocated 3926 each page is disabled in default. With this switch, 3927 we can turn it on. 3928 on: enable the feature 3929 3930 page_poison= [KNL] Boot-time parameter changing the state of 3931 poisoning on the buddy allocator, available with 3932 CONFIG_PAGE_POISONING=y. 3933 off: turn off poisoning (default) 3934 on: turn on poisoning 3935 3936 page_reporting.page_reporting_order= 3937 [KNL] Minimal page reporting order 3938 Format: <integer> 3939 Adjust the minimal page reporting order. The page 3940 reporting is disabled when it exceeds (MAX_ORDER-1). 3941 3942 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3943 timeout > 0: seconds before rebooting 3944 timeout = 0: wait forever 3945 timeout < 0: reboot immediately 3946 Format: <timeout> 3947 3948 panic_print= Bitmask for printing system info when panic happens. 3949 User can chose combination of the following bits: 3950 bit 0: print all tasks info 3951 bit 1: print system memory info 3952 bit 2: print timer info 3953 bit 3: print locks info if CONFIG_LOCKDEP is on 3954 bit 4: print ftrace buffer 3955 bit 5: print all printk messages in buffer 3956 bit 6: print all CPUs backtrace (if available in the arch) 3957 *Be aware* that this option may print a _lot_ of lines, 3958 so there are risks of losing older messages in the log. 3959 Use this option carefully, maybe worth to setup a 3960 bigger log buffer with "log_buf_len" along with this. 3961 3962 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3963 Format: <hex>[,nousertaint] 3964 Hexadecimal bitmask representing the set of TAINT flags 3965 that will cause the kernel to panic when add_taint() is 3966 called with any of the flags in this set. 3967 The optional switch "nousertaint" can be utilized to 3968 prevent userspace forced crashes by writing to sysctl 3969 /proc/sys/kernel/tainted any flagset matching with the 3970 bitmask set on panic_on_taint. 3971 See Documentation/admin-guide/tainted-kernels.rst for 3972 extra details on the taint flags that users can pick 3973 to compose the bitmask to assign to panic_on_taint. 3974 3975 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3976 on a WARN(). 3977 3978 parkbd.port= [HW] Parallel port number the keyboard adapter is 3979 connected to, default is 0. 3980 Format: <parport#> 3981 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3982 0 for XT, 1 for AT (default is AT). 3983 Format: <mode> 3984 3985 parport= [HW,PPT] Specify parallel ports. 0 disables. 3986 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3987 Use 'auto' to force the driver to use any 3988 IRQ/DMA settings detected (the default is to 3989 ignore detected IRQ/DMA settings because of 3990 possible conflicts). You can specify the base 3991 address, IRQ, and DMA settings; IRQ and DMA 3992 should be numbers, or 'auto' (for using detected 3993 settings on that particular port), or 'nofifo' 3994 (to avoid using a FIFO even if it is detected). 3995 Parallel ports are assigned in the order they 3996 are specified on the command line, starting 3997 with parport0. 3998 3999 parport_init_mode= [HW,PPT] 4000 Configure VIA parallel port to operate in 4001 a specific mode. This is necessary on Pegasos 4002 computer where firmware has no options for setting 4003 up parallel port mode and sets it to spp. 4004 Currently this function knows 686a and 8231 chips. 4005 Format: [spp|ps2|epp|ecp|ecpepp] 4006 4007 pata_legacy.all= [HW,LIBATA] 4008 Format: <int> 4009 Set to non-zero to probe primary and secondary ISA 4010 port ranges on PCI systems where no PCI PATA device 4011 has been found at either range. Disabled by default. 4012 4013 pata_legacy.autospeed= [HW,LIBATA] 4014 Format: <int> 4015 Set to non-zero if a chip is present that snoops speed 4016 changes. Disabled by default. 4017 4018 pata_legacy.ht6560a= [HW,LIBATA] 4019 Format: <int> 4020 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4021 the secondary channel, or both channels respectively. 4022 Disabled by default. 4023 4024 pata_legacy.ht6560b= [HW,LIBATA] 4025 Format: <int> 4026 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4027 the secondary channel, or both channels respectively. 4028 Disabled by default. 4029 4030 pata_legacy.iordy_mask= [HW,LIBATA] 4031 Format: <int> 4032 IORDY enable mask. Set individual bits to allow IORDY 4033 for the respective channel. Bit 0 is for the first 4034 legacy channel handled by this driver, bit 1 is for 4035 the second channel, and so on. The sequence will often 4036 correspond to the primary legacy channel, the secondary 4037 legacy channel, and so on, but the handling of a PCI 4038 bus and the use of other driver options may interfere 4039 with the sequence. By default IORDY is allowed across 4040 all channels. 4041 4042 pata_legacy.opti82c46x= [HW,LIBATA] 4043 Format: <int> 4044 Set to 1, 2, or 3 for Opti 82c611A on the primary 4045 channel, the secondary channel, or both channels 4046 respectively. Disabled by default. 4047 4048 pata_legacy.opti82c611a= [HW,LIBATA] 4049 Format: <int> 4050 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4051 channel, the secondary channel, or both channels 4052 respectively. Disabled by default. 4053 4054 pata_legacy.pio_mask= [HW,LIBATA] 4055 Format: <int> 4056 PIO mode mask for autospeed devices. Set individual 4057 bits to allow the use of the respective PIO modes. 4058 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4059 All modes allowed by default. 4060 4061 pata_legacy.probe_all= [HW,LIBATA] 4062 Format: <int> 4063 Set to non-zero to probe tertiary and further ISA 4064 port ranges on PCI systems. Disabled by default. 4065 4066 pata_legacy.probe_mask= [HW,LIBATA] 4067 Format: <int> 4068 Probe mask for legacy ISA PATA ports. Depending on 4069 platform configuration and the use of other driver 4070 options up to 6 legacy ports are supported: 0x1f0, 4071 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 4072 of individual ports can be disabled by setting the 4073 corresponding bits in the mask to 1. Bit 0 is for 4074 the first port in the list above (0x1f0), and so on. 4075 By default all supported ports are probed. 4076 4077 pata_legacy.qdi= [HW,LIBATA] 4078 Format: <int> 4079 Set to non-zero to probe QDI controllers. By default 4080 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 4081 4082 pata_legacy.winbond= [HW,LIBATA] 4083 Format: <int> 4084 Set to non-zero to probe Winbond controllers. Use 4085 the standard I/O port (0x130) if 1, otherwise the 4086 value given is the I/O port to use (typically 0x1b0). 4087 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 4088 0 otherwise. 4089 4090 pata_platform.pio_mask= [HW,LIBATA] 4091 Format: <int> 4092 Supported PIO mode mask. Set individual bits to allow 4093 the use of the respective PIO modes. Bit 0 is for 4094 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 4095 allowed by default. 4096 4097 pause_on_oops= 4098 Halt all CPUs after the first oops has been printed for 4099 the specified number of seconds. This is to be used if 4100 your oopses keep scrolling off the screen. 4101 4102 pcbit= [HW,ISDN] 4103 4104 pcd. [PARIDE] 4105 See header of drivers/block/paride/pcd.c. 4106 See also Documentation/admin-guide/blockdev/paride.rst. 4107 4108 pci=option[,option...] [PCI] various PCI subsystem options. 4109 4110 Some options herein operate on a specific device 4111 or a set of devices (<pci_dev>). These are 4112 specified in one of the following formats: 4113 4114 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 4115 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 4116 4117 Note: the first format specifies a PCI 4118 bus/device/function address which may change 4119 if new hardware is inserted, if motherboard 4120 firmware changes, or due to changes caused 4121 by other kernel parameters. If the 4122 domain is left unspecified, it is 4123 taken to be zero. Optionally, a path 4124 to a device through multiple device/function 4125 addresses can be specified after the base 4126 address (this is more robust against 4127 renumbering issues). The second format 4128 selects devices using IDs from the 4129 configuration space which may match multiple 4130 devices in the system. 4131 4132 earlydump dump PCI config space before the kernel 4133 changes anything 4134 off [X86] don't probe for the PCI bus 4135 bios [X86-32] force use of PCI BIOS, don't access 4136 the hardware directly. Use this if your machine 4137 has a non-standard PCI host bridge. 4138 nobios [X86-32] disallow use of PCI BIOS, only direct 4139 hardware access methods are allowed. Use this 4140 if you experience crashes upon bootup and you 4141 suspect they are caused by the BIOS. 4142 conf1 [X86] Force use of PCI Configuration Access 4143 Mechanism 1 (config address in IO port 0xCF8, 4144 data in IO port 0xCFC, both 32-bit). 4145 conf2 [X86] Force use of PCI Configuration Access 4146 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 4147 the function, IO port 0xCFA, also 8-bit, sets 4148 bus number. The config space is then accessed 4149 through ports 0xC000-0xCFFF). 4150 See http://wiki.osdev.org/PCI for more info 4151 on the configuration access mechanisms. 4152 noaer [PCIE] If the PCIEAER kernel config parameter is 4153 enabled, this kernel boot option can be used to 4154 disable the use of PCIE advanced error reporting. 4155 nodomains [PCI] Disable support for multiple PCI 4156 root domains (aka PCI segments, in ACPI-speak). 4157 nommconf [X86] Disable use of MMCONFIG for PCI 4158 Configuration 4159 check_enable_amd_mmconf [X86] check for and enable 4160 properly configured MMIO access to PCI 4161 config space on AMD family 10h CPU 4162 nomsi [MSI] If the PCI_MSI kernel config parameter is 4163 enabled, this kernel boot option can be used to 4164 disable the use of MSI interrupts system-wide. 4165 noioapicquirk [APIC] Disable all boot interrupt quirks. 4166 Safety option to keep boot IRQs enabled. This 4167 should never be necessary. 4168 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 4169 primary IO-APIC for bridges that cannot disable 4170 boot IRQs. This fixes a source of spurious IRQs 4171 when the system masks IRQs. 4172 noioapicreroute [APIC] Disable workaround that uses the 4173 boot IRQ equivalent of an IRQ that connects to 4174 a chipset where boot IRQs cannot be disabled. 4175 The opposite of ioapicreroute. 4176 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 4177 routing table. These calls are known to be buggy 4178 on several machines and they hang the machine 4179 when used, but on other computers it's the only 4180 way to get the interrupt routing table. Try 4181 this option if the kernel is unable to allocate 4182 IRQs or discover secondary PCI buses on your 4183 motherboard. 4184 rom [X86] Assign address space to expansion ROMs. 4185 Use with caution as certain devices share 4186 address decoders between ROMs and other 4187 resources. 4188 norom [X86] Do not assign address space to 4189 expansion ROMs that do not already have 4190 BIOS assigned address ranges. 4191 nobar [X86] Do not assign address space to the 4192 BARs that weren't assigned by the BIOS. 4193 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 4194 assigned automatically to PCI devices. You can 4195 make the kernel exclude IRQs of your ISA cards 4196 this way. 4197 pirqaddr=0xAAAAA [X86] Specify the physical address 4198 of the PIRQ table (normally generated 4199 by the BIOS) if it is outside the 4200 F0000h-100000h range. 4201 lastbus=N [X86] Scan all buses thru bus #N. Can be 4202 useful if the kernel is unable to find your 4203 secondary buses and you want to tell it 4204 explicitly which ones they are. 4205 assign-busses [X86] Always assign all PCI bus 4206 numbers ourselves, overriding 4207 whatever the firmware may have done. 4208 usepirqmask [X86] Honor the possible IRQ mask stored 4209 in the BIOS $PIR table. This is needed on 4210 some systems with broken BIOSes, notably 4211 some HP Pavilion N5400 and Omnibook XE3 4212 notebooks. This will have no effect if ACPI 4213 IRQ routing is enabled. 4214 noacpi [X86] Do not use ACPI for IRQ routing 4215 or for PCI scanning. 4216 use_crs [X86] Use PCI host bridge window information 4217 from ACPI. On BIOSes from 2008 or later, this 4218 is enabled by default. If you need to use this, 4219 please report a bug. 4220 nocrs [X86] Ignore PCI host bridge windows from ACPI. 4221 If you need to use this, please report a bug. 4222 use_e820 [X86] Use E820 reservations to exclude parts of 4223 PCI host bridge windows. This is a workaround 4224 for BIOS defects in host bridge _CRS methods. 4225 If you need to use this, please report a bug to 4226 <linux-pci@vger.kernel.org>. 4227 no_e820 [X86] Ignore E820 reservations for PCI host 4228 bridge windows. This is the default on modern 4229 hardware. If you need to use this, please report 4230 a bug to <linux-pci@vger.kernel.org>. 4231 routeirq Do IRQ routing for all PCI devices. 4232 This is normally done in pci_enable_device(), 4233 so this option is a temporary workaround 4234 for broken drivers that don't call it. 4235 skip_isa_align [X86] do not align io start addr, so can 4236 handle more pci cards 4237 noearly [X86] Don't do any early type 1 scanning. 4238 This might help on some broken boards which 4239 machine check when some devices' config space 4240 is read. But various workarounds are disabled 4241 and some IOMMU drivers will not work. 4242 bfsort Sort PCI devices into breadth-first order. 4243 This sorting is done to get a device 4244 order compatible with older (<= 2.4) kernels. 4245 nobfsort Don't sort PCI devices into breadth-first order. 4246 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 4247 tuning and use the BIOS-configured MPS defaults. 4248 pcie_bus_safe Set every device's MPS to the largest value 4249 supported by all devices below the root complex. 4250 pcie_bus_perf Set device MPS to the largest allowable MPS 4251 based on its parent bus. Also set MRRS (Max 4252 Read Request Size) to the largest supported 4253 value (no larger than the MPS that the device 4254 or bus can support) for best performance. 4255 pcie_bus_peer2peer Set every device's MPS to 128B, which 4256 every device is guaranteed to support. This 4257 configuration allows peer-to-peer DMA between 4258 any pair of devices, possibly at the cost of 4259 reduced performance. This also guarantees 4260 that hot-added devices will work. 4261 cbiosize=nn[KMG] The fixed amount of bus space which is 4262 reserved for the CardBus bridge's IO window. 4263 The default value is 256 bytes. 