1 /* vi: set sw=4 ts=4: */
2 /*
3 * Mini init implementation for busybox
4 *
5 * Copyright (C) 1995, 1996 by Bruce Perens <bruce@pixar.com>.
6 * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
7 * Adjusted by so many folks, it's impossible to keep track.
8 *
9 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
10 */
11 //config:config INIT
12 //config: bool "init (10 kb)"
13 //config: default y
14 //config: select FEATURE_SYSLOG
15 //config: help
16 //config: init is the first program run when the system boots.
17 //config:
18 //config:config LINUXRC
19 //config: bool "linuxrc: support running init from initrd (not initramfs)"
20 //config: default y
21 //config: select FEATURE_SYSLOG
22 //config: help
23 //config: Legacy support for running init under the old-style initrd. Allows
24 //config: the name linuxrc to act as init, and it doesn't assume init is PID 1.
25 //config:
26 //config: This does not apply to initramfs, which runs /init as PID 1 and
27 //config: requires no special support.
28 //config:
29 //config:config FEATURE_USE_INITTAB
30 //config: bool "Support reading an inittab file"
31 //config: default y
32 //config: depends on INIT || LINUXRC
33 //config: help
34 //config: Allow init to read an inittab file when the system boot.
35 //config:
36 //config:config FEATURE_KILL_REMOVED
37 //config: bool "Support killing processes that have been removed from inittab"
38 //config: default n
39 //config: depends on FEATURE_USE_INITTAB
40 //config: help
41 //config: When respawn entries are removed from inittab and a SIGHUP is
42 //config: sent to init, this option will make init kill the processes
43 //config: that have been removed.
44 //config:
45 //config:config FEATURE_KILL_DELAY
46 //config: int "How long to wait between TERM and KILL (0 - send TERM only)" if FEATURE_KILL_REMOVED
47 //config: range 0 1024
48 //config: default 0
49 //config: depends on FEATURE_KILL_REMOVED
50 //config: help
51 //config: With nonzero setting, init sends TERM, forks, child waits N
52 //config: seconds, sends KILL and exits. Setting it too high is unwise
53 //config: (child will hang around for too long and could actually kill
54 //config: the wrong process!)
55 //config:
56 //config:config FEATURE_INIT_SCTTY
57 //config: bool "Run commands with leading dash with controlling tty"
58 //config: default y
59 //config: depends on INIT || LINUXRC
60 //config: help
61 //config: If this option is enabled, init will try to give a controlling
62 //config: tty to any command which has leading hyphen (often it's "-/bin/sh").
63 //config: More precisely, init will do "ioctl(STDIN_FILENO, TIOCSCTTY, 0)".
64 //config: If device attached to STDIN_FILENO can be a ctty but is not yet
65 //config: a ctty for other session, it will become this process' ctty.
66 //config: This is not the traditional init behavour, but is often what you want
67 //config: in an embedded system where the console is only accessed during
68 //config: development or for maintenance.
69 //config: NB: using cttyhack applet may work better.
70 //config:
71 //config:config FEATURE_INIT_SYSLOG
72 //config: bool "Enable init to write to syslog"
73 //config: default y
74 //config: depends on INIT || LINUXRC
75 //config: help
76 //config: If selected, some init messages are sent to syslog.
77 //config: Otherwise, they are sent to VT #5 if linux virtual tty is detected
78 //config: (if not, no separate logging is done).
79 //config:
80 //config:config FEATURE_INIT_QUIET
81 //config: bool "Be quiet on boot (no 'init started:' message)"
82 //config: default y
83 //config: depends on INIT || LINUXRC
84 //config:
85 //config:config FEATURE_INIT_COREDUMPS
86 //config: bool "Support dumping core for child processes (debugging only)"
87 //config: default n # not Y because this is a debug option
88 //config: depends on INIT || LINUXRC
89 //config: help
90 //config: If this option is enabled and the file /.init_enable_core
91 //config: exists, then init will call setrlimit() to allow unlimited
92 //config: core file sizes. If this option is disabled, processes
93 //config: will not generate any core files.
94 //config:
95 //config:config INIT_TERMINAL_TYPE
96 //config: string "Initial terminal type"
97 //config: default "linux"
98 //config: depends on INIT || LINUXRC
99 //config: help
100 //config: This is the initial value set by init for the TERM environment
101 //config: variable. This variable is used by programs which make use of
102 //config: extended terminal capabilities.
103 //config:
104 //config: Note that on Linux, init attempts to detect serial terminal and
105 //config: sets TERM to "vt102" if one is found.
106 //config:
107 //config:config FEATURE_INIT_MODIFY_CMDLINE
108 //config: bool "Clear init's command line"
109 //config: default y
110 //config: depends on INIT || LINUXRC
111 //config: help
112 //config: When launched as PID 1 and after parsing its arguments, init
113 //config: wipes all the arguments but argv[0] and rewrites argv[0] to
114 //config: contain only "init", so that its command line appears solely as
115 //config: "init" in tools such as ps.
116 //config: If this option is set to Y, init will keep its original behavior,
117 //config: otherwise, all the arguments including argv[0] will be preserved,
118 //config: be they parsed or ignored by init.
119 //config: The original command-line used to launch init can then be
120 //config: retrieved in /proc/1/cmdline on Linux, for example.