4264 cbmemsize=nn[KMG] The fixed amount of bus space which is 4265 reserved for the CardBus bridge's memory 4266 window. The default value is 64 megabytes. 4267 resource_alignment= 4268 Format: 4269 [<order of align>@]<pci_dev>[; ...] 4270 Specifies alignment and device to reassign 4271 aligned memory resources. How to 4272 specify the device is described above. 4273 If <order of align> is not specified, 4274 PAGE_SIZE is used as alignment. 4275 A PCI-PCI bridge can be specified if resource 4276 windows need to be expanded. 4277 To specify the alignment for several 4278 instances of a device, the PCI vendor, 4279 device, subvendor, and subdevice may be 4280 specified, e.g., 12@pci:8086:9c22:103c:198f 4281 for 4096-byte alignment. 4282 ecrc= Enable/disable PCIe ECRC (transaction layer 4283 end-to-end CRC checking). 4284 bios: Use BIOS/firmware settings. This is the 4285 the default. 4286 off: Turn ECRC off 4287 on: Turn ECRC on. 4288 hpiosize=nn[KMG] The fixed amount of bus space which is 4289 reserved for hotplug bridge's IO window. 4290 Default size is 256 bytes. 4291 hpmmiosize=nn[KMG] The fixed amount of bus space which is 4292 reserved for hotplug bridge's MMIO window. 4293 Default size is 2 megabytes. 4294 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 4295 reserved for hotplug bridge's MMIO_PREF window. 4296 Default size is 2 megabytes. 4297 hpmemsize=nn[KMG] The fixed amount of bus space which is 4298 reserved for hotplug bridge's MMIO and 4299 MMIO_PREF window. 4300 Default size is 2 megabytes. 4301 hpbussize=nn The minimum amount of additional bus numbers 4302 reserved for buses below a hotplug bridge. 4303 Default is 1. 4304 realloc= Enable/disable reallocating PCI bridge resources 4305 if allocations done by BIOS are too small to 4306 accommodate resources required by all child 4307 devices. 4308 off: Turn realloc off 4309 on: Turn realloc on 4310 realloc same as realloc=on 4311 noari do not use PCIe ARI. 4312 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 4313 do not use PCIe ATS (and IOMMU device IOTLB). 4314 pcie_scan_all Scan all possible PCIe devices. Otherwise we 4315 only look for one device below a PCIe downstream 4316 port. 4317 big_root_window Try to add a big 64bit memory window to the PCIe 4318 root complex on AMD CPUs. Some GFX hardware 4319 can resize a BAR to allow access to all VRAM. 4320 Adding the window is slightly risky (it may 4321 conflict with unreported devices), so this 4322 taints the kernel. 4323 disable_acs_redir=<pci_dev>[; ...] 4324 Specify one or more PCI devices (in the format 4325 specified above) separated by semicolons. 4326 Each device specified will have the PCI ACS 4327 redirect capabilities forced off which will 4328 allow P2P traffic between devices through 4329 bridges without forcing it upstream. Note: 4330 this removes isolation between devices and 4331 may put more devices in an IOMMU group. 4332 force_floating [S390] Force usage of floating interrupts. 4333 nomio [S390] Do not use MIO instructions. 4334 norid [S390] ignore the RID field and force use of 4335 one PCI domain per PCI function 4336 4337 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 4338 Management. 4339 off Disable ASPM. 4340 force Enable ASPM even on devices that claim not to support it. 4341 WARNING: Forcing ASPM on may cause system lockups. 4342 4343 pcie_ports= [PCIE] PCIe port services handling: 4344 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 4345 even if the platform doesn't give the OS permission to 4346 use them. This may cause conflicts if the platform 4347 also tries to use these services. 4348 dpc-native Use native PCIe service for DPC only. May 4349 cause conflicts if firmware uses AER or DPC. 4350 compat Disable native PCIe services (PME, AER, DPC, PCIe 4351 hotplug). 4352 4353 pcie_port_pm= [PCIE] PCIe port power management handling: 4354 off Disable power management of all PCIe ports 4355 force Forcibly enable power management of all PCIe ports 4356 4357 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 4358 nomsi Do not use MSI for native PCIe PME signaling (this makes 4359 all PCIe root ports use INTx for all services). 4360 4361 pcmv= [HW,PCMCIA] BadgePAD 4 4362 4363 pd_ignore_unused 4364 [PM] 4365 Keep all power-domains already enabled by bootloader on, 4366 even if no driver has claimed them. This is useful 4367 for debug and development, but should not be 4368 needed on a platform with proper driver support. 4369 4370 pd. [PARIDE] 4371 See Documentation/admin-guide/blockdev/paride.rst. 4372 4373 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 4374 boot time. 4375 Format: { 0 | 1 } 4376 See arch/parisc/kernel/pdc_chassis.c 4377 4378 percpu_alloc= Select which percpu first chunk allocator to use. 4379 Currently supported values are "embed" and "page". 4380 Archs may support subset or none of the selections. 4381 See comments in mm/percpu.c for details on each 4382 allocator. This parameter is primarily for debugging 4383 and performance comparison. 4384 4385 pf. [PARIDE] 4386 See Documentation/admin-guide/blockdev/paride.rst. 4387 4388 pg. [PARIDE] 4389 See Documentation/admin-guide/blockdev/paride.rst. 4390 4391 pirq= [SMP,APIC] Manual mp-table setup 4392 See Documentation/x86/i386/IO-APIC.rst. 4393 4394 plip= [PPT,NET] Parallel port network link 4395 Format: { parport<nr> | timid | 0 } 4396 See also Documentation/admin-guide/parport.rst. 4397 4398 pmtmr= [X86] Manual setup of pmtmr I/O Port. 4399 Override pmtimer IOPort with a hex value. 4400 e.g. pmtmr=0x508 4401 4402 pmu_override= [PPC] Override the PMU. 4403 This option takes over the PMU facility, so it is no 4404 longer usable by perf. Setting this option starts the 4405 PMU counters by setting MMCR0 to 0 (the FC bit is 4406 cleared). If a number is given, then MMCR1 is set to 4407 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 4408 remains 0. 4409 4410 pm_debug_messages [SUSPEND,KNL] 4411 Enable suspend/resume debug messages during boot up. 4412 4413 pnp.debug=1 [PNP] 4414 Enable PNP debug messages (depends on the 4415 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 4416 via /sys/module/pnp/parameters/debug. We always show 4417 current resource usage; turning this on also shows 4418 possible settings and some assignment information. 4419 4420 pnpacpi= [ACPI] 4421 { off } 4422 4423 pnpbios= [ISAPNP] 4424 { on | off | curr | res | no-curr | no-res } 4425 4426 pnp_reserve_irq= 4427 [ISAPNP] Exclude IRQs for the autoconfiguration 4428 4429 pnp_reserve_dma= 4430 [ISAPNP] Exclude DMAs for the autoconfiguration 4431 4432 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 4433 Ranges are in pairs (I/O port base and size). 4434 4435 pnp_reserve_mem= 4436 [ISAPNP] Exclude memory regions for the 4437 autoconfiguration. 4438 Ranges are in pairs (memory base and size). 4439 4440 ports= [IP_VS_FTP] IPVS ftp helper module 4441 Default is 21. 4442 Up to 8 (IP_VS_APP_MAX_PORTS) ports 4443 may be specified. 4444 Format: <port>,<port>.... 4445 4446 powersave=off [PPC] This option disables power saving features. 4447 It specifically disables cpuidle and sets the 4448 platform machine description specific power_save 4449 function to NULL. On Idle the CPU just reduces 4450 execution priority. 4451 4452 ppc_strict_facility_enable 4453 [PPC] This option catches any kernel floating point, 4454 Altivec, VSX and SPE outside of regions specifically 4455 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 4456 There is some performance impact when enabling this. 4457 4458 ppc_tm= [PPC] 4459 Format: {"off"} 4460 Disable Hardware Transactional Memory 4461 4462 preempt= [KNL] 4463 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 4464 none - Limited to cond_resched() calls 4465 voluntary - Limited to cond_resched() and might_sleep() calls 4466 full - Any section that isn't explicitly preempt disabled 4467 can be preempted anytime. 4468 4469 print-fatal-signals= 4470 [KNL] debug: print fatal signals 4471 4472 If enabled, warn about various signal handling 4473 related application anomalies: too many signals, 4474 too many POSIX.1 timers, fatal signals causing a 4475 coredump - etc. 4476 4477 If you hit the warning due to signal overflow, 4478 you might want to try "ulimit -i unlimited". 4479 4480 default: off. 4481 4482 printk.always_kmsg_dump= 4483 Trigger kmsg_dump for cases other than kernel oops or 4484 panics 4485 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4486 default: disabled 4487 4488 printk.console_no_auto_verbose= 4489 Disable console loglevel raise on oops, panic 4490 or lockdep-detected issues (only if lock debug is on). 4491 With an exception to setups with low baudrate on 4492 serial console, keeping this 0 is a good choice 4493 in order to provide more debug information. 4494 Format: <bool> 4495 default: 0 (auto_verbose is enabled) 4496 4497 printk.devkmsg={on,off,ratelimit} 4498 Control writing to /dev/kmsg. 4499 on - unlimited logging to /dev/kmsg from userspace 4500 off - logging to /dev/kmsg disabled 4501 ratelimit - ratelimit the logging 4502 Default: ratelimit 4503 4504 printk.time= Show timing data prefixed to each printk message line 4505 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4506 4507 processor.max_cstate= [HW,ACPI] 4508 Limit processor to maximum C-state 4509 max_cstate=9 overrides any DMI blacklist limit. 4510 4511 processor.nocst [HW,ACPI] 4512 Ignore the _CST method to determine C-states, 4513 instead using the legacy FADT method 4514 4515 profile= [KNL] Enable kernel profiling via /proc/profile 4516 Format: [<profiletype>,]<number> 4517 Param: <profiletype>: "schedule", "sleep", or "kvm" 4518 [defaults to kernel profiling] 4519 Param: "schedule" - profile schedule points. 4520 Param: "sleep" - profile D-state sleeping (millisecs). 4521 Requires CONFIG_SCHEDSTATS 4522 Param: "kvm" - profile VM exits. 4523 Param: <number> - step/bucket size as a power of 2 for 4524 statistical time based profiling. 4525 4526 prompt_ramdisk= [RAM] [Deprecated] 4527 4528 prot_virt= [S390] enable hosting protected virtual machines 4529 isolated from the hypervisor (if hardware supports 4530 that). 4531 Format: <bool> 4532 4533 psi= [KNL] Enable or disable pressure stall information 4534 tracking. 4535 Format: <bool> 4536 4537 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 4538 probe for; one of (bare|imps|exps|lifebook|any). 4539 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 4540 per second. 4541 psmouse.resetafter= [HW,MOUSE] 4542 Try to reset the device after so many bad packets 4543 (0 = never). 4544 psmouse.resolution= 4545 [HW,MOUSE] Set desired mouse resolution, in dpi. 4546 psmouse.smartscroll= 4547 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 4548 0 = disabled, 1 = enabled (default). 4549 4550 pstore.backend= Specify the name of the pstore backend to use 4551 4552 pt. [PARIDE] 4553 See Documentation/admin-guide/blockdev/paride.rst. 4554 4555 pti= [X86-64] Control Page Table Isolation of user and 4556 kernel address spaces. Disabling this feature 4557 removes hardening, but improves performance of 4558 system calls and interrupts. 4559 4560 on - unconditionally enable 4561 off - unconditionally disable 4562 auto - kernel detects whether your CPU model is 4563 vulnerable to issues that PTI mitigates 4564 4565 Not specifying this option is equivalent to pti=auto. 4566 4567 nopti [X86-64] 4568 Equivalent to pti=off 4569 4570 pty.legacy_count= 4571 [KNL] Number of legacy pty's. Overwrites compiled-in 4572 default number. 4573 4574 quiet [KNL] Disable most log messages 4575 4576 r128= [HW,DRM] 4577 4578 raid= [HW,RAID] 4579 See Documentation/admin-guide/md.rst. 4580 4581 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4582 See Documentation/admin-guide/blockdev/ramdisk.rst. 4583 4584 ramdisk_start= [RAM] RAM disk image start address 4585 4586 random.trust_cpu={on,off} 4587 [KNL] Enable or disable trusting the use of the 4588 CPU's random number generator (if available) to 4589 fully seed the kernel's CRNG. Default is controlled 4590 by CONFIG_RANDOM_TRUST_CPU. 4591 4592 random.trust_bootloader={on,off} 4593 [KNL] Enable or disable trusting the use of a 4594 seed passed by the bootloader (if available) to 4595 fully seed the kernel's CRNG. Default is controlled 4596 by CONFIG_RANDOM_TRUST_BOOTLOADER. 4597 4598 randomize_kstack_offset= 4599 [KNL] Enable or disable kernel stack offset 4600 randomization, which provides roughly 5 bits of 4601 entropy, frustrating memory corruption attacks 4602 that depend on stack address determinism or 4603 cross-syscall address exposures. This is only 4604 available on architectures that have defined 4605 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 4606 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4607 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 4608 4609 ras=option[,option,...] [KNL] RAS-specific options 4610 4611 cec_disable [X86] 4612 Disable the Correctable Errors Collector, 4613 see CONFIG_RAS_CEC help text. 4614 4615 rcu_nocbs[=cpu-list] 4616 [KNL] The optional argument is a cpu list, 4617 as described above. 4618 4619 In kernels built with CONFIG_RCU_NOCB_CPU=y, 4620 enable the no-callback CPU mode, which prevents 4621 such CPUs' callbacks from being invoked in 4622 softirq context. Invocation of such CPUs' RCU 4623 callbacks will instead be offloaded to "rcuox/N" 4624 kthreads created for that purpose, where "x" is 4625 "p" for RCU-preempt, "s" for RCU-sched, and "g" 4626 for the kthreads that mediate grace periods; and 4627 "N" is the CPU number. This reduces OS jitter on 4628 the offloaded CPUs, which can be useful for HPC 4629 and real-time workloads. It can also improve 4630 energy efficiency for asymmetric multiprocessors. 4631 4632 If a cpulist is passed as an argument, the specified 4633 list of CPUs is set to no-callback mode from boot. 4634 4635 Otherwise, if the '=' sign and the cpulist 4636 arguments are omitted, no CPU will be set to 4637 no-callback mode from boot but the mode may be 4638 toggled at runtime via cpusets. 4639 4640 Note that this argument takes precedence over 4641 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4642 4643 rcu_nocb_poll [KNL] 4644 Rather than requiring that offloaded CPUs 4645 (specified by rcu_nocbs= above) explicitly 4646 awaken the corresponding "rcuoN" kthreads, 4647 make these kthreads poll for callbacks. 4648 This improves the real-time response for the 4649 offloaded CPUs by relieving them of the need to 4650 wake up the corresponding kthread, but degrades 4651 energy efficiency by requiring that the kthreads 4652 periodically wake up to do the polling. 