121
122 //applet:IF_INIT(APPLET(init, BB_DIR_SBIN, BB_SUID_DROP))
123 //applet:IF_LINUXRC(APPLET_ODDNAME(linuxrc, init, BB_DIR_ROOT, BB_SUID_DROP, linuxrc))
124
125 //kbuild:lib-$(CONFIG_INIT) += init.o
126 //kbuild:lib-$(CONFIG_LINUXRC) += init.o
127
128 #define DEBUG_SEGV_HANDLER 0
129
130 #include "libbb.h"
131 #include "common_bufsiz.h"
132 #include <syslog.h>
133 #ifdef __linux__
134 # include <linux/vt.h>
135 # include <sys/sysinfo.h>
136 #endif
137 #include "reboot.h" /* reboot() constants */
138
139 #if DEBUG_SEGV_HANDLER
140 # undef _GNU_SOURCE
141 # define _GNU_SOURCE 1
142 # undef __USE_GNU
143 # define __USE_GNU 1
144 # include <execinfo.h>
145 # include <sys/ucontext.h>
146 #endif
147
148 /* Was a CONFIG_xxx option. A lot of people were building
149 * not fully functional init by switching it on! */
150 #define DEBUG_INIT 0
151
152 #define CONSOLE_NAME_SIZE 32
153
154 /* Default sysinit script. */
155 #ifndef INIT_SCRIPT
156 # define INIT_SCRIPT "/etc/init.d/rcS"
157 #endif
158
159 /* Each type of actions can appear many times. They will be
160 * handled in order. RESTART is an exception, only 1st is used.
161 */
162 /* Start these actions first and wait for completion */
163 #define SYSINIT 0x01
164 /* Start these after SYSINIT and wait for completion */
165 #define WAIT 0x02
166 /* Start these after WAIT and *dont* wait for completion */
167 #define ONCE 0x04
168 /*
169 * NB: while SYSINIT/WAIT/ONCE are being processed,
170 * SIGHUP ("reread /etc/inittab") will be processed only after
171 * each group of actions. If new inittab adds, say, a SYSINIT action,
172 * it will not be run, since init is already "past SYSINIT stage".
173 */
174 /* Start these after ONCE are started, restart on exit */
175 #define RESPAWN 0x08
176 /* Like RESPAWN, but wait for <Enter> to be pressed on tty */
177 #define ASKFIRST 0x10
178 /*
179 * Start these on SIGINT, and wait for completion.
180 * Then go back to respawning RESPAWN and ASKFIRST actions.
181 * NB: kernel sends SIGINT to us if Ctrl-Alt-Del was pressed.
182 */
183 #define CTRLALTDEL 0x20
184 /*
185 * Start these before killing all processes in preparation for
186 * running RESTART actions or doing low-level halt/reboot/poweroff
187 * (initiated by SIGUSR1/SIGTERM/SIGUSR2).
188 * Wait for completion before proceeding.
189 */
190 #define SHUTDOWN 0x40
191 /*
192 * exec() on SIGQUIT. SHUTDOWN actions are started and waited for,
193 * then all processes are killed, then init exec's 1st RESTART action,
194 * replacing itself by it. If no RESTART action specified,
195 * SIGQUIT has no effect.
196 */
197 #define RESTART 0x80
198
199 /* A linked list of init_actions, to be read from inittab */
200 struct init_action {
201 struct init_action *next;
202 pid_t pid;
203 uint8_t action_type;
204 char terminal[CONSOLE_NAME_SIZE];
205 char command[1];
206 };
207
208 struct globals {
209 struct init_action *init_action_list;
210 #if !ENABLE_FEATURE_INIT_SYSLOG
211 const char *log_console;
212 #endif
213 sigset_t delayed_sigset;
214 struct timespec zero_ts;
215 } FIX_ALIASING;
216 #define G (*(struct globals*)bb_common_bufsiz1)
217 #define INIT_G() do { \
218 setup_common_bufsiz(); \
219 IF_NOT_FEATURE_INIT_SYSLOG(G.log_console = VC_5;) \
220 } while (0)
221
222 enum {
223 L_LOG = 0x1,
224 L_CONSOLE = 0x2,
225 };
226
227 /* Print a message to the specified device.
228 * "where" may be bitwise-or'd from L_LOG | L_CONSOLE
229 * NB: careful, we can be called after vfork!
230 */
231 #define dbg_message(...) do { if (DEBUG_INIT) message(__VA_ARGS__); } while (0)
232 static void message(int where, const char *fmt, ...)
233 __attribute__ ((format(printf, 2, 3)));
message(int where,const char * fmt,...)234 static void message(int where, const char *fmt, ...)
235 {
236 va_list arguments;
237 unsigned l;
238 char msg[128];
239
240 msg[0] = '\r';
241 va_start(arguments, fmt);
242 l = 1 + vsnprintf(msg + 1, sizeof(msg) - 2, fmt, arguments);
243 if (l > sizeof(msg) - 2)
244 l = sizeof(msg) - 2;
245 va_end(arguments);
246
247 #if ENABLE_FEATURE_INIT_SYSLOG
248 msg[l] = '\0';
249 if (where & L_LOG) {
250 /* Log the message to syslogd */
251 openlog(applet_name, 0, LOG_DAEMON);
252 /* don't print "\r" */
253 syslog(LOG_INFO, "%s", msg + 1);
254 closelog();
255 }
256 msg[l++] = '\n';
257 msg[l] = '\0';
258 #else
259 msg[l++] = '\n';
260 msg[l] = '\0';
261 if (where & L_LOG) {
262 /* Take full control of the log tty, and never close it.