4653 4654 rcutree.blimit= [KNL] 4655 Set maximum number of finished RCU callbacks to 4656 process in one batch. 4657 4658 rcutree.dump_tree= [KNL] 4659 Dump the structure of the rcu_node combining tree 4660 out at early boot. This is used for diagnostic 4661 purposes, to verify correct tree setup. 4662 4663 rcutree.gp_cleanup_delay= [KNL] 4664 Set the number of jiffies to delay each step of 4665 RCU grace-period cleanup. 4666 4667 rcutree.gp_init_delay= [KNL] 4668 Set the number of jiffies to delay each step of 4669 RCU grace-period initialization. 4670 4671 rcutree.gp_preinit_delay= [KNL] 4672 Set the number of jiffies to delay each step of 4673 RCU grace-period pre-initialization, that is, 4674 the propagation of recent CPU-hotplug changes up 4675 the rcu_node combining tree. 4676 4677 rcutree.use_softirq= [KNL] 4678 If set to zero, move all RCU_SOFTIRQ processing to 4679 per-CPU rcuc kthreads. Defaults to a non-zero 4680 value, meaning that RCU_SOFTIRQ is used by default. 4681 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4682 4683 But note that CONFIG_PREEMPT_RT=y kernels disable 4684 this kernel boot parameter, forcibly setting it 4685 to zero. 4686 4687 rcutree.rcu_fanout_exact= [KNL] 4688 Disable autobalancing of the rcu_node combining 4689 tree. This is used by rcutorture, and might 4690 possibly be useful for architectures having high 4691 cache-to-cache transfer latencies. 4692 4693 rcutree.rcu_fanout_leaf= [KNL] 4694 Change the number of CPUs assigned to each 4695 leaf rcu_node structure. Useful for very 4696 large systems, which will choose the value 64, 4697 and for NUMA systems with large remote-access 4698 latencies, which will choose a value aligned 4699 with the appropriate hardware boundaries. 4700 4701 rcutree.rcu_min_cached_objs= [KNL] 4702 Minimum number of objects which are cached and 4703 maintained per one CPU. Object size is equal 4704 to PAGE_SIZE. The cache allows to reduce the 4705 pressure to page allocator, also it makes the 4706 whole algorithm to behave better in low memory 4707 condition. 4708 4709 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 4710 Set the page-cache refill delay (in milliseconds) 4711 in response to low-memory conditions. The range 4712 of permitted values is in the range 0:100000. 4713 4714 rcutree.jiffies_till_first_fqs= [KNL] 4715 Set delay from grace-period initialization to 4716 first attempt to force quiescent states. 4717 Units are jiffies, minimum value is zero, 4718 and maximum value is HZ. 4719 4720 rcutree.jiffies_till_next_fqs= [KNL] 4721 Set delay between subsequent attempts to force 4722 quiescent states. Units are jiffies, minimum 4723 value is one, and maximum value is HZ. 4724 4725 rcutree.jiffies_till_sched_qs= [KNL] 4726 Set required age in jiffies for a 4727 given grace period before RCU starts 4728 soliciting quiescent-state help from 4729 rcu_note_context_switch() and cond_resched(). 4730 If not specified, the kernel will calculate 4731 a value based on the most recent settings 4732 of rcutree.jiffies_till_first_fqs 4733 and rcutree.jiffies_till_next_fqs. 4734 This calculated value may be viewed in 4735 rcutree.jiffies_to_sched_qs. Any attempt to set 4736 rcutree.jiffies_to_sched_qs will be cheerfully 4737 overwritten. 4738 4739 rcutree.kthread_prio= [KNL,BOOT] 4740 Set the SCHED_FIFO priority of the RCU per-CPU 4741 kthreads (rcuc/N). This value is also used for 4742 the priority of the RCU boost threads (rcub/N) 4743 and for the RCU grace-period kthreads (rcu_bh, 4744 rcu_preempt, and rcu_sched). If RCU_BOOST is 4745 set, valid values are 1-99 and the default is 1 4746 (the least-favored priority). Otherwise, when 4747 RCU_BOOST is not set, valid values are 0-99 and 4748 the default is zero (non-realtime operation). 4749 When RCU_NOCB_CPU is set, also adjust the 4750 priority of NOCB callback kthreads. 4751 4752 rcutree.rcu_divisor= [KNL] 4753 Set the shift-right count to use to compute 4754 the callback-invocation batch limit bl from 4755 the number of callbacks queued on this CPU. 4756 The result will be bounded below by the value of 4757 the rcutree.blimit kernel parameter. Every bl 4758 callbacks, the softirq handler will exit in 4759 order to allow the CPU to do other work. 4760 4761 Please note that this callback-invocation batch 4762 limit applies only to non-offloaded callback 4763 invocation. Offloaded callbacks are instead 4764 invoked in the context of an rcuoc kthread, which 4765 scheduler will preempt as it does any other task. 4766 4767 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 4768 On callback-offloaded (rcu_nocbs) CPUs, 4769 RCU reduces the lock contention that would 4770 otherwise be caused by callback floods through 4771 use of the ->nocb_bypass list. However, in the 4772 common non-flooded case, RCU queues directly to 4773 the main ->cblist in order to avoid the extra 4774 overhead of the ->nocb_bypass list and its lock. 4775 But if there are too many callbacks queued during 4776 a single jiffy, RCU pre-queues the callbacks into 4777 the ->nocb_bypass queue. The definition of "too 4778 many" is supplied by this kernel boot parameter. 4779 4780 rcutree.rcu_nocb_gp_stride= [KNL] 4781 Set the number of NOCB callback kthreads in 4782 each group, which defaults to the square root 4783 of the number of CPUs. Larger numbers reduce 4784 the wakeup overhead on the global grace-period 4785 kthread, but increases that same overhead on 4786 each group's NOCB grace-period kthread. 4787 4788 rcutree.qhimark= [KNL] 4789 Set threshold of queued RCU callbacks beyond which 4790 batch limiting is disabled. 4791 4792 rcutree.qlowmark= [KNL] 4793 Set threshold of queued RCU callbacks below which 4794 batch limiting is re-enabled. 4795 4796 rcutree.qovld= [KNL] 4797 Set threshold of queued RCU callbacks beyond which 4798 RCU's force-quiescent-state scan will aggressively 4799 enlist help from cond_resched() and sched IPIs to 4800 help CPUs more quickly reach quiescent states. 4801 Set to less than zero to make this be set based 4802 on rcutree.qhimark at boot time and to zero to 4803 disable more aggressive help enlistment. 4804 4805 rcutree.rcu_kick_kthreads= [KNL] 4806 Cause the grace-period kthread to get an extra 4807 wake_up() if it sleeps three times longer than 4808 it should at force-quiescent-state time. 4809 This wake_up() will be accompanied by a 4810 WARN_ONCE() splat and an ftrace_dump(). 4811 4812 rcutree.rcu_unlock_delay= [KNL] 4813 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4814 this specifies an rcu_read_unlock()-time delay 4815 in microseconds. This defaults to zero. 4816 Larger delays increase the probability of 4817 catching RCU pointer leaks, that is, buggy use 4818 of RCU-protected pointers after the relevant 4819 rcu_read_unlock() has completed. 4820 4821 rcutree.sysrq_rcu= [KNL] 4822 Commandeer a sysrq key to dump out Tree RCU's 4823 rcu_node tree with an eye towards determining 4824 why a new grace period has not yet started. 4825 4826 rcuscale.gp_async= [KNL] 4827 Measure performance of asynchronous 4828 grace-period primitives such as call_rcu(). 4829 4830 rcuscale.gp_async_max= [KNL] 4831 Specify the maximum number of outstanding 4832 callbacks per writer thread. When a writer 4833 thread exceeds this limit, it invokes the 4834 corresponding flavor of rcu_barrier() to allow 4835 previously posted callbacks to drain. 4836 4837 rcuscale.gp_exp= [KNL] 4838 Measure performance of expedited synchronous 4839 grace-period primitives. 4840 4841 rcuscale.holdoff= [KNL] 4842 Set test-start holdoff period. The purpose of 4843 this parameter is to delay the start of the 4844 test until boot completes in order to avoid 4845 interference. 4846 4847 rcuscale.kfree_rcu_test= [KNL] 4848 Set to measure performance of kfree_rcu() flooding. 4849 4850 rcuscale.kfree_rcu_test_double= [KNL] 4851 Test the double-argument variant of kfree_rcu(). 4852 If this parameter has the same value as 4853 rcuscale.kfree_rcu_test_single, both the single- 4854 and double-argument variants are tested. 4855 4856 rcuscale.kfree_rcu_test_single= [KNL] 4857 Test the single-argument variant of kfree_rcu(). 4858 If this parameter has the same value as 4859 rcuscale.kfree_rcu_test_double, both the single- 4860 and double-argument variants are tested. 4861 4862 rcuscale.kfree_nthreads= [KNL] 4863 The number of threads running loops of kfree_rcu(). 4864 4865 rcuscale.kfree_alloc_num= [KNL] 4866 Number of allocations and frees done in an iteration. 4867 4868 rcuscale.kfree_loops= [KNL] 4869 Number of loops doing rcuscale.kfree_alloc_num number 4870 of allocations and frees. 4871 4872 rcuscale.nreaders= [KNL] 4873 Set number of RCU readers. The value -1 selects 4874 N, where N is the number of CPUs. A value 4875 "n" less than -1 selects N-n+1, where N is again 4876 the number of CPUs. For example, -2 selects N 4877 (the number of CPUs), -3 selects N+1, and so on. 4878 A value of "n" less than or equal to -N selects 4879 a single reader. 4880 4881 rcuscale.nwriters= [KNL] 4882 Set number of RCU writers. The values operate 4883 the same as for rcuscale.nreaders. 4884 N, where N is the number of CPUs 4885 4886 rcuscale.perf_type= [KNL] 4887 Specify the RCU implementation to test. 4888 4889 rcuscale.shutdown= [KNL] 4890 Shut the system down after performance tests 4891 complete. This is useful for hands-off automated 4892 testing. 4893 4894 rcuscale.verbose= [KNL] 4895 Enable additional printk() statements. 4896 4897 rcuscale.writer_holdoff= [KNL] 4898 Write-side holdoff between grace periods, 4899 in microseconds. The default of zero says 4900 no holdoff. 4901 4902 rcutorture.fqs_duration= [KNL] 4903 Set duration of force_quiescent_state bursts 4904 in microseconds. 4905 4906 rcutorture.fqs_holdoff= [KNL] 4907 Set holdoff time within force_quiescent_state bursts 4908 in microseconds. 4909 4910 rcutorture.fqs_stutter= [KNL] 4911 Set wait time between force_quiescent_state bursts 4912 in seconds. 4913 4914 rcutorture.fwd_progress= [KNL] 4915 Specifies the number of kthreads to be used 4916 for RCU grace-period forward-progress testing 4917 for the types of RCU supporting this notion. 4918 Defaults to 1 kthread, values less than zero or 4919 greater than the number of CPUs cause the number 4920 of CPUs to be used. 4921 4922 rcutorture.fwd_progress_div= [KNL] 4923 Specify the fraction of a CPU-stall-warning 4924 period to do tight-loop forward-progress testing. 4925 4926 rcutorture.fwd_progress_holdoff= [KNL] 4927 Number of seconds to wait between successive 4928 forward-progress tests. 4929 4930 rcutorture.fwd_progress_need_resched= [KNL] 4931 Enclose cond_resched() calls within checks for 4932 need_resched() during tight-loop forward-progress 4933 testing. 4934 4935 rcutorture.gp_cond= [KNL] 4936 Use conditional/asynchronous update-side 4937 primitives, if available. 4938 4939 rcutorture.gp_exp= [KNL] 4940 Use expedited update-side primitives, if available. 4941 4942 rcutorture.gp_normal= [KNL] 4943 Use normal (non-expedited) asynchronous 4944 update-side primitives, if available. 4945 4946 rcutorture.gp_sync= [KNL] 4947 Use normal (non-expedited) synchronous 4948 update-side primitives, if available. If all 4949 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4950 rcutorture.gp_normal=, and rcutorture.gp_sync= 4951 are zero, rcutorture acts as if is interpreted 4952 they are all non-zero. 4953 4954 rcutorture.irqreader= [KNL] 4955 Run RCU readers from irq handlers, or, more 4956 accurately, from a timer handler. Not all RCU 4957 flavors take kindly to this sort of thing. 4958 4959 rcutorture.leakpointer= [KNL] 4960 Leak an RCU-protected pointer out of the reader. 4961 This can of course result in splats, and is 4962 intended to test the ability of things like 4963 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 4964 such leaks. 4965 4966 rcutorture.n_barrier_cbs= [KNL] 4967 Set callbacks/threads for rcu_barrier() testing. 4968 4969 rcutorture.nfakewriters= [KNL] 4970 Set number of concurrent RCU writers. These just 4971 stress RCU, they don't participate in the actual 4972 test, hence the "fake". 4973 4974 rcutorture.nocbs_nthreads= [KNL] 4975 Set number of RCU callback-offload togglers. 4976 Zero (the default) disables toggling. 4977 4978 rcutorture.nocbs_toggle= [KNL] 4979 Set the delay in milliseconds between successive 4980 callback-offload toggling attempts. 4981 4982 rcutorture.nreaders= [KNL] 4983 Set number of RCU readers. The value -1 selects 4984 N-1, where N is the number of CPUs. A value 4985 "n" less than -1 selects N-n-2, where N is again 4986 the number of CPUs. For example, -2 selects N 4987 (the number of CPUs), -3 selects N+1, and so on. 4988 4989 rcutorture.object_debug= [KNL] 4990 Enable debug-object double-call_rcu() testing. 4991 4992 rcutorture.onoff_holdoff= [KNL] 4993 Set time (s) after boot for CPU-hotplug testing. 4994 4995 rcutorture.onoff_interval= [KNL] 4996 Set time (jiffies) between CPU-hotplug operations, 4997 or zero to disable CPU-hotplug testing. 4998 4999 rcutorture.read_exit= [KNL] 5000 Set the number of read-then-exit kthreads used 5001 to test the interaction of RCU updaters and 5002 task-exit processing. 5003 5004 rcutorture.read_exit_burst= [KNL] 5005 The number of times in a given read-then-exit 5006 episode that a set of read-then-exit kthreads 5007 is spawned. 5008 5009 rcutorture.read_exit_delay= [KNL] 5010 The delay, in seconds, between successive 5011 read-then-exit testing episodes. 5012 5013 rcutorture.shuffle_interval= [KNL] 5014 Set task-shuffle interval (s). Shuffling tasks 5015 allows some CPUs to go into dyntick-idle mode 5016 during the rcutorture test. 5017 5018 rcutorture.shutdown_secs= [KNL] 5019 Set time (s) after boot system shutdown. This 5020 is useful for hands-off automated testing. 5021 5022 rcutorture.stall_cpu= [KNL] 5023 Duration of CPU stall (s) to test RCU CPU stall 5024 warnings, zero to disable. 5025 5026 rcutorture.stall_cpu_block= [KNL] 5027 Sleep while stalling if set. This will result 5028 in warnings from preemptible RCU in addition 5029 to any other stall-related activity. 5030 5031 rcutorture.stall_cpu_holdoff= [KNL] 5032 Time to wait (s) after boot before inducing stall. 5033 5034 rcutorture.stall_cpu_irqsoff= [KNL] 5035 Disable interrupts while stalling if set. 5036 5037 rcutorture.stall_gp_kthread= [KNL] 5038 Duration (s) of forced sleep within RCU 5039 grace-period kthread to test RCU CPU stall 5040 warnings, zero to disable. If both stall_cpu 5041 and stall_gp_kthread are specified, the 5042 kthread is starved first, then the CPU. 5043 5044 rcutorture.stat_interval= [KNL] 5045 Time (s) between statistics printk()s. 5046 5047 rcutorture.stutter= [KNL] 5048 Time (s) to stutter testing, for example, specifying 5049 five seconds causes the test to run for five seconds, 5050 wait for five seconds, and so on. This tests RCU's 5051 ability to transition abruptly to and from idle. 5052 5053 rcutorture.test_boost= [KNL] 5054 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 5055 "Maybe" means test if the RCU implementation 5056 under test support RCU priority boosting. 5057 5058 rcutorture.test_boost_duration= [KNL] 5059 Duration (s) of each individual boost test. 5060 5061 rcutorture.test_boost_interval= [KNL] 5062 Interval (s) between each boost test. 5063 5064 rcutorture.test_no_idle_hz= [KNL] 5065 Test RCU's dyntick-idle handling. See also the 5066 rcutorture.shuffle_interval parameter. 5067 5068 rcutorture.torture_type= [KNL] 5069 Specify the RCU implementation to test. 5070 5071 rcutorture.verbose= [KNL] 5072 Enable additional printk() statements. 5073 5074 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 5075 Dump ftrace buffer after reporting RCU CPU 5076 stall warning. 5077 5078 rcupdate.rcu_cpu_stall_suppress= [KNL] 5079 Suppress RCU CPU stall warning messages. 5080 5081 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 5082 Suppress RCU CPU stall warning messages and 5083 rcutorture writer stall warnings that occur 5084 during early boot, that is, during the time 5085 before the init task is spawned. 5086 5087 rcupdate.rcu_cpu_stall_timeout= [KNL] 5088 Set timeout for RCU CPU stall warning messages. 5089 The value is in seconds and the maximum allowed 5090 value is 300 seconds. 5091 5092 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 5093 Set timeout for expedited RCU CPU stall warning 5094 messages. The value is in milliseconds 5095 and the maximum allowed value is 21000 5096 milliseconds. Please note that this value is 5097 adjusted to an arch timer tick resolution. 5098 Setting this to zero causes the value from 5099 rcupdate.rcu_cpu_stall_timeout to be used (after 5100 conversion from seconds to milliseconds). 5101 5102 rcupdate.rcu_expedited= [KNL] 5103 Use expedited grace-period primitives, for 5104 example, synchronize_rcu_expedited() instead 5105 of synchronize_rcu(). This reduces latency, 5106 but can increase CPU utilization, degrade 5107 real-time latency, and degrade energy efficiency. 5108 No effect on CONFIG_TINY_RCU kernels. 5109 5110 rcupdate.rcu_normal= [KNL] 5111 Use only normal grace-period primitives, 5112 for example, synchronize_rcu() instead of 5113 synchronize_rcu_expedited(). This improves 5114 real-time latency, CPU utilization, and 5115 energy efficiency, but can expose users to 5116 increased grace-period latency. This parameter 5117 overrides rcupdate.rcu_expedited. No effect on 5118 CONFIG_TINY_RCU kernels. 5119 5120 rcupdate.rcu_normal_after_boot= [KNL] 5121 Once boot has completed (that is, after 5122 rcu_end_inkernel_boot() has been invoked), use 5123 only normal grace-period primitives. No effect 5124 on CONFIG_TINY_RCU kernels. 5125 5126 But note that CONFIG_PREEMPT_RT=y kernels enables 5127 this kernel boot parameter, forcibly setting 5128 it to the value one, that is, converting any 5129 post-boot attempt at an expedited RCU grace 5130 period to instead use normal non-expedited 5131 grace-period processing. 5132 5133 rcupdate.rcu_task_collapse_lim= [KNL] 5134 Set the maximum number of callbacks present 5135 at the beginning of a grace period that allows 5136 the RCU Tasks flavors to collapse back to using 5137 a single callback queue. This switching only 5138 occurs when rcupdate.rcu_task_enqueue_lim is 5139 set to the default value of -1. 5140 5141 rcupdate.rcu_task_contend_lim= [KNL] 5142 Set the minimum number of callback-queuing-time 5143 lock-contention events per jiffy required to 5144 cause the RCU Tasks flavors to switch to per-CPU 5145 callback queuing. This switching only occurs 5146 when rcupdate.rcu_task_enqueue_lim is set to 5147 the default value of -1. 5148 5149 rcupdate.rcu_task_enqueue_lim= [KNL] 5150 Set the number of callback queues to use for the 5151 RCU Tasks family of RCU flavors. The default 5152 of -1 allows this to be automatically (and 5153 dynamically) adjusted. This parameter is intended 5154 for use in testing. 5155 5156 rcupdate.rcu_task_ipi_delay= [KNL] 5157 Set time in jiffies during which RCU tasks will 5158 avoid sending IPIs, starting with the beginning 5159 of a given grace period. Setting a large 5160 number avoids disturbing real-time workloads, 5161 but lengthens grace periods. 5162 5163 rcupdate.rcu_task_stall_info= [KNL] 5164 Set initial timeout in jiffies for RCU task stall 5165 informational messages, which give some indication 5166 of the problem for those not patient enough to 5167 wait for ten minutes. Informational messages are 5168 only printed prior to the stall-warning message 5169 for a given grace period. Disable with a value 5170 less than or equal to zero. Defaults to ten 5171 seconds. A change in value does not take effect 5172 until the beginning of the next grace period. 5173 5174 rcupdate.rcu_task_stall_info_mult= [KNL] 5175 Multiplier for time interval between successive 5176 RCU task stall informational messages for a given 5177 RCU tasks grace period. This value is clamped 5178 to one through ten, inclusive. It defaults to 5179 the value three, so that the first informational 5180 message is printed 10 seconds into the grace 5181 period, the second at 40 seconds, the third at 5182 160 seconds, and then the stall warning at 600 5183 seconds would prevent a fourth at 640 seconds. 5184 5185 rcupdate.rcu_task_stall_timeout= [KNL] 5186 Set timeout in jiffies for RCU task stall 5187 warning messages. Disable with a value less 5188 than or equal to zero. Defaults to ten minutes. 5189 A change in value does not take effect until 5190 the beginning of the next grace period. 5191 5192 rcupdate.rcu_self_test= [KNL] 5193 Run the RCU early boot self tests 5194 5195 rdinit= [KNL] 5196 Format: <full_path> 5197 Run specified binary instead of /init from the ramdisk, 5198 used for early userspace startup. See initrd. 5199 5200 rdrand= [X86] 5201 force - Override the decision by the kernel to hide the 5202 advertisement of RDRAND support (this affects 5203 certain AMD processors because of buggy BIOS 5204 support, specifically around the suspend/resume 5205 path). 5206 5207 rdt= [HW,X86,RDT] 5208 Turn on/off individual RDT features. List is: 5209 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 5210 mba. 5211 E.g. to turn on cmt and turn off mba use: 5212 rdt=cmt,!mba 5213 5214 reboot= [KNL] 5215 Format (x86 or x86_64): 5216 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 5217 [[,]s[mp]#### \ 5218 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 5219 [[,]f[orce] 5220 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 5221 (prefix with 'panic_' to set mode for panic 5222 reboot only), 5223 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 5224 reboot_force is either force or not specified, 5225 reboot_cpu is s[mp]#### with #### being the processor 5226 to be used for rebooting. 5227 5228 refscale.holdoff= [KNL] 5229 Set test-start holdoff period. The purpose of 5230 this parameter is to delay the start of the 5231 test until boot completes in order to avoid 5232 interference. 5233 5234 refscale.loops= [KNL] 5235 Set the number of loops over the synchronization 5236 primitive under test. Increasing this number 5237 reduces noise due to loop start/end overhead, 5238 but the default has already reduced the per-pass 5239 noise to a handful of picoseconds on ca. 2020 5240 x86 laptops. 5241 5242 refscale.nreaders= [KNL] 5243 Set number of readers. The default value of -1 5244 selects N, where N is roughly 75% of the number 5245 of CPUs. A value of zero is an interesting choice. 5246 5247 refscale.nruns= [KNL] 5248 Set number of runs, each of which is dumped onto 5249 the console log. 5250 5251 refscale.readdelay= [KNL] 5252 Set the read-side critical-section duration, 5253 measured in microseconds. 5254 5255 refscale.scale_type= [KNL] 5256 Specify the read-protection implementation to test. 5257 5258 refscale.shutdown= [KNL] 5259 Shut down the system at the end of the performance 5260 test. This defaults to 1 (shut it down) when 5261 refscale is built into the kernel and to 0 (leave 5262 it running) when refscale is built as a module. 5263 5264 refscale.verbose= [KNL] 5265 Enable additional printk() statements. 5266 5267 refscale.verbose_batched= [KNL] 5268 Batch the additional printk() statements. If zero 5269 (the default) or negative, print everything. Otherwise, 5270 print every Nth verbose statement, where N is the value 5271 specified. 5272 5273 relax_domain_level= 5274 [KNL, SMP] Set scheduler's default relax_domain_level. 5275 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 5276 5277 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 5278 Format: <base1>,<size1>[,<base2>,<size2>,...] 5279 Reserve I/O ports or memory so the kernel won't use 5280 them. If <base> is less than 0x10000, the region 5281 is assumed to be I/O ports; otherwise it is memory. 5282 5283 reservetop= [X86-32] 5284 Format: nn[KMG] 5285 Reserves a hole at the top of the kernel virtual 5286 address space. 5287 5288 reset_devices [KNL] Force drivers to reset the underlying device 5289 during initialization. 5290 5291 resume= [SWSUSP] 5292 Specify the partition device for software suspend 5293 Format: 5294 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 5295 5296 resume_offset= [SWSUSP] 5297 Specify the offset from the beginning of the partition 5298 given by "resume=" at which the swap header is located, 5299 in <PAGE_SIZE> units (needed only for swap files). 5300 See Documentation/power/swsusp-and-swap-files.rst 5301 5302 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 5303 read the resume files 5304 5305 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 5306 Useful for devices that are detected asynchronously 5307 (e.g. USB and MMC devices). 5308 5309 retain_initrd [RAM] Keep initrd memory after extraction 5310 5311 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 5312 Speculative Code Execution with Return Instructions) 5313 vulnerability. 5314 5315 AMD-based UNRET and IBPB mitigations alone do not stop 5316 sibling threads from influencing the predictions of other 5317 sibling threads. For that reason, STIBP is used on pro- 5318 cessors that support it, and mitigate SMT on processors 5319 that don't. 5320 5321 off - no mitigation 5322 auto - automatically select a migitation 5323 auto,nosmt - automatically select a mitigation, 5324 disabling SMT if necessary for 5325 the full mitigation (only on Zen1 5326 and older without STIBP). 5327 ibpb - On AMD, mitigate short speculation 5328 windows on basic block boundaries too. 5329 Safe, highest perf impact. It also 5330 enables STIBP if present. Not suitable 5331 on Intel. 5332 ibpb,nosmt - Like "ibpb" above but will disable SMT 5333 when STIBP is not available. This is 5334 the alternative for systems which do not 5335 have STIBP. 5336 unret - Force enable untrained return thunks, 5337 only effective on AMD f15h-f17h based 5338 systems. 5339 unret,nosmt - Like unret, but will disable SMT when STIBP 5340 is not available. This is the alternative for 5341 systems which do not have STIBP. 5342 5343 Selecting 'auto' will choose a mitigation method at run 5344 time according to the CPU. 5345 5346 Not specifying this option is equivalent to retbleed=auto. 5347 5348 rfkill.default_state= 5349 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 5350 etc. communication is blocked by default. 5351 1 Unblocked. 5352 5353 rfkill.master_switch_mode= 5354 0 The "airplane mode" button does nothing. 5355 1 The "airplane mode" button toggles between everything 5356 blocked and the previous configuration. 5357 2 The "airplane mode" button toggles between everything 5358 blocked and everything unblocked. 5359 5360 rhash_entries= [KNL,NET] 5361 Set number of hash buckets for route cache 5362 5363 ring3mwait=disable 5364 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 5365 CPUs. 5366 5367 ro [KNL] Mount root device read-only on boot 5368 5369 rodata= [KNL] 5370 on Mark read-only kernel memory as read-only (default). 5371 off Leave read-only kernel memory writable for debugging. 5372 full Mark read-only kernel memory and aliases as read-only 5373 [arm64] 5374 5375 rockchip.usb_uart 5376 Enable the uart passthrough on the designated usb port 5377 on Rockchip SoCs. When active, the signals of the 5378 debug-uart get routed to the D+ and D- pins of the usb 5379 port and the regular usb controller gets disabled. 5380 5381 root= [KNL] Root filesystem 5382 See name_to_dev_t comment in init/do_mounts.c. 5383 5384 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 5385 mount the root filesystem 5386 5387 rootflags= [KNL] Set root filesystem mount option string 5388 5389 rootfstype= [KNL] Set root filesystem type 5390 5391 rootwait [KNL] Wait (indefinitely) for root device to show up. 5392 Useful for devices that are detected asynchronously 5393 (e.g. USB and MMC devices). 5394 5395 rproc_mem=nn[KMG][@address] 5396 [KNL,ARM,CMA] Remoteproc physical memory block. 5397 Memory area to be used by remote processor image, 5398 managed by CMA. 5399 5400 rw [KNL] Mount root device read-write on boot 5401 5402 S [KNL] Run init in single mode 5403 5404 s390_iommu= [HW,S390] 5405 Set s390 IOTLB flushing mode 5406 strict 5407 With strict flushing every unmap operation will result in 5408 an IOTLB flush. Default is lazy flushing before reuse, 5409 which is faster. 5410 5411 s390_iommu_aperture= [KNL,S390] 5412 Specifies the size of the per device DMA address space 5413 accessible through the DMA and IOMMU APIs as a decimal 5414 factor of the size of main memory. 5415 The default is 1 meaning that one can concurrently use 5416 as many DMA addresses as physical memory is installed, 5417 if supported by hardware, and thus map all of memory 5418 once. With a value of 2 one can map all of memory twice 5419 and so on. As a special case a factor of 0 imposes no 5420 restrictions other than those given by hardware at the 5421 cost of significant additional memory use for tables. 5422 5423 sa1100ir [NET] 5424 See drivers/net/irda/sa1100_ir.c. 5425 5426 sched_verbose [KNL] Enables verbose scheduler debug messages. 5427 5428 schedstats= [KNL,X86] Enable or disable scheduled statistics. 