263 * It's mine, all mine! Muhahahaha! */
264 static int log_fd = -1;
265
266 if (log_fd < 0) {
267 log_fd = STDERR_FILENO;
268 if (G.log_console) {
269 log_fd = device_open(G.log_console, O_WRONLY | O_NONBLOCK | O_NOCTTY);
270 if (log_fd < 0) {
271 bb_error_msg("can't log to %s", G.log_console);
272 where = L_CONSOLE;
273 } else {
274 close_on_exec_on(log_fd);
275 }
276 }
277 }
278 full_write(log_fd, msg, l);
279 if (log_fd == STDERR_FILENO)
280 return; /* don't print dup messages */
281 }
282 #endif
283
284 if (where & L_CONSOLE) {
285 /* Send console messages to console so people will see them. */
286 full_write(STDERR_FILENO, msg, l);
287 }
288 }
289
console_init(void)290 static void console_init(void)
291 {
292 #ifdef VT_OPENQRY
293 int vtno;
294 #endif
295 char *s;
296
297 s = getenv("CONSOLE");
298 if (!s)
299 s = getenv("console");
300 #if defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
301 /* BSD people say their kernels do not open fd 0,1,2; they need this: */
302 if (!s)
303 s = (char*)"/dev/console";
304 #endif
305 if (s) {
306 int fd = open(s, O_RDWR | O_NONBLOCK | O_NOCTTY);
307 if (fd >= 0) {
308 dup2(fd, STDIN_FILENO);
309 dup2(fd, STDOUT_FILENO);
310 xmove_fd(fd, STDERR_FILENO);
311 }
312 dbg_message(L_LOG, "console='%s'", s);
313 } else {
314 /* Make sure fd 0,1,2 are not closed
315 * (so that they won't be used by future opens) */
316 bb_sanitize_stdio();
317 // Users report problems
318 // /* Make sure init can't be blocked by writing to stderr */
319 // fcntl(STDERR_FILENO, F_SETFL, fcntl(STDERR_FILENO, F_GETFL) | O_NONBLOCK);
320 }
321
322 s = getenv("TERM");
323 #ifdef VT_OPENQRY
324 if (ioctl(STDIN_FILENO, VT_OPENQRY, &vtno) != 0) {
325 /* Not a linux terminal, probably serial console.
326 * Force the TERM setting to vt102
327 * if TERM is set to linux (the default) */
328 if (!s || strcmp(s, "linux") == 0)
329 putenv((char*)"TERM=vt102");
330 # if !ENABLE_FEATURE_INIT_SYSLOG
331 G.log_console = NULL;
332 # endif
333 } else
334 #endif
335 if (!s)
336 putenv((char*)"TERM=" CONFIG_INIT_TERMINAL_TYPE);
337 }
338
339 /* Set terminal settings to reasonable defaults.
340 * NB: careful, we can be called after vfork! */
set_sane_term(void)341 static void set_sane_term(void)
342 {
343 struct termios tty;
344
345 if (tcgetattr(STDIN_FILENO, &tty) != 0)
346 return;
347
348 /* set control chars */
349 tty.c_cc[VINTR] = 3; /* C-c */
350 tty.c_cc[VQUIT] = 28; /* C-\ */
351 tty.c_cc[VERASE] = 127; /* C-? */
352 tty.c_cc[VKILL] = 21; /* C-u */
353 tty.c_cc[VEOF] = 4; /* C-d */
354 tty.c_cc[VSTART] = 17; /* C-q */
355 tty.c_cc[VSTOP] = 19; /* C-s */
356 tty.c_cc[VSUSP] = 26; /* C-z */
357
358 #ifdef __linux__
359 /* use line discipline 0 */
360 tty.c_line = 0;
361 #endif
362
363 /* Make it be sane */
364 /* On systems where the baud rate is stored in a separate field, we can safely disable these. */
365 #ifndef CBAUD
366 # define CBAUD 0
367 # define CBAUDEX 0
368 #endif
369 /* Added CRTSCTS to fix Debian bug 528560 */
370 #ifndef CRTSCTS
371 # define CRTSCTS 0
372 #endif
373 tty.c_cflag &= CBAUD | CBAUDEX | CSIZE | CSTOPB | PARENB | PARODD | CRTSCTS;
374 tty.c_cflag |= CREAD | HUPCL | CLOCAL;
375
376 /* input modes */
377 tty.c_iflag = ICRNL | IXON | IXOFF;
378
379 /* output modes */
380 tty.c_oflag = OPOST | ONLCR;
381
382 /* local modes */
383 tty.c_lflag = ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHOCTL | ECHOKE | IEXTEN;
384
385 tcsetattr_stdin_TCSANOW(&tty);
386 }
387
388 /* Open the new terminal device.
389 * NB: careful, we can be called after vfork! */
open_stdio_to_tty(const char * tty_name)390 static int open_stdio_to_tty(const char* tty_name)
391 {
392 /* empty tty_name means "use init's tty", else... */
393 if (tty_name[0]) {
394 int fd;
395
396 close(STDIN_FILENO);
397 /* fd can be only < 0 or 0: */
398 fd = device_open(tty_name, O_RDWR);
399 if (fd) {
400 message(L_LOG | L_CONSOLE, "can't open %s: "STRERROR_FMT,
401 tty_name
402 STRERROR_ERRNO
403 );
404 return 0; /* failure */
405 }
406 dup2(STDIN_FILENO, STDOUT_FILENO);
407 dup2(STDIN_FILENO, STDERR_FILENO);
408 }
409 set_sane_term();
410 return 1; /* success */
411 }
412
reset_sighandlers_and_unblock_sigs(void)413 static void reset_sighandlers_and_unblock_sigs(void)
414 {
415 bb_signals(0
416 | (1 << SIGTSTP)
417 | (1 << SIGSTOP)
418 , SIG_DFL);
419 sigprocmask_allsigs(SIG_UNBLOCK);
420 }
421
422 /* Wrapper around exec:
423 * Takes string.
424 * If chars like '>' detected, execs '[-]/bin/sh -c "exec ......."'.
425 * Otherwise splits words on whitespace, deals with leading dash,
426 * and uses plain exec().
427 * NB: careful, we can be called after vfork!
428 */
init_exec(const char * command)429 static void init_exec(const char *command)
430 {
431 /* +8 allows to write VLA sizes below more efficiently: */
432 unsigned command_size = strlen(command) + 8;
433 /* strlen(command) + strlen("exec ")+1: */
434 char buf[command_size];
435 /* strlen(command) / 2 + 4: */
436 char *cmd[command_size / 2];
437 int dash;
438
439 dash = (command[0] == '-' /* maybe? && command[1] == '/' */);
440 command += dash;
441
442 /* See if any special /bin/sh requiring characters are present */
443 if (strpbrk(command, "~`!$^&*()=|\\{}[];\"'<>?") != NULL) {
444 sprintf(buf, "exec %s", command); /* excluding "-" */
445 /* NB: LIBBB_DEFAULT_LOGIN_SHELL define has leading dash */
446 cmd[0] = (char*)(LIBBB_DEFAULT_LOGIN_SHELL + !dash);
447 cmd[1] = (char*)"-c";
448 cmd[2] = buf;
449 cmd[3] = NULL;
450 command = LIBBB_DEFAULT_LOGIN_SHELL + 1;
451 } else {
452 /* Convert command (char*) into cmd (char**, one word per string) */
453 char *word, *next;
454 int i = 0;
455 next = strcpy(buf, command - dash); /* command including "-" */
456 command = next + dash;
457 while ((word = strsep(&next, " \t")) != NULL) {
458 if (*word != '\0') { /* not two spaces/tabs together? */
459 cmd[i] = word;
460 i++;
461 }
462 }
463 cmd[i] = NULL;
464 }
465 /* If we saw leading "-", it is interactive shell.
466 * Try harder to give it a controlling tty.
467 */
468 if (ENABLE_FEATURE_INIT_SCTTY && dash) {
469 /* _Attempt_ to make stdin a controlling tty. */
470 ioctl(STDIN_FILENO, TIOCSCTTY, 0 /*only try, don't steal*/);
471 }
472 /* Here command never contains the dash, cmd[0] might */
473 BB_EXECVP(command, cmd);
474 message(L_LOG | L_CONSOLE, "can't run '%s': "STRERROR_FMT, command STRERROR_ERRNO);
475 /* returns if execvp fails */
476 }
477
478 /* Used only by run_actions */
run(const struct init_action * a)479 static pid_t run(const struct init_action *a)
480 {
481 pid_t pid;
482
483 if (BB_MMU && (a->action_type & ASKFIRST))
484 pid = fork();
485 else
486 pid = vfork();
487 if (pid) {
488 if (pid < 0)
489 message(L_LOG | L_CONSOLE, "can't fork");
490 return pid; /* Parent or error */
491 }
492
493 /* Child */
494
495 /* Reset signal handlers that were set by the parent process */
496 reset_sighandlers_and_unblock_sigs();
497
498 /* Create a new session and make ourself the process group leader */
499 setsid();
500
501 /* Open the new terminal device */
502 if (!open_stdio_to_tty(a->terminal))
503 _exit(EXIT_FAILURE);
504
505 /* NB: on NOMMU we can't wait for input in child, so
506 * "askfirst" will work the same as "respawn". */
507 if (BB_MMU && (a->action_type & ASKFIRST)) {
508 static const char press_enter[] ALIGN1 =
509 #ifdef CUSTOMIZED_BANNER
510 #include CUSTOMIZED_BANNER
511 #endif
512 "\nPlease press Enter to activate this console. ";
513 char c;
514 /*
515 * Save memory by not exec-ing anything large (like a shell)
516 * before the user wants it. This is critical if swap is not
517 * enabled and the system has low memory. Generally this will
518 * be run on the second virtual console, and the first will
519 * be allowed to start a shell or whatever an init script
520 * specifies.
521 */
522 dbg_message(L_LOG, "waiting for enter to start '%s'"
523 "(pid %d, tty '%s')\n",
524 a->command, getpid(), a->terminal);
525 full_write(STDOUT_FILENO, press_enter, sizeof(press_enter) - 1);
526 while (safe_read(STDIN_FILENO, &c, 1) == 1 && c != '\n')
527 continue;
528 }
529
530 /*
531 * When a file named /.init_enable_core exists, setrlimit is called
532 * before processes are spawned to set core file size as unlimited.
533 * This is for debugging only. Don't use this is production, unless
534 * you want core dumps lying about....