5429 Allowed values are enable and disable. This feature 5430 incurs a small amount of overhead in the scheduler 5431 but is useful for debugging and performance tuning. 5432 5433 sched_thermal_decay_shift= 5434 [KNL, SMP] Set a decay shift for scheduler thermal 5435 pressure signal. Thermal pressure signal follows the 5436 default decay period of other scheduler pelt 5437 signals(usually 32 ms but configurable). Setting 5438 sched_thermal_decay_shift will left shift the decay 5439 period for the thermal pressure signal by the shift 5440 value. 5441 i.e. with the default pelt decay period of 32 ms 5442 sched_thermal_decay_shift thermal pressure decay pr 5443 1 64 ms 5444 2 128 ms 5445 and so on. 5446 Format: integer between 0 and 10 5447 Default is 0. 5448 5449 scftorture.holdoff= [KNL] 5450 Number of seconds to hold off before starting 5451 test. Defaults to zero for module insertion and 5452 to 10 seconds for built-in smp_call_function() 5453 tests. 5454 5455 scftorture.longwait= [KNL] 5456 Request ridiculously long waits randomly selected 5457 up to the chosen limit in seconds. Zero (the 5458 default) disables this feature. Please note 5459 that requesting even small non-zero numbers of 5460 seconds can result in RCU CPU stall warnings, 5461 softlockup complaints, and so on. 5462 5463 scftorture.nthreads= [KNL] 5464 Number of kthreads to spawn to invoke the 5465 smp_call_function() family of functions. 5466 The default of -1 specifies a number of kthreads 5467 equal to the number of CPUs. 5468 5469 scftorture.onoff_holdoff= [KNL] 5470 Number seconds to wait after the start of the 5471 test before initiating CPU-hotplug operations. 5472 5473 scftorture.onoff_interval= [KNL] 5474 Number seconds to wait between successive 5475 CPU-hotplug operations. Specifying zero (which 5476 is the default) disables CPU-hotplug operations. 5477 5478 scftorture.shutdown_secs= [KNL] 5479 The number of seconds following the start of the 5480 test after which to shut down the system. The 5481 default of zero avoids shutting down the system. 5482 Non-zero values are useful for automated tests. 5483 5484 scftorture.stat_interval= [KNL] 5485 The number of seconds between outputting the 5486 current test statistics to the console. A value 5487 of zero disables statistics output. 5488 5489 scftorture.stutter_cpus= [KNL] 5490 The number of jiffies to wait between each change 5491 to the set of CPUs under test. 5492 5493 scftorture.use_cpus_read_lock= [KNL] 5494 Use use_cpus_read_lock() instead of the default 5495 preempt_disable() to disable CPU hotplug 5496 while invoking one of the smp_call_function*() 5497 functions. 5498 5499 scftorture.verbose= [KNL] 5500 Enable additional printk() statements. 5501 5502 scftorture.weight_single= [KNL] 5503 The probability weighting to use for the 5504 smp_call_function_single() function with a zero 5505 "wait" parameter. A value of -1 selects the 5506 default if all other weights are -1. However, 5507 if at least one weight has some other value, a 5508 value of -1 will instead select a weight of zero. 5509 5510 scftorture.weight_single_wait= [KNL] 5511 The probability weighting to use for the 5512 smp_call_function_single() function with a 5513 non-zero "wait" parameter. See weight_single. 5514 5515 scftorture.weight_many= [KNL] 5516 The probability weighting to use for the 5517 smp_call_function_many() function with a zero 5518 "wait" parameter. See weight_single. 5519 Note well that setting a high probability for 5520 this weighting can place serious IPI load 5521 on the system. 5522 5523 scftorture.weight_many_wait= [KNL] 5524 The probability weighting to use for the 5525 smp_call_function_many() function with a 5526 non-zero "wait" parameter. See weight_single 5527 and weight_many. 5528 5529 scftorture.weight_all= [KNL] 5530 The probability weighting to use for the 5531 smp_call_function_all() function with a zero 5532 "wait" parameter. See weight_single and 5533 weight_many. 5534 5535 scftorture.weight_all_wait= [KNL] 5536 The probability weighting to use for the 5537 smp_call_function_all() function with a 5538 non-zero "wait" parameter. See weight_single 5539 and weight_many. 5540 5541 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 5542 xtime_lock contention on larger systems, and/or RCU lock 5543 contention on all systems with CONFIG_MAXSMP set. 5544 Format: { "0" | "1" } 5545 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 5546 1 -- enable. 5547 Note: increases power consumption, thus should only be 5548 enabled if running jitter sensitive (HPC/RT) workloads. 5549 5550 security= [SECURITY] Choose a legacy "major" security module to 5551 enable at boot. This has been deprecated by the 5552 "lsm=" parameter. 5553 5554 selinux= [SELINUX] Disable or enable SELinux at boot time. 5555 Format: { "0" | "1" } 5556 See security/selinux/Kconfig help text. 5557 0 -- disable. 5558 1 -- enable. 5559 Default value is 1. 5560 5561 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 5562 Format: { "0" | "1" } 5563 See security/apparmor/Kconfig help text 5564 0 -- disable. 5565 1 -- enable. 5566 Default value is set via kernel config option. 5567 5568 serialnumber [BUGS=X86-32] 5569 5570 sev=option[,option...] [X86-64] See Documentation/x86/x86_64/boot-options.rst 5571 5572 shapers= [NET] 5573 Maximal number of shapers. 5574 5575 simeth= [IA-64] 5576 simscsi= 5577 5578 slram= [HW,MTD] 5579 5580 slab_merge [MM] 5581 Enable merging of slabs with similar size when the 5582 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 5583 5584 slab_nomerge [MM] 5585 Disable merging of slabs with similar size. May be 5586 necessary if there is some reason to distinguish 5587 allocs to different slabs, especially in hardened 5588 environments where the risk of heap overflows and 5589 layout control by attackers can usually be 5590 frustrated by disabling merging. This will reduce 5591 most of the exposure of a heap attack to a single 5592 cache (risks via metadata attacks are mostly 5593 unchanged). Debug options disable merging on their 5594 own. 5595 For more information see Documentation/mm/slub.rst. 5596 5597 slab_max_order= [MM, SLAB] 5598 Determines the maximum allowed order for slabs. 5599 A high setting may cause OOMs due to memory 5600 fragmentation. Defaults to 1 for systems with 5601 more than 32MB of RAM, 0 otherwise. 5602 5603 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 5604 Enabling slub_debug allows one to determine the 5605 culprit if slab objects become corrupted. Enabling 5606 slub_debug can create guard zones around objects and 5607 may poison objects when not in use. Also tracks the 5608 last alloc / free. For more information see 5609 Documentation/mm/slub.rst. 5610 5611 slub_max_order= [MM, SLUB] 5612 Determines the maximum allowed order for slabs. 5613 A high setting may cause OOMs due to memory 5614 fragmentation. For more information see 5615 Documentation/mm/slub.rst. 5616 5617 slub_min_objects= [MM, SLUB] 5618 The minimum number of objects per slab. SLUB will 5619 increase the slab order up to slub_max_order to 5620 generate a sufficiently large slab able to contain 5621 the number of objects indicated. The higher the number 5622 of objects the smaller the overhead of tracking slabs 5623 and the less frequently locks need to be acquired. 5624 For more information see Documentation/mm/slub.rst. 5625 5626 slub_min_order= [MM, SLUB] 5627 Determines the minimum page order for slabs. Must be 5628 lower than slub_max_order. 5629 For more information see Documentation/mm/slub.rst. 5630 5631 slub_merge [MM, SLUB] 5632 Same with slab_merge. 5633 5634 slub_nomerge [MM, SLUB] 5635 Same with slab_nomerge. This is supported for legacy. 5636 See slab_nomerge for more information. 5637 5638 smart2= [HW] 5639 Format: <io1>[,<io2>[,...,<io8>]] 5640 5641 smp.csd_lock_timeout= [KNL] 5642 Specify the period of time in milliseconds 5643 that smp_call_function() and friends will wait 5644 for a CPU to release the CSD lock. This is 5645 useful when diagnosing bugs involving CPUs 5646 disabling interrupts for extended periods 5647 of time. Defaults to 5,000 milliseconds, and 5648 setting a value of zero disables this feature. 5649 This feature may be more efficiently disabled 5650 using the csdlock_debug- kernel parameter. 5651 5652 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 5653 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 5654 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 5655 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 5656 smsc-ircc2.ircc_irq= [HW] IRQ line 5657 smsc-ircc2.ircc_dma= [HW] DMA channel 5658 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 5659 0: Toshiba Satellite 1800 (GP data pin select) 5660 1: Fast pin select (default) 5661 2: ATC IRMode 5662 5663 smt= [KNL,S390] Set the maximum number of threads (logical 5664 CPUs) to use per physical CPU on systems capable of 5665 symmetric multithreading (SMT). Will be capped to the 5666 actual hardware limit. 5667 Format: <integer> 5668 Default: -1 (no limit) 5669 5670 softlockup_panic= 5671 [KNL] Should the soft-lockup detector generate panics. 5672 Format: 0 | 1 5673 5674 A value of 1 instructs the soft-lockup detector 5675 to panic the machine when a soft-lockup occurs. It is 5676 also controlled by the kernel.softlockup_panic sysctl 5677 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 5678 respective build-time switch to that functionality. 5679 5680 softlockup_all_cpu_backtrace= 5681 [KNL] Should the soft-lockup detector generate 5682 backtraces on all cpus. 5683 Format: 0 | 1 5684 5685 sonypi.*= [HW] Sony Programmable I/O Control Device driver 5686 See Documentation/admin-guide/laptops/sonypi.rst 5687 5688 spectre_v2= [X86] Control mitigation of Spectre variant 2 5689 (indirect branch speculation) vulnerability. 5690 The default operation protects the kernel from 5691 user space attacks. 5692 5693 on - unconditionally enable, implies 5694 spectre_v2_user=on 5695 off - unconditionally disable, implies 5696 spectre_v2_user=off 5697 auto - kernel detects whether your CPU model is 5698 vulnerable 5699 5700 Selecting 'on' will, and 'auto' may, choose a 5701 mitigation method at run time according to the 5702 CPU, the available microcode, the setting of the 5703 CONFIG_RETPOLINE configuration option, and the 5704 compiler with which the kernel was built. 5705 5706 Selecting 'on' will also enable the mitigation 5707 against user space to user space task attacks. 5708 5709 Selecting 'off' will disable both the kernel and 5710 the user space protections. 5711 5712 Specific mitigations can also be selected manually: 5713 5714 retpoline - replace indirect branches 5715 retpoline,generic - Retpolines 5716 retpoline,lfence - LFENCE; indirect branch 5717 retpoline,amd - alias for retpoline,lfence 5718 eibrs - enhanced IBRS 5719 eibrs,retpoline - enhanced IBRS + Retpolines 5720 eibrs,lfence - enhanced IBRS + LFENCE 5721 ibrs - use IBRS to protect kernel 5722 5723 Not specifying this option is equivalent to 5724 spectre_v2=auto. 5725 5726 spectre_v2_user= 5727 [X86] Control mitigation of Spectre variant 2 5728 (indirect branch speculation) vulnerability between 5729 user space tasks 5730 5731 on - Unconditionally enable mitigations. Is 5732 enforced by spectre_v2=on 5733 5734 off - Unconditionally disable mitigations. Is 5735 enforced by spectre_v2=off 5736 5737 prctl - Indirect branch speculation is enabled, 5738 but mitigation can be enabled via prctl 5739 per thread. The mitigation control state 5740 is inherited on fork. 5741 5742 prctl,ibpb 5743 - Like "prctl" above, but only STIBP is 5744 controlled per thread. IBPB is issued 5745 always when switching between different user 5746 space processes. 5747 5748 seccomp 5749 - Same as "prctl" above, but all seccomp 5750 threads will enable the mitigation unless 5751 they explicitly opt out. 5752 5753 seccomp,ibpb 5754 - Like "seccomp" above, but only STIBP is 5755 controlled per thread. IBPB is issued 5756 always when switching between different 5757 user space processes. 5758 5759 auto - Kernel selects the mitigation depending on 5760 the available CPU features and vulnerability. 5761 5762 Default mitigation: "prctl" 5763 5764 Not specifying this option is equivalent to 5765 spectre_v2_user=auto. 5766 5767 spec_store_bypass_disable= 5768 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 5769 (Speculative Store Bypass vulnerability) 5770 5771 Certain CPUs are vulnerable to an exploit against a 5772 a common industry wide performance optimization known 5773 as "Speculative Store Bypass" in which recent stores 5774 to the same memory location may not be observed by 5775 later loads during speculative execution. The idea 5776 is that such stores are unlikely and that they can 5777 be detected prior to instruction retirement at the 5778 end of a particular speculation execution window. 5779 5780 In vulnerable processors, the speculatively forwarded 5781 store can be used in a cache side channel attack, for 5782 example to read memory to which the attacker does not 5783 directly have access (e.g. inside sandboxed code). 5784 5785 This parameter controls whether the Speculative Store 5786 Bypass optimization is used. 5787 5788 On x86 the options are: 5789 5790 on - Unconditionally disable Speculative Store Bypass 5791 off - Unconditionally enable Speculative Store Bypass 5792 auto - Kernel detects whether the CPU model contains an 5793 implementation of Speculative Store Bypass and 5794 picks the most appropriate mitigation. If the 5795 CPU is not vulnerable, "off" is selected. If the 5796 CPU is vulnerable the default mitigation is 5797 architecture and Kconfig dependent. See below. 5798 prctl - Control Speculative Store Bypass per thread 5799 via prctl. Speculative Store Bypass is enabled 5800 for a process by default. The state of the control 5801 is inherited on fork. 5802 seccomp - Same as "prctl" above, but all seccomp threads 5803 will disable SSB unless they explicitly opt out. 5804 5805 Default mitigations: 5806 X86: "prctl" 5807 5808 On powerpc the options are: 5809 5810 on,auto - On Power8 and Power9 insert a store-forwarding 5811 barrier on kernel entry and exit. On Power7 5812 perform a software flush on kernel entry and 5813 exit. 5814 off - No action. 5815 5816 Not specifying this option is equivalent to 5817 spec_store_bypass_disable=auto. 5818 5819 spia_io_base= [HW,MTD] 5820 spia_fio_base= 5821 spia_pedr= 5822 spia_peddr= 5823 5824 split_lock_detect= 5825 [X86] Enable split lock detection or bus lock detection 5826 5827 When enabled (and if hardware support is present), atomic 5828 instructions that access data across cache line 5829 boundaries will result in an alignment check exception 5830 for split lock detection or a debug exception for 5831 bus lock detection. 5832 5833 off - not enabled 5834 5835 warn - the kernel will emit rate-limited warnings 5836 about applications triggering the #AC 5837 exception or the #DB exception. This mode is 5838 the default on CPUs that support split lock 5839 detection or bus lock detection. Default 5840 behavior is by #AC if both features are 5841 enabled in hardware. 5842 5843 fatal - the kernel will send SIGBUS to applications 5844 that trigger the #AC exception or the #DB 5845 exception. Default behavior is by #AC if 5846 both features are enabled in hardware. 5847 5848 ratelimit:N - 5849 Set system wide rate limit to N bus locks 5850 per second for bus lock detection. 5851 0 < N <= 1000. 5852 5853 N/A for split lock detection. 5854 5855 5856 If an #AC exception is hit in the kernel or in 5857 firmware (i.e. not while executing in user mode) 5858 the kernel will oops in either "warn" or "fatal" 5859 mode. 5860 5861 #DB exception for bus lock is triggered only when 5862 CPL > 0. 5863 5864 srbds= [X86,INTEL] 5865 Control the Special Register Buffer Data Sampling 5866 (SRBDS) mitigation. 5867 5868 Certain CPUs are vulnerable to an MDS-like 5869 exploit which can leak bits from the random 5870 number generator. 5871 5872 By default, this issue is mitigated by 5873 microcode. However, the microcode fix can cause 5874 the RDRAND and RDSEED instructions to become 5875 much slower. Among other effects, this will 5876 result in reduced throughput from /dev/urandom. 5877 5878 The microcode mitigation can be disabled with 5879 the following option: 5880 5881 off: Disable mitigation and remove 5882 performance impact to RDRAND and RDSEED 5883 5884 srcutree.big_cpu_lim [KNL] 5885 Specifies the number of CPUs constituting a 5886 large system, such that srcu_struct structures 5887 should immediately allocate an srcu_node array. 5888 This kernel-boot parameter defaults to 128, 5889 but takes effect only when the low-order four 5890 bits of srcutree.convert_to_big is equal to 3 5891 (decide at boot). 5892 5893 srcutree.convert_to_big [KNL] 5894 Specifies under what conditions an SRCU tree 5895 srcu_struct structure will be converted to big 5896 form, that is, with an rcu_node tree: 5897 5898 0: Never. 5899 1: At init_srcu_struct() time. 5900 2: When rcutorture decides to. 5901 3: Decide at boot time (default). 5902 0x1X: Above plus if high contention. 5903 5904 Either way, the srcu_node tree will be sized based 5905 on the actual runtime number of CPUs (nr_cpu_ids) 5906 instead of the compile-time CONFIG_NR_CPUS. 5907 5908 srcutree.counter_wrap_check [KNL] 5909 Specifies how frequently to check for 5910 grace-period sequence counter wrap for the 5911 srcu_data structure's ->srcu_gp_seq_needed field. 5912 The greater the number of bits set in this kernel 5913 parameter, the less frequently counter wrap will 5914 be checked for. Note that the bottom two bits 5915 are ignored. 5916 5917 srcutree.exp_holdoff [KNL] 5918 Specifies how many nanoseconds must elapse 5919 since the end of the last SRCU grace period for 5920 a given srcu_struct until the next normal SRCU 5921 grace period will be considered for automatic 5922 expediting. Set to zero to disable automatic 5923 expediting. 5924 5925 srcutree.srcu_max_nodelay [KNL] 5926 Specifies the number of no-delay instances 5927 per jiffy for which the SRCU grace period 5928 worker thread will be rescheduled with zero 5929 delay. Beyond this limit, worker thread will 5930 be rescheduled with a sleep delay of one jiffy. 5931 5932 srcutree.srcu_max_nodelay_phase [KNL] 5933 Specifies the per-grace-period phase, number of 5934 non-sleeping polls of readers. Beyond this limit, 5935 grace period worker thread will be rescheduled 5936 with a sleep delay of one jiffy, between each 5937 rescan of the readers, for a grace period phase. 5938 5939 srcutree.srcu_retry_check_delay [KNL] 5940 Specifies number of microseconds of non-sleeping 5941 delay between each non-sleeping poll of readers. 5942 5943 srcutree.small_contention_lim [KNL] 5944 Specifies the number of update-side contention 5945 events per jiffy will be tolerated before 5946 initiating a conversion of an srcu_struct 5947 structure to big form. Note that the value of 5948 srcutree.convert_to_big must have the 0x10 bit 5949 set for contention-based conversions to occur. 5950 5951 ssbd= [ARM64,HW] 5952 Speculative Store Bypass Disable control 5953 5954 On CPUs that are vulnerable to the Speculative 5955 Store Bypass vulnerability and offer a 5956 firmware based mitigation, this parameter 5957 indicates how the mitigation should be used: 5958 5959 force-on: Unconditionally enable mitigation for 5960 for both kernel and userspace 5961 force-off: Unconditionally disable mitigation for 5962 for both kernel and userspace 5963 kernel: Always enable mitigation in the 5964 kernel, and offer a prctl interface 5965 to allow userspace to register its 5966 interest in being mitigated too. 5967 5968 stack_guard_gap= [MM] 5969 override the default stack gap protection. The value 5970 is in page units and it defines how many pages prior 5971 to (for stacks growing down) resp. after (for stacks 5972 growing up) the main stack are reserved for no other 5973 mapping. Default value is 256 pages. 5974 5975 stack_depot_disable= [KNL] 5976 Setting this to true through kernel command line will 5977 disable the stack depot thereby saving the static memory 5978 consumed by the stack hash table. By default this is set 5979 to false. 5980 5981 stacktrace [FTRACE] 5982 Enabled the stack tracer on boot up. 5983 5984 stacktrace_filter=[function-list] 5985 [FTRACE] Limit the functions that the stack tracer 5986 will trace at boot up. function-list is a comma-separated 5987 list of functions. This list can be changed at run 5988 time by the stack_trace_filter file in the debugfs 5989 tracing directory. Note, this enables stack tracing 5990 and the stacktrace above is not needed. 5991 5992 sti= [PARISC,HW] 5993 Format: <num> 5994 Set the STI (builtin display/keyboard on the HP-PARISC 5995 machines) console (graphic card) which should be used 5996 as the initial boot-console. 5997 See also comment in drivers/video/console/sticore.c. 5998 5999 sti_font= [HW] 6000 See comment in drivers/video/console/sticore.c. 6001 6002 stifb= [HW] 6003 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 6004 6005 strict_sas_size= 6006 [X86] 6007 Format: <bool> 6008 Enable or disable strict sigaltstack size checks 6009 against the required signal frame size which 6010 depends on the supported FPU features. This can 6011 be used to filter out binaries which have 6012 not yet been made aware of AT_MINSIGSTKSZ. 6013 6014 sunrpc.min_resvport= 6015 sunrpc.max_resvport= 6016 [NFS,SUNRPC] 6017 SunRPC servers often require that client requests 6018 originate from a privileged port (i.e. a port in the 6019 range 0 < portnr < 1024). 6020 An administrator who wishes to reserve some of these 6021 ports for other uses may adjust the range that the 6022 kernel's sunrpc client considers to be privileged 6023 using these two parameters to set the minimum and 6024 maximum port values. 6025 6026 sunrpc.svc_rpc_per_connection_limit= 6027 [NFS,SUNRPC] 6028 Limit the number of requests that the server will 6029 process in parallel from a single connection. 6030 The default value is 0 (no limit). 6031 6032 sunrpc.pool_mode= 6033 [NFS] 6034 Control how the NFS server code allocates CPUs to 6035 service thread pools. Depending on how many NICs 6036 you have and where their interrupts are bound, this 6037 option will affect which CPUs will do NFS serving. 6038 Note: this parameter cannot be changed while the 6039 NFS server is running. 6040 6041 auto the server chooses an appropriate mode 6042 automatically using heuristics 6043 global a single global pool contains all CPUs 6044 percpu one pool for each CPU 6045 pernode one pool for each NUMA node (equivalent 6046 to global on non-NUMA machines) 6047 6048 sunrpc.tcp_slot_table_entries= 6049 sunrpc.udp_slot_table_entries= 6050 [NFS,SUNRPC] 6051 Sets the upper limit on the number of simultaneous 6052 RPC calls that can be sent from the client to a 6053 server. Increasing these values may allow you to 6054 improve throughput, but will also increase the 6055 amount of memory reserved for use by the client. 6056 6057 suspend.pm_test_delay= 6058 [SUSPEND] 6059 Sets the number of seconds to remain in a suspend test 6060 mode before resuming the system (see 6061 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 6062 is set. Default value is 5. 6063 6064 svm= [PPC] 6065 Format: { on | off | y | n | 1 | 0 } 6066 This parameter controls use of the Protected 6067 Execution Facility on pSeries. 6068 6069 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 6070 Format: { <int> [,<int>] | force | noforce } 6071 <int> -- Number of I/O TLB slabs 6072 <int> -- Second integer after comma. Number of swiotlb 6073 areas with their own lock. Will be rounded up 6074 to a power of 2. 6075 force -- force using of bounce buffers even if they 6076 wouldn't be automatically used by the kernel 6077 noforce -- Never use bounce buffers (for debugging) 6078 6079 switches= [HW,M68k] 6080 6081 sysctl.*= [KNL] 6082 Set a sysctl parameter, right before loading the init 6083 process, as if the value was written to the respective 6084 /proc/sys/... file. Both '.' and '/' are recognized as 6085 separators. Unrecognized parameters and invalid values 6086 are reported in the kernel log. Sysctls registered 6087 later by a loaded module cannot be set this way. 6088 Example: sysctl.vm.swappiness=40 6089 6090 sysfs.deprecated=0|1 [KNL] 6091 Enable/disable old style sysfs layout for old udev 6092 on older distributions. When this option is enabled 6093 very new udev will not work anymore. When this option 6094 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 6095 in older udev will not work anymore. 6096 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 6097 the kernel configuration. 6098 6099 sysrq_always_enabled 6100 [KNL] 6101 Ignore sysrq setting - this boot parameter will 6102 neutralize any effect of /proc/sys/kernel/sysrq. 6103 Useful for debugging. 6104 6105 tcpmhash_entries= [KNL,NET] 6106 Set the number of tcp_metrics_hash slots. 6107 Default value is 8192 or 16384 depending on total 6108 ram pages. This is used to specify the TCP metrics 6109 cache size. See Documentation/networking/ip-sysctl.rst 6110 "tcp_no_metrics_save" section for more details. 6111 6112 tdfx= [HW,DRM] 6113 6114 test_suspend= [SUSPEND] 6115 Format: { "mem" | "standby" | "freeze" }[,N] 6116 Specify "mem" (for Suspend-to-RAM) or "standby" (for 6117 standby suspend) or "freeze" (for suspend type freeze) 6118 as the system sleep state during system startup with 6119 the optional capability to repeat N number of times. 6120 The system is woken from this state using a 6121 wakeup-capable RTC alarm. 6122 6123 thash_entries= [KNL,NET] 6124 Set number of hash buckets for TCP connection 6125 6126 thermal.act= [HW,ACPI] 6127 -1: disable all active trip points in all thermal zones 6128 <degrees C>: override all lowest active trip points 6129 6130 thermal.crt= [HW,ACPI] 6131 -1: disable all critical trip points in all thermal zones 6132 <degrees C>: override all critical trip points 6133 6134 thermal.nocrt= [HW,ACPI] 6135 Set to disable actions on ACPI thermal zone 6136 critical and hot trip points. 6137 6138 thermal.off= [HW,ACPI] 6139 1: disable ACPI thermal control 6140 6141 thermal.psv= [HW,ACPI] 6142 -1: disable all passive trip points 6143 <degrees C>: override all passive trip points to this 6144 value 6145 6146 thermal.tzp= [HW,ACPI] 6147 Specify global default ACPI thermal zone polling rate 6148 <deci-seconds>: poll all this frequency 6149 0: no polling (default) 6150 6151 threadirqs [KNL] 6152 Force threading of all interrupt handlers except those 6153 marked explicitly IRQF_NO_THREAD. 6154 6155 topology= [S390] 6156 Format: {off | on} 6157 Specify if the kernel should make use of the cpu 6158 topology information if the hardware supports this. 6159 The scheduler will make use of this information and 6160 e.g. base its process migration decisions on it. 6161 Default is on. 6162 6163 topology_updates= [KNL, PPC, NUMA] 6164 Format: {off} 6165 Specify if the kernel should ignore (off) 6166 topology updates sent by the hypervisor to this 6167 LPAR. 6168 6169 torture.disable_onoff_at_boot= [KNL] 6170 Prevent the CPU-hotplug component of torturing 6171 until after init has spawned. 6172 6173 torture.ftrace_dump_at_shutdown= [KNL] 6174 Dump the ftrace buffer at torture-test shutdown, 6175 even if there were no errors. This can be a 6176 very costly operation when many torture tests 6177 are running concurrently, especially on systems 6178 with rotating-rust storage. 6179 6180 torture.verbose_sleep_frequency= [KNL] 6181 Specifies how many verbose printk()s should be 6182 emitted between each sleep. The default of zero 6183 disables verbose-printk() sleeping. 6184 6185 torture.verbose_sleep_duration= [KNL] 6186 Duration of each verbose-printk() sleep in jiffies. 6187 6188 tp720= [HW,PS2] 6189 6190 tpm_suspend_pcr=[HW,TPM] 6191 Format: integer pcr id 6192 Specify that at suspend time, the tpm driver 6193 should extend the specified pcr with zeros, 6194 as a workaround for some chips which fail to 6195 flush the last written pcr on TPM_SaveState. 6196 This will guarantee that all the other pcrs 6197 are saved. 6198 6199 tp_printk [FTRACE] 6200 Have the tracepoints sent to printk as well as the 6201 tracing ring buffer. This is useful for early boot up 6202 where the system hangs or reboots and does not give the 6203 option for reading the tracing buffer or performing a 6204 ftrace_dump_on_oops. 6205 6206 To turn off having tracepoints sent to printk, 6207 echo 0 > /proc/sys/kernel/tracepoint_printk 6208 Note, echoing 1 into this file without the 6209 tracepoint_printk kernel cmdline option has no effect. 6210 6211 The tp_printk_stop_on_boot (see below) can also be used 6212 to stop the printing of events to console at 6213 late_initcall_sync. 6214 6215 ** CAUTION ** 6216 6217 Having tracepoints sent to printk() and activating high 6218 frequency tracepoints such as irq or sched, can cause 6219 the system to live lock. 6220 6221 tp_printk_stop_on_boot [FTRACE] 6222 When tp_printk (above) is set, it can cause a lot of noise 6223 on the console. It may be useful to only include the 6224 printing of events during boot up, as user space may 6225 make the system inoperable. 