535 */
536 if (ENABLE_FEATURE_INIT_COREDUMPS) {
537 if (access("/.init_enable_core", F_OK) == 0) {
538 struct rlimit limit;
539 limit.rlim_cur = RLIM_INFINITY;
540 limit.rlim_max = RLIM_INFINITY;
541 setrlimit(RLIMIT_CORE, &limit);
542 }
543 }
544
545 /* Log the process name and args */
546 message(L_LOG, "starting pid %u, tty '%s': '%s'",
547 (int)getpid(), a->terminal, a->command);
548
549 /* Now run it. The new program will take over this PID,
550 * so nothing further in init.c should be run. */
551 init_exec(a->command);
552 /* We're still here? Some error happened. */
553 _exit(-1);
554 }
555
mark_terminated(pid_t pid)556 static struct init_action *mark_terminated(pid_t pid)
557 {
558 struct init_action *a;
559
560 if (pid > 0) {
561 update_utmp_DEAD_PROCESS(pid);
562 for (a = G.init_action_list; a; a = a->next) {
563 if (a->pid == pid) {
564 a->pid = 0;
565 return a;
566 }
567 }
568 }
569 return NULL;
570 }
571
waitfor(pid_t pid)572 static void waitfor(pid_t pid)
573 {
574 /* waitfor(run(x)): protect against failed fork inside run() */
575 if (pid <= 0)
576 return;
577
578 /* Wait for any child (prevent zombies from exiting orphaned processes)
579 * but exit the loop only when specified one has exited. */
580 while (1) {
581 pid_t wpid = wait(NULL);
582 mark_terminated(wpid);
583 if (wpid == pid) /* this was the process we waited for */
584 break;
585 /* The above is not reliable enough: SIGTSTP handler might have
586 * wait'ed it already. Double check, exit if process is gone:
587 */
588 if (kill(pid, 0))
589 break;
590 }
591 }
592
593 /* Run all commands of a particular type */
run_actions(int action_type)594 static void run_actions(int action_type)
595 {
596 struct init_action *a;
597
598 for (a = G.init_action_list; a; a = a->next) {
599 if (!(a->action_type & action_type))
600 continue;
601
602 if (a->action_type & (SYSINIT | WAIT | ONCE | CTRLALTDEL | SHUTDOWN)) {
603 pid_t pid = run(a);
604 if (a->action_type & (SYSINIT | WAIT | CTRLALTDEL | SHUTDOWN))
605 waitfor(pid);
606 }
607 if (a->action_type & (RESPAWN | ASKFIRST)) {
608 /* Only run stuff with pid == 0. If pid != 0,
609 * it is already running
610 */
611 if (a->pid == 0)
612 a->pid = run(a);
613 }
614 }
615 }
616
new_init_action(uint8_t action_type,const char * command,const char * cons)617 static void new_init_action(uint8_t action_type, const char *command, const char *cons)
618 {
619 struct init_action *a, **nextp;
620
621 /* Scenario:
622 * old inittab:
623 * ::shutdown:umount -a -r
624 * ::shutdown:swapoff -a
625 * new inittab:
626 * ::shutdown:swapoff -a
627 * ::shutdown:umount -a -r
628 * On reload, we must ensure entries end up in correct order.
629 * To achieve that, if we find a matching entry, we move it
630 * to the end.
631 */
632 nextp = &G.init_action_list;
633 while ((a = *nextp) != NULL) {
634 /* Don't enter action if it's already in the list.
635 * This prevents losing running RESPAWNs.
636 */
637 if (strcmp(a->command, command) == 0
638 && strcmp(a->terminal, cons) == 0
639 ) {
640 /* Remove from list */
641 *nextp = a->next;
642 /* Find the end of the list */
643 while (*nextp != NULL)
644 nextp = &(*nextp)->next;
645 a->next = NULL;
646 goto append;
647 }
648 nextp = &a->next;
649 }
650
651 a = xzalloc(sizeof(*a) + strlen(command));
652
653 /* Append to the end of the list */
654 append:
655 *nextp = a;
656 a->action_type = action_type;
657 strcpy(a->command, command);
658 safe_strncpy(a->terminal, cons, sizeof(a->terminal));
659 dbg_message(L_LOG | L_CONSOLE, "command='%s' action=%x tty='%s'\n",
660 a->command, a->action_type, a->terminal);
661 }
662
663 /* NOTE that if CONFIG_FEATURE_USE_INITTAB is NOT defined,
664 * then parse_inittab() simply adds in some default
665 * actions (i.e., runs INIT_SCRIPT and then starts a pair
666 * of "askfirst" shells). If CONFIG_FEATURE_USE_INITTAB
667 * _is_ defined, but /etc/inittab is missing, this
668 * results in the same set of default behaviors.
669 */
parse_inittab(void)670 static void parse_inittab(void)
671 {
672 #if ENABLE_FEATURE_USE_INITTAB
673 char *token[4];
674 parser_t *parser = config_open2("/etc/inittab", fopen_for_read);
675
676 if (parser == NULL)
677 #endif
678 {
679 /* No inittab file - set up some default behavior */
680 /* Sysinit */
681 new_init_action(SYSINIT, INIT_SCRIPT, "");
682 /* Askfirst shell on tty1-4 */
683 new_init_action(ASKFIRST, bb_default_login_shell, "");
684 //TODO: VC_1 instead of ""? "" is console -> ctty problems -> angry users
685 new_init_action(ASKFIRST, bb_default_login_shell, VC_2);
686 new_init_action(ASKFIRST, bb_default_login_shell, VC_3);
687 new_init_action(ASKFIRST, bb_default_login_shell, VC_4);
688 /* Reboot on Ctrl-Alt-Del */
689 new_init_action(CTRLALTDEL, "reboot", "");
690 /* Umount all filesystems on halt/reboot */
691 new_init_action(SHUTDOWN, "umount -a -r", "");
692 /* Swapoff on halt/reboot */
693 new_init_action(SHUTDOWN, "swapoff -a", "");
694 /* Restart init when a QUIT is received */
695 new_init_action(RESTART, "init", "");
696 return;
697 }
698
699 #if ENABLE_FEATURE_USE_INITTAB
700 /* optional_tty:ignored_runlevel:action:command
701 * Delims are not to be collapsed and need exactly 4 tokens
702 */
703 while (config_read(parser, token, 4, 0, "#:",
704 PARSE_NORMAL & ~(PARSE_TRIM | PARSE_COLLAPSE))) {
705 /* order must correspond to SYSINIT..RESTART constants */
706 static const char actions[] ALIGN1 =
707 "sysinit\0""wait\0""once\0""respawn\0""askfirst\0"
708 "ctrlaltdel\0""shutdown\0""restart\0";
709 int action;
710 char *tty = token[0];
711
712 if (!token[3]) /* less than 4 tokens */
713 goto bad_entry;
714 action = index_in_strings(actions, token[2]);
715 if (action < 0 || !token[3][0]) /* token[3]: command */
716 goto bad_entry;
717 /* turn .*TTY -> /dev/TTY */
718 if (tty[0]) {
719 tty = concat_path_file("/dev/", skip_dev_pfx(tty));
720 }
721 new_init_action(1 << action, token[3], tty);
722 if (tty[0])
723 free(tty);
724 continue;
725 bad_entry:
726 message(L_LOG | L_CONSOLE, "Bad inittab entry at line %d",
727 parser->lineno);
728 }
729 config_close(parser);
730 #endif
731 }
732
733 static void pause_and_low_level_reboot(unsigned magic) NORETURN;
pause_and_low_level_reboot(unsigned magic)734 static void pause_and_low_level_reboot(unsigned magic)
735 {
736 pid_t pid;
737
738 /* Allow time for last message to reach serial console, etc */
739 sleep1();
740
741 /* We have to fork here, since the kernel calls do_exit(EXIT_SUCCESS)
742 * in linux/kernel/sys.c, which can cause the machine to panic when
743 * the init process exits... */
744 pid = vfork();
745 if (pid == 0) { /* child */
746 reboot(magic);
747 _exit(EXIT_SUCCESS);
748 }
749 /* Used to have "while (1) sleep(1)" here.
750 * However, in containers reboot() call is ignored, and with that loop
751 * we would eternally sleep here - not what we want.
752 */
753 waitpid(pid, NULL, 0);
754 sleep1(); /* paranoia */
755 _exit(EXIT_SUCCESS);
756 }
757
run_shutdown_and_kill_processes(void)758 static void run_shutdown_and_kill_processes(void)
759 {
760 /* Run everything to be run at "shutdown". This is done _prior_
761 * to killing everything, in case people wish to use scripts to
762 * shut things down gracefully... */
763 run_actions(SHUTDOWN);
764
765 message(L_CONSOLE | L_LOG, "The system is going down NOW!");
766
767 /* Send signals to every process _except_ pid 1 */
768 kill(-1, SIGTERM);
769 message(L_CONSOLE, "Sent SIG%s to all processes", "TERM");
770 sync();
771 sleep1();
772
773 kill(-1, SIGKILL);
774 message(L_CONSOLE, "Sent SIG%s to all processes", "KILL");
775 sync();
776 /*sleep1(); - callers take care about making a pause */
777 }
778
779 /* Signal handling by init:
780 *
781 * For process with PID==1, on entry kernel sets all signals to SIG_DFL
782 * and unmasks all signals. However, for process with PID==1,
783 * default action (SIG_DFL) on any signal is to ignore it,
784 * even for special signals SIGKILL and SIGCONT.
785 * Also, any signal can be caught or blocked.
786 * (but SIGSTOP is still handled specially, at least in 2.6.20)
787 *
788 * We install two kinds of handlers, "immediate" and "delayed".
789 *
790 * Immediate handlers execute at any time, even while, say, sysinit
791 * is running.
792 *
793 * Delayed handlers just set a flag variable. The variable is checked
794 * in the main loop and acted upon.
795 *
796 * SIGSTOP and SIGTSTP have immediate handlers. They just wait
797 * for SIGCONT to happen.
798 *
799 * halt/poweroff/reboot and restart have delayed handlers.
800 *
801 * SIGHUP has a delayed handler, because modifying linked list
802 * of struct action's from a signal handler while it is manipulated
803 * by the program may be disastrous.
804 *
805 * Ctrl-Alt-Del has a delayed handler. Not a must, but allowing
806 * it to happen even somewhere inside "sysinit" would be a bit awkward.
807 */
808
809 /* The SIGPWR/SIGUSR[12]/SIGTERM handler */
810 static void halt_reboot_pwoff(int sig) NORETURN;
halt_reboot_pwoff(int sig)811 static void halt_reboot_pwoff(int sig)
812 {
813 const char *m;
814 unsigned rb;
815
816 /* We may call run() and it unmasks signals,
817 * including the one masked inside this signal handler.
818 * Testcase which would start multiple reboot scripts:
819 * while true; do reboot; done
820 * Preventing it:
821 */
822 reset_sighandlers_and_unblock_sigs();
823
824 run_shutdown_and_kill_processes();
825
826 m = "halt";
827 rb = RB_HALT_SYSTEM;
828 if (sig == SIGTERM) {
829 m = "reboot";
830 rb = RB_AUTOBOOT;
831 } else if (sig == SIGUSR2) {
832 m = "poweroff";
833 rb = RB_POWER_OFF;
834 }
835 message(L_CONSOLE, "Requesting system %s", m);
836 pause_and_low_level_reboot(rb);
837 /* not reached */
838 }
839
840 /* Handler for QUIT - exec "restart" action,
841 * else (no such action defined) do nothing */
exec_restart_action(void)842 static void exec_restart_action(void)
843 {
844 struct init_action *a;
845
846 for (a = G.init_action_list; a; a = a->next) {
847 if (!(a->action_type & RESTART))
848 continue;
849
850 /* Starting from here, we won't return.
851 * Thus don't need to worry about preserving errno
852 * and such.
853 */
854
855 reset_sighandlers_and_unblock_sigs();
856
857 run_shutdown_and_kill_processes();
858
859 #ifdef RB_ENABLE_CAD
860 /* Allow Ctrl-Alt-Del to reboot the system.
861 * This is how kernel sets it up for init, we follow suit.
862 */
863 reboot(RB_ENABLE_CAD); /* misnomer */
864 #endif
865
866 if (open_stdio_to_tty(a->terminal)) {
867 dbg_message(L_CONSOLE, "Trying to re-exec %s", a->command);
868 /* Theoretically should be safe.
869 * But in practice, kernel bugs may leave
870 * unkillable processes, and wait() may block forever.
871 * Oh well. Hoping "new" init won't be too surprised
872 * by having children it didn't create.
873 */
874 //while (wait(NULL) > 0)
875 // continue;
876 init_exec(a->command);
877 }
878 /* Open or exec failed */
879 pause_and_low_level_reboot(RB_HALT_SYSTEM);
880 /* not reached */
881 }
882 }
883
884 /* The SIGSTOP/SIGTSTP handler
885 * NB: inside it, all signals except SIGCONT are masked
886 * via appropriate setup in sigaction().
887 */
stop_handler(int sig UNUSED_PARAM)888 static void stop_handler(int sig UNUSED_PARAM)
889 {
890 int saved_errno = errno;
891
892 bb_got_signal = 0;
893 signal(SIGCONT, record_signo);
894
895 while (1) {
896 pid_t wpid;
897
898 if (bb_got_signal == SIGCONT)
899 break;
900 /* NB: this can accidentally wait() for a process
901 * which we waitfor() elsewhere! waitfor() must have
902 * code which is resilient against this.
903 */
904 wpid = wait_any_nohang(NULL);
905 mark_terminated(wpid);
906 if (wpid <= 0) /* no processes exited? sleep a bit */
907 sleep1();
908 }
909
910 signal(SIGCONT, SIG_DFL);
911 errno = saved_errno;
912 }
913
914 #if ENABLE_FEATURE_USE_INITTAB
reload_inittab(void)915 static void reload_inittab(void)
916 {
917 struct init_action *a, **nextp;
918
919 message(L_LOG, "reloading /etc/inittab");
920
921 /* Disable old entries */
922 for (a = G.init_action_list; a; a = a->next)
923 a->action_type = 0;
924
925 /* Append new entries, or modify existing entries
926 * (incl. setting a->action_type) if cmd and device name
927 * match new ones. End result: only entries with
928 * a->action_type == 0 are stale.
929 */
930 parse_inittab();
931
932 #if ENABLE_FEATURE_KILL_REMOVED
933 /* Kill stale entries */
934 /* Be nice and send SIGTERM first */
935 for (a = G.init_action_list; a; a = a->next)
936 if (a->action_type == 0 && a->pid != 0)
937 kill(a->pid, SIGTERM);
938 if (CONFIG_FEATURE_KILL_DELAY) {
939 /* NB: parent will wait in NOMMU case */
940 if ((BB_MMU ? fork() : vfork()) == 0) { /* child */
941 sleep(CONFIG_FEATURE_KILL_DELAY);
942 for (a = G.init_action_list; a; a = a->next)
943 if (a->action_type == 0 && a->pid != 0)
944 kill(a->pid, SIGKILL);
945 _exit(EXIT_SUCCESS);
946 }
947 }
948 #endif
949
950 /* Remove stale entries and SYSINIT entries.
951 * We never rerun SYSINIT entries anyway,
952 * removing them too saves a few bytes
953 */
954 nextp = &G.init_action_list;
955 while ((a = *nextp) != NULL) {
956 /*
957 * Why pid == 0 check?
958 * Process can be removed from inittab and added *later*.
959 * If we delete its entry but process still runs,
960 * duplicate is spawned when the entry is re-added.
961 */
962 if ((a->action_type & ~SYSINIT) == 0 && a->pid == 0) {
963 *nextp = a->next;
964 free(a);
965 } else {
966 nextp = &a->next;
967 }
968 }
969
970 /* Not needed: */
971 /* run_actions(RESPAWN | ASKFIRST); */
972 /* - we return to main loop, which does this automagically */
973 }
974 #endif
975
check_delayed_sigs(struct timespec * ts)976 static void check_delayed_sigs(struct timespec *ts)
977 {
978 int sig = sigtimedwait(&G.delayed_sigset, /* siginfo_t */ NULL, ts);
979 if (sig <= 0)
980 return;
981
982 /* The signal "sig" was caught */
983
984 #if ENABLE_FEATURE_USE_INITTAB
985 if (sig == SIGHUP)
986 reload_inittab();
987 #endif
988 if (sig == SIGINT)
989 run_actions(CTRLALTDEL);
990 if (sig == SIGQUIT) {
991 exec_restart_action();
992 /* returns only if no restart action defined */
993 }
994 if ((1 << sig) & (0
995 #ifdef SIGPWR
996 | (1 << SIGPWR)
997 #endif
998 | (1 << SIGUSR1)
999 | (1 << SIGUSR2)
1000 | (1 << SIGTERM)
1001 )) {
1002 halt_reboot_pwoff(sig);
1003 }
1004 /* if (sig == SIGCHLD) do nothing */
1005 }
1006
1007 #if DEBUG_SEGV_HANDLER
handle_sigsegv(int sig,siginfo_t * info,void * ucontext)1008 static void handle_sigsegv(int sig, siginfo_t *info, void *ucontext)
1009 {
1010 long ip;
1011 ucontext_t *uc;
1012
1013 uc = ucontext;
1014 ip = uc->uc_mcontext.gregs[REG_EIP];
1015 fdprintf(2, "signal:%d address:0x%lx ip:0x%lx\n",
1016 sig,
1017 /* this is void*, but using %p would print "(null)"
1018 * even for ptrs which are not exactly 0, but, say, 0x123:
1019 */
1020 (long)info->si_addr,
1021 ip);
1022 {
1023 /* glibc extension */
1024 void *array[50];
1025 int size;
1026 size = backtrace(array, 50);
1027 backtrace_symbols_fd(array, size, 2);
1028 }
1029 for (;;) sleep(9999);
1030 }
1031 #endif
1032
sleep_much(void)1033 static void sleep_much(void)
1034 {
1035 sleep(30 * 24*60*60);
1036 }
1037
1038 int init_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
init_main(int argc UNUSED_PARAM,char ** argv)1039 int init_main(int argc UNUSED_PARAM, char **argv)
1040 {
1041 struct sigaction sa;
1042
1043 INIT_G();
1044
1045 /* Some users send poweroff signals to init VERY early.
1046 * To handle this, mask signals early.
1047 */
1048 /* sigemptyset(&G.delayed_sigset); - done by INIT_G() */
1049 sigaddset(&G.delayed_sigset, SIGINT); /* Ctrl-Alt-Del */
1050 sigaddset(&G.delayed_sigset, SIGQUIT); /* re-exec another init */
1051 #ifdef SIGPWR
1052 sigaddset(&G.delayed_sigset, SIGPWR); /* halt */
1053 #endif
1054 sigaddset(&G.delayed_sigset, SIGUSR1); /* halt */
1055 sigaddset(&G.delayed_sigset, SIGTERM); /* reboot */
1056 sigaddset(&G.delayed_sigset, SIGUSR2); /* poweroff */
1057 #if ENABLE_FEATURE_USE_INITTAB
1058 sigaddset(&G.delayed_sigset, SIGHUP); /* reread /etc/inittab */
1059 #endif
1060 sigaddset(&G.delayed_sigset, SIGCHLD); /* make sigtimedwait() exit on SIGCHLD */
1061 sigprocmask(SIG_BLOCK, &G.delayed_sigset, NULL);
1062
1063 #if DEBUG_SEGV_HANDLER
1064 memset(&sa, 0, sizeof(sa));
1065 sa.sa_sigaction = handle_sigsegv;
1066 sa.sa_flags = SA_SIGINFO;
1067 sigaction_set(SIGSEGV, &sa);
1068 sigaction_set(SIGILL, &sa);
1069 sigaction_set(SIGFPE, &sa);
1070 sigaction_set(SIGBUS, &sa);
1071 #endif
1072
1073 if (argv[1] && strcmp(argv[1], "-q") == 0) {
1074 return kill(1, SIGHUP);
1075 }
1076
1077 #if !DEBUG_INIT
1078 /* Expect to be invoked as init with PID=1 or be invoked as linuxrc */
1079 if (getpid() != 1
1080 && (!ENABLE_LINUXRC || applet_name[0] != 'l') /* not linuxrc? */
1081 ) {
1082 bb_simple_error_msg_and_die("must be run as PID 1");
1083 }
1084
1085 # ifdef RB_DISABLE_CAD
1086 /* Turn off rebooting via CTL-ALT-DEL - we get a
1087 * SIGINT on CAD so we can shut things down gracefully... */
1088 reboot(RB_DISABLE_CAD); /* misnomer */
1089 # endif
1090 #endif
1091
1092 /* If, say, xmalloc would ever die, we don't want to oops kernel
1093 * by exiting.
1094 * NB: we set die_func *after* PID 1 check and bb_show_usage.
1095 * Otherwise, for example, "init u" ("please rexec yourself"
1096 * command for sysvinit) will show help text (which isn't too bad),
1097 * *and sleep forever* (which is bad!)
1098 */
1099 die_func = sleep_much;
1100
1101 /* Figure out where the default console should be */
1102 console_init();
1103 set_sane_term();
1104 xchdir("/");
1105 setsid();
1106
1107 /* Make sure environs is set to something sane */
1108 putenv((char *) "HOME=/");
1109 putenv((char *) bb_PATH_root_path);
1110 putenv((char *) "SHELL=/bin/sh");
1111 putenv((char *) "USER=root"); /* needed? why? */
1112
1113 if (argv[1])
1114 xsetenv("RUNLEVEL", argv[1]);
1115
1116 #if !ENABLE_FEATURE_INIT_QUIET
1117 /* Hello world */
1118 message(L_CONSOLE | L_LOG, "init started: %s", bb_banner