6226 6227 This command line option will stop the printing of events 6228 to console at the late_initcall_sync() time frame. 6229 6230 trace_buf_size=nn[KMG] 6231 [FTRACE] will set tracing buffer size on each cpu. 6232 6233 trace_clock= [FTRACE] Set the clock used for tracing events 6234 at boot up. 6235 local - Use the per CPU time stamp counter 6236 (converted into nanoseconds). Fast, but 6237 depending on the architecture, may not be 6238 in sync between CPUs. 6239 global - Event time stamps are synchronize across 6240 CPUs. May be slower than the local clock, 6241 but better for some race conditions. 6242 counter - Simple counting of events (1, 2, ..) 6243 note, some counts may be skipped due to the 6244 infrastructure grabbing the clock more than 6245 once per event. 6246 uptime - Use jiffies as the time stamp. 6247 perf - Use the same clock that perf uses. 6248 mono - Use ktime_get_mono_fast_ns() for time stamps. 6249 mono_raw - Use ktime_get_raw_fast_ns() for time 6250 stamps. 6251 boot - Use ktime_get_boot_fast_ns() for time stamps. 6252 Architectures may add more clocks. See 6253 Documentation/trace/ftrace.rst for more details. 6254 6255 trace_event=[event-list] 6256 [FTRACE] Set and start specified trace events in order 6257 to facilitate early boot debugging. The event-list is a 6258 comma-separated list of trace events to enable. See 6259 also Documentation/trace/events.rst 6260 6261 trace_options=[option-list] 6262 [FTRACE] Enable or disable tracer options at boot. 6263 The option-list is a comma delimited list of options 6264 that can be enabled or disabled just as if you were 6265 to echo the option name into 6266 6267 /sys/kernel/debug/tracing/trace_options 6268 6269 For example, to enable stacktrace option (to dump the 6270 stack trace of each event), add to the command line: 6271 6272 trace_options=stacktrace 6273 6274 See also Documentation/trace/ftrace.rst "trace options" 6275 section. 6276 6277 traceoff_on_warning 6278 [FTRACE] enable this option to disable tracing when a 6279 warning is hit. This turns off "tracing_on". Tracing can 6280 be enabled again by echoing '1' into the "tracing_on" 6281 file located in /sys/kernel/debug/tracing/ 6282 6283 This option is useful, as it disables the trace before 6284 the WARNING dump is called, which prevents the trace to 6285 be filled with content caused by the warning output. 6286 6287 This option can also be set at run time via the sysctl 6288 option: kernel/traceoff_on_warning 6289 6290 transparent_hugepage= 6291 [KNL] 6292 Format: [always|madvise|never] 6293 Can be used to control the default behavior of the system 6294 with respect to transparent hugepages. 6295 See Documentation/admin-guide/mm/transhuge.rst 6296 for more details. 6297 6298 trusted.source= [KEYS] 6299 Format: <string> 6300 This parameter identifies the trust source as a backend 6301 for trusted keys implementation. Supported trust 6302 sources: 6303 - "tpm" 6304 - "tee" 6305 - "caam" 6306 If not specified then it defaults to iterating through 6307 the trust source list starting with TPM and assigns the 6308 first trust source as a backend which is initialized 6309 successfully during iteration. 6310 6311 trusted.rng= [KEYS] 6312 Format: <string> 6313 The RNG used to generate key material for trusted keys. 6314 Can be one of: 6315 - "kernel" 6316 - the same value as trusted.source: "tpm" or "tee" 6317 - "default" 6318 If not specified, "default" is used. In this case, 6319 the RNG's choice is left to each individual trust source. 6320 6321 tsc= Disable clocksource stability checks for TSC. 6322 Format: <string> 6323 [x86] reliable: mark tsc clocksource as reliable, this 6324 disables clocksource verification at runtime, as well 6325 as the stability checks done at bootup. Used to enable 6326 high-resolution timer mode on older hardware, and in 6327 virtualized environment. 6328 [x86] noirqtime: Do not use TSC to do irq accounting. 6329 Used to run time disable IRQ_TIME_ACCOUNTING on any 6330 platforms where RDTSC is slow and this accounting 6331 can add overhead. 6332 [x86] unstable: mark the TSC clocksource as unstable, this 6333 marks the TSC unconditionally unstable at bootup and 6334 avoids any further wobbles once the TSC watchdog notices. 6335 [x86] nowatchdog: disable clocksource watchdog. Used 6336 in situations with strict latency requirements (where 6337 interruptions from clocksource watchdog are not 6338 acceptable). 6339 6340 tsc_early_khz= [X86] Skip early TSC calibration and use the given 6341 value instead. Useful when the early TSC frequency discovery 6342 procedure is not reliable, such as on overclocked systems 6343 with CPUID.16h support and partial CPUID.15h support. 6344 Format: <unsigned int> 6345 6346 tsx= [X86] Control Transactional Synchronization 6347 Extensions (TSX) feature in Intel processors that 6348 support TSX control. 6349 6350 This parameter controls the TSX feature. The options are: 6351 6352 on - Enable TSX on the system. Although there are 6353 mitigations for all known security vulnerabilities, 6354 TSX has been known to be an accelerator for 6355 several previous speculation-related CVEs, and 6356 so there may be unknown security risks associated 6357 with leaving it enabled. 6358 6359 off - Disable TSX on the system. (Note that this 6360 option takes effect only on newer CPUs which are 6361 not vulnerable to MDS, i.e., have 6362 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 6363 the new IA32_TSX_CTRL MSR through a microcode 6364 update. This new MSR allows for the reliable 6365 deactivation of the TSX functionality.) 6366 6367 auto - Disable TSX if X86_BUG_TAA is present, 6368 otherwise enable TSX on the system. 6369 6370 Not specifying this option is equivalent to tsx=off. 6371 6372 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 6373 for more details. 6374 6375 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 6376 Abort (TAA) vulnerability. 6377 6378 Similar to Micro-architectural Data Sampling (MDS) 6379 certain CPUs that support Transactional 6380 Synchronization Extensions (TSX) are vulnerable to an 6381 exploit against CPU internal buffers which can forward 6382 information to a disclosure gadget under certain 6383 conditions. 6384 6385 In vulnerable processors, the speculatively forwarded 6386 data can be used in a cache side channel attack, to 6387 access data to which the attacker does not have direct 6388 access. 6389 6390 This parameter controls the TAA mitigation. The 6391 options are: 6392 6393 full - Enable TAA mitigation on vulnerable CPUs 6394 if TSX is enabled. 6395 6396 full,nosmt - Enable TAA mitigation and disable SMT on 6397 vulnerable CPUs. If TSX is disabled, SMT 6398 is not disabled because CPU is not 6399 vulnerable to cross-thread TAA attacks. 6400 off - Unconditionally disable TAA mitigation 6401 6402 On MDS-affected machines, tsx_async_abort=off can be 6403 prevented by an active MDS mitigation as both vulnerabilities 6404 are mitigated with the same mechanism so in order to disable 6405 this mitigation, you need to specify mds=off too. 6406 6407 Not specifying this option is equivalent to 6408 tsx_async_abort=full. On CPUs which are MDS affected 6409 and deploy MDS mitigation, TAA mitigation is not 6410 required and doesn't provide any additional 6411 mitigation. 6412 6413 For details see: 6414 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 6415 6416 turbografx.map[2|3]= [HW,JOY] 6417 TurboGraFX parallel port interface 6418 Format: 6419 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 6420 See also Documentation/input/devices/joystick-parport.rst 6421 6422 udbg-immortal [PPC] When debugging early kernel crashes that 6423 happen after console_init() and before a proper 6424 console driver takes over, this boot options might 6425 help "seeing" what's going on. 6426 6427 uhash_entries= [KNL,NET] 6428 Set number of hash buckets for UDP/UDP-Lite connections 6429 6430 uhci-hcd.ignore_oc= 6431 [USB] Ignore overcurrent events (default N). 6432 Some badly-designed motherboards generate lots of 6433 bogus events, for ports that aren't wired to 6434 anything. Set this parameter to avoid log spamming. 6435 Note that genuine overcurrent events won't be 6436 reported either. 6437 6438 unknown_nmi_panic 6439 [X86] Cause panic on unknown NMI. 6440 6441 usbcore.authorized_default= 6442 [USB] Default USB device authorization: 6443 (default -1 = authorized except for wireless USB, 6444 0 = not authorized, 1 = authorized, 2 = authorized 6445 if device connected to internal port) 6446 6447 usbcore.autosuspend= 6448 [USB] The autosuspend time delay (in seconds) used 6449 for newly-detected USB devices (default 2). This 6450 is the time required before an idle device will be 6451 autosuspended. Devices for which the delay is set 6452 to a negative value won't be autosuspended at all. 6453 6454 usbcore.usbfs_snoop= 6455 [USB] Set to log all usbfs traffic (default 0 = off). 6456 6457 usbcore.usbfs_snoop_max= 6458 [USB] Maximum number of bytes to snoop in each URB 6459 (default = 65536). 6460 6461 usbcore.blinkenlights= 6462 [USB] Set to cycle leds on hubs (default 0 = off). 6463 6464 usbcore.old_scheme_first= 6465 [USB] Start with the old device initialization 6466 scheme (default 0 = off). 6467 6468 usbcore.usbfs_memory_mb= 6469 [USB] Memory limit (in MB) for buffers allocated by 6470 usbfs (default = 16, 0 = max = 2047). 6471 6472 usbcore.use_both_schemes= 6473 [USB] Try the other device initialization scheme 6474 if the first one fails (default 1 = enabled). 6475 6476 usbcore.initial_descriptor_timeout= 6477 [USB] Specifies timeout for the initial 64-byte 6478 USB_REQ_GET_DESCRIPTOR request in milliseconds 6479 (default 5000 = 5.0 seconds). 6480 6481 usbcore.nousb [USB] Disable the USB subsystem 6482 6483 usbcore.quirks= 6484 [USB] A list of quirk entries to augment the built-in 6485 usb core quirk list. List entries are separated by 6486 commas. Each entry has the form 6487 VendorID:ProductID:Flags. The IDs are 4-digit hex 6488 numbers and Flags is a set of letters. Each letter 6489 will change the built-in quirk; setting it if it is 6490 clear and clearing it if it is set. The letters have 6491 the following meanings: 6492 a = USB_QUIRK_STRING_FETCH_255 (string 6493 descriptors must not be fetched using 6494 a 255-byte read); 6495 b = USB_QUIRK_RESET_RESUME (device can't resume 6496 correctly so reset it instead); 6497 c = USB_QUIRK_NO_SET_INTF (device can't handle 6498 Set-Interface requests); 6499 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 6500 handle its Configuration or Interface 6501 strings); 6502 e = USB_QUIRK_RESET (device can't be reset 6503 (e.g morph devices), don't use reset); 6504 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 6505 more interface descriptions than the 6506 bNumInterfaces count, and can't handle 6507 talking to these interfaces); 6508 g = USB_QUIRK_DELAY_INIT (device needs a pause 6509 during initialization, after we read 6510 the device descriptor); 6511 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 6512 high speed and super speed interrupt 6513 endpoints, the USB 2.0 and USB 3.0 spec 6514 require the interval in microframes (1 6515 microframe = 125 microseconds) to be 6516 calculated as interval = 2 ^ 6517 (bInterval-1). 6518 Devices with this quirk report their 6519 bInterval as the result of this 6520 calculation instead of the exponent 6521 variable used in the calculation); 6522 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 6523 handle device_qualifier descriptor 6524 requests); 6525 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 6526 generates spurious wakeup, ignore 6527 remote wakeup capability); 6528 k = USB_QUIRK_NO_LPM (device can't handle Link 6529 Power Management); 6530 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 6531 (Device reports its bInterval as linear 6532 frames instead of the USB 2.0 6533 calculation); 6534 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 6535 to be disconnected before suspend to 6536 prevent spurious wakeup); 6537 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 6538 pause after every control message); 6539 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 6540 delay after resetting its port); 6541 Example: quirks=0781:5580:bk,0a5c:5834:gij 6542 6543 usbhid.mousepoll= 6544 [USBHID] The interval which mice are to be polled at. 6545 6546 usbhid.jspoll= 6547 [USBHID] The interval which joysticks are to be polled at. 6548 6549 usbhid.kbpoll= 6550 [USBHID] The interval which keyboards are to be polled at. 6551 6552 usb-storage.delay_use= 6553 [UMS] The delay in seconds before a new device is 6554 scanned for Logical Units (default 1). 6555 6556 usb-storage.quirks= 6557 [UMS] A list of quirks entries to supplement or 6558 override the built-in unusual_devs list. List 6559 entries are separated by commas. Each entry has 6560 the form VID:PID:Flags where VID and PID are Vendor 6561 and Product ID values (4-digit hex numbers) and 6562 Flags is a set of characters, each corresponding 6563 to a common usb-storage quirk flag as follows: 6564 a = SANE_SENSE (collect more than 18 bytes 6565 of sense data, not on uas); 6566 b = BAD_SENSE (don't collect more than 18 6567 bytes of sense data, not on uas); 6568 c = FIX_CAPACITY (decrease the reported 6569 device capacity by one sector); 6570 d = NO_READ_DISC_INFO (don't use 6571 READ_DISC_INFO command, not on uas); 6572 e = NO_READ_CAPACITY_16 (don't use 6573 READ_CAPACITY_16 command); 6574 f = NO_REPORT_OPCODES (don't use report opcodes 6575 command, uas only); 6576 g = MAX_SECTORS_240 (don't transfer more than 6577 240 sectors at a time, uas only); 6578 h = CAPACITY_HEURISTICS (decrease the 6579 reported device capacity by one 6580 sector if the number is odd); 6581 i = IGNORE_DEVICE (don't bind to this 6582 device); 6583 j = NO_REPORT_LUNS (don't use report luns 6584 command, uas only); 6585 k = NO_SAME (do not use WRITE_SAME, uas only) 6586 l = NOT_LOCKABLE (don't try to lock and 6587 unlock ejectable media, not on uas); 6588 m = MAX_SECTORS_64 (don't transfer more 6589 than 64 sectors = 32 KB at a time, 6590 not on uas); 6591 n = INITIAL_READ10 (force a retry of the 6592 initial READ(10) command, not on uas); 6593 o = CAPACITY_OK (accept the capacity 6594 reported by the device, not on uas); 6595 p = WRITE_CACHE (the device cache is ON 6596 by default, not on uas); 6597 r = IGNORE_RESIDUE (the device reports 6598 bogus residue values, not on uas); 6599 s = SINGLE_LUN (the device has only one 6600 Logical Unit); 6601 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 6602 commands, uas only); 6603 u = IGNORE_UAS (don't bind to the uas driver); 6604 w = NO_WP_DETECT (don't test whether the 6605 medium is write-protected). 6606 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 6607 even if the device claims no cache, 6608 not on uas) 6609 Example: quirks=0419:aaf5:rl,0421:0433:rc 6610 6611 user_debug= [KNL,ARM] 6612 Format: <int> 6613 See arch/arm/Kconfig.debug help text. 6614 1 - undefined instruction events 6615 2 - system calls 6616 4 - invalid data aborts 6617 8 - SIGSEGV faults 6618 16 - SIGBUS faults 6619 Example: user_debug=31 6620 6621 userpte= 6622 [X86] Flags controlling user PTE allocations. 6623 6624 nohigh = do not allocate PTE pages in 6625 HIGHMEM regardless of setting 6626 of CONFIG_HIGHPTE. 6627 6628 vdso= [X86,SH,SPARC] 6629 On X86_32, this is an alias for vdso32=. Otherwise: 6630 6631 vdso=1: enable VDSO (the default) 6632 vdso=0: disable VDSO mapping 6633 6634 vdso32= [X86] Control the 32-bit vDSO 6635 vdso32=1: enable 32-bit VDSO 6636 vdso32=0 or vdso32=2: disable 32-bit VDSO 6637 6638 See the help text for CONFIG_COMPAT_VDSO for more 6639 details. If CONFIG_COMPAT_VDSO is set, the default is 6640 vdso32=0; otherwise, the default is vdso32=1. 6641 6642 For compatibility with older kernels, vdso32=2 is an 6643 alias for vdso32=0. 6644 6645 Try vdso32=0 if you encounter an error that says: 6646 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 6647 6648 vector= [IA-64,SMP] 6649 vector=percpu: enable percpu vector domain 6650 6651 video= [FB] Frame buffer configuration 6652 See Documentation/fb/modedb.rst. 6653 6654 video.brightness_switch_enabled= [ACPI] 6655 Format: [0|1] 6656 If set to 1, on receiving an ACPI notify event 6657 generated by hotkey, video driver will adjust brightness 6658 level and then send out the event to user space through 6659 the allocated input device. If set to 0, video driver 6660 will only send out the event without touching backlight 6661 brightness level. 6662 default: 1 6663 6664 virtio_mmio.device= 6665 [VMMIO] Memory mapped virtio (platform) device. 6666 6667 <size>@<baseaddr>:<irq>[:<id>] 6668 where: 6669 <size> := size (can use standard suffixes 6670 like K, M and G) 6671 <baseaddr> := physical base address 6672 <irq> := interrupt number (as passed to 6673 request_irq()) 6674 <id> := (optional) platform device id 6675 example: 6676 virtio_mmio.device=1K@0x100b0000:48:7 6677 6678 Can be used multiple times for multiple devices. 6679 6680 vga= [BOOT,X86-32] Select a particular video mode 6681 See Documentation/x86/boot.rst and 6682 Documentation/admin-guide/svga.rst. 6683 Use vga=ask for menu. 6684 This is actually a boot loader parameter; the value is 6685 passed to the kernel using a special protocol. 6686 6687 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 6688 May slow down system boot speed, especially when 6689 enabled on systems with a large amount of memory. 6690 All options are enabled by default, and this 6691 interface is meant to allow for selectively 6692 enabling or disabling specific virtual memory 6693 debugging features. 6694 6695 Available options are: 6696 P Enable page structure init time poisoning 6697 - Disable all of the above options 6698 6699 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 6700 size of <nn>. This can be used to increase the 6701 minimum size (128MB on x86). It can also be used to 6702 decrease the size and leave more room for directly 6703 mapped kernel RAM. 6704 6705 vmcp_cma=nn[MG] [KNL,S390] 6706 Sets the memory size reserved for contiguous memory 6707 allocations for the vmcp device driver. 6708 6709 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 6710 Format: <command> 6711 6712 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 6713 Format: <command> 6714 6715 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 6716 Format: <command> 6717 6718 vsyscall= [X86-64] 6719 Controls the behavior of vsyscalls (i.e. calls to 6720 fixed addresses of 0xffffffffff600x00 from legacy 6721 code). Most statically-linked binaries and older 6722 versions of glibc use these calls. Because these 6723 functions are at fixed addresses, they make nice 6724 targets for exploits that can control RIP. 6725 6726 emulate [default] Vsyscalls turn into traps and are 6727 emulated reasonably safely. The vsyscall 6728 page is readable. 6729 6730 xonly Vsyscalls turn into traps and are 6731 emulated reasonably safely. The vsyscall 6732 page is not readable. 6733 6734 none Vsyscalls don't work at all. This makes 6735 them quite hard to use for exploits but 6736 might break your system. 6737 6738 vt.color= [VT] Default text color. 6739 Format: 0xYX, X = foreground, Y = background. 6740 Default: 0x07 = light gray on black. 6741 6742 vt.cur_default= [VT] Default cursor shape. 6743 Format: 0xCCBBAA, where AA, BB, and CC are the same as 6744 the parameters of the <Esc>[?A;B;Cc escape sequence; 6745 see VGA-softcursor.txt. Default: 2 = underline. 6746 6747 vt.default_blu= [VT] 6748 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 6749 Change the default blue palette of the console. 6750 This is a 16-member array composed of values 6751 ranging from 0-255. 6752 6753 vt.default_grn= [VT] 6754 Format: <green0>,<green1>,<green2>,...,<green15> 6755 Change the default green palette of the console. 6756 This is a 16-member array composed of values 6757 ranging from 0-255. 6758 6759 vt.default_red= [VT] 6760 Format: <red0>,<red1>,<red2>,...,<red15> 6761 Change the default red palette of the console. 6762 This is a 16-member array composed of values 6763 ranging from 0-255. 6764 6765 vt.default_utf8= 6766 [VT] 6767 Format=<0|1> 6768 Set system-wide default UTF-8 mode for all tty's. 6769 Default is 1, i.e. UTF-8 mode is enabled for all 6770 newly opened terminals. 6771 6772 vt.global_cursor_default= 6773 [VT] 6774 Format=<-1|0|1> 6775 Set system-wide default for whether a cursor 6776 is shown on new VTs. Default is -1, 6777 i.e. cursors will be created by default unless 6778 overridden by individual drivers. 0 will hide 6779 cursors, 1 will display them. 6780 6781 vt.italic= [VT] Default color for italic text; 0-15. 6782 Default: 2 = green. 6783 6784 vt.underline= [VT] Default color for underlined text; 0-15. 6785 Default: 3 = cyan. 6786 6787 watchdog timers [HW,WDT] For information on watchdog timers, 6788 see Documentation/watchdog/watchdog-parameters.rst 6789 or other driver-specific files in the 6790 Documentation/watchdog/ directory. 6791 6792 watchdog_thresh= 6793 [KNL] 6794 Set the hard lockup detector stall duration 6795 threshold in seconds. The soft lockup detector 6796 threshold is set to twice the value. A value of 0 6797 disables both lockup detectors. Default is 10 6798 seconds. 6799 6800 workqueue.watchdog_thresh= 6801 If CONFIG_WQ_WATCHDOG is configured, workqueue can 6802 warn stall conditions and dump internal state to 6803 help debugging. 0 disables workqueue stall 6804 detection; otherwise, it's the stall threshold 6805 duration in seconds. The default value is 30 and 6806 it can be updated at runtime by writing to the 6807 corresponding sysfs file. 6808 6809 workqueue.disable_numa 6810 By default, all work items queued to unbound 6811 workqueues are affine to the NUMA nodes they're 6812 issued on, which results in better behavior in 6813 general. If NUMA affinity needs to be disabled for 6814 whatever reason, this option can be used. Note 6815 that this also can be controlled per-workqueue for 6816 workqueues visible under /sys/bus/workqueue/. 6817 6818 workqueue.power_efficient 6819 Per-cpu workqueues are generally preferred because 6820 they show better performance thanks to cache 6821 locality; unfortunately, per-cpu workqueues tend to 6822 be more power hungry than unbound workqueues. 6823 6824 Enabling this makes the per-cpu workqueues which 6825 were observed to contribute significantly to power 6826 consumption unbound, leading to measurably lower 6827 power usage at the cost of small performance 6828 overhead. 6829 6830 The default value of this parameter is determined by 6831 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 6832 6833 workqueue.debug_force_rr_cpu 6834 Workqueue used to implicitly guarantee that work 6835 items queued without explicit CPU specified are put 6836 on the local CPU. This guarantee is no longer true 6837 and while local CPU is still preferred work items 6838 may be put on foreign CPUs. This debug option 6839 forces round-robin CPU selection to flush out 6840 usages which depend on the now broken guarantee. 6841 When enabled, memory and cache locality will be 6842 impacted. 6843 6844 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 6845 default x2apic cluster mode on platforms 6846 supporting x2apic. 6847 6848 xen_512gb_limit [KNL,X86-64,XEN] 6849 Restricts the kernel running paravirtualized under Xen 6850 to use only up to 512 GB of RAM. The reason to do so is 6851 crash analysis tools and Xen tools for doing domain 6852 save/restore/migration must be enabled to handle larger 6853 domains. 6854 6855 xen_emul_unplug= [HW,X86,XEN] 6856 Unplug Xen emulated devices 6857 Format: [unplug0,][unplug1] 6858 ide-disks -- unplug primary master IDE devices 6859 aux-ide-disks -- unplug non-primary-master IDE devices 6860 nics -- unplug network devices 6861 all -- unplug all emulated devices (NICs and IDE disks) 6862 unnecessary -- unplugging emulated devices is 6863 unnecessary even if the host did not respond to 6864 the unplug protocol 6865 never -- do not unplug even if version check succeeds 6866 6867 xen_legacy_crash [X86,XEN] 6868 Crash from Xen panic notifier, without executing late 6869 panic() code such as dumping handler. 6870 6871 xen_msr_safe= [X86,XEN] 6872 Format: <bool> 6873 Select whether to always use non-faulting (safe) MSR 6874 access functions when running as Xen PV guest. The 6875 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 6876 6877 xen_nopvspin [X86,XEN] 6878 Disables the qspinlock slowpath using Xen PV optimizations. 6879 This parameter is obsoleted by "nopvspin" parameter, which 6880 has equivalent effect for XEN platform. 6881 6882 xen_nopv [X86] 6883 Disables the PV optimizations forcing the HVM guest to 6884 run as generic HVM guest with no PV drivers. 6885 This option is obsoleted by the "nopv" option, which 6886 has equivalent effect for XEN platform. 6887 6888 xen_no_vector_callback 6889 [KNL,X86,XEN] Disable the vector callback for Xen 6890 event channel interrupts. 6891 6892 xen_scrub_pages= [XEN] 6893 Boolean option to control scrubbing pages before giving them back 6894 to Xen, for use by other domains. Can be also changed at runtime 6895 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 6896 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 6897 6898 xen_timer_slop= [X86-64,XEN] 6899 Set the timer slop (in nanoseconds) for the virtual Xen 6900 timers (default is 100000). This adjusts the minimum 6901 delta of virtualized Xen timers, where lower values 6902 improve timer resolution at the expense of processing 6903 more timer interrupts. 6904 6905 xen.balloon_boot_timeout= [XEN] 6906 The time (in seconds) to wait before giving up to boot 6907 in case initial ballooning fails to free enough memory. 6908 Applies only when running as HVM or PVH guest and 6909 started with less memory configured than allowed at 6910 max. Default is 180. 6911 6912 xen.event_eoi_delay= [XEN] 6913 How long to delay EOI handling in case of event 6914 storms (jiffies). Default is 10. 6915 6916 xen.event_loop_timeout= [XEN] 6917 After which time (jiffies) the event handling loop 6918 should start to delay EOI handling. Default is 2. 6919 6920 xen.fifo_events= [XEN] 6921 Boolean parameter to disable using fifo event handling 6922 even if available. Normally fifo event handling is 6923 preferred over the 2-level event handling, as it is 6924 fairer and the number of possible event channels is 6925 much higher. Default is on (use fifo events). 6926 6927 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 6928 Disables the PV optimizations forcing the guest to run 6929 as generic guest with no PV drivers. Currently support 6930 XEN HVM, KVM, HYPER_V and VMWARE guest. 6931 6932 nopvspin [X86,XEN,KVM] 6933 Disables the qspinlock slow path using PV optimizations 6934 which allow the hypervisor to 'idle' the guest on lock 6935 contention. 6936 6937 xirc2ps_cs= [NET,PCMCIA] 6938 Format: 6939 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 6940 6941 xive= [PPC] 6942 By default on POWER9 and above, the kernel will 6943 natively use the XIVE interrupt controller. This option 6944 allows the fallback firmware mode to be used: 6945 6946 off Fallback to firmware control of XIVE interrupt 6947 controller on both pseries and powernv 6948 platforms. Only useful on POWER9 and above. 6949 6950 xive.store-eoi=off [PPC] 6951 By default on POWER10 and above, the kernel will use 6952 stores for EOI handling when the XIVE interrupt mode 6953 is active. This option allows the XIVE driver to use 6954 loads instead, as on POWER9. 6955 6956 xhci-hcd.quirks [USB,KNL] 6957 A hex value specifying bitmask with supplemental xhci 6958 host controller quirks. Meaning of each bit can be 6959 consulted in header drivers/usb/host/xhci.h. 6960 6961 xmon [PPC] 6962 Format: { early | on | rw | ro | off } 6963 Controls if xmon debugger is enabled. Default is off. 6964 Passing only "xmon" is equivalent to "xmon=early". 6965 early Call xmon as early as possible on boot; xmon 6966 debugger is called from setup_arch(). 6967 on xmon debugger hooks will be installed so xmon 6968 is only called on a kernel crash. Default mode, 6969 i.e. either "ro" or "rw" mode, is controlled 6970 with CONFIG_XMON_DEFAULT_RO_MODE. 6971 rw xmon debugger hooks will be installed so xmon 6972 is called only on a kernel crash, mode is write, 6973 meaning SPR registers, memory and, other data 6974 can be written using xmon commands. 6975 ro same as "rw" option above but SPR registers, 6976 memory, and other data can't be written using 6977 xmon commands. 6978 off xmon is disabled. 6979 6980 amd_pstate= [X86] 6981 disable 6982 Do not enable amd_pstate as the default 6983 scaling driver for the supported processors 6984 passive 6985 Use amd_pstate as a scaling driver, driver requests a 6986 desired performance on this abstract scale and the power 6987 management firmware translates the requests into actual 6988 hardware states (core frequency, data fabric and memory 6989 clocks etc.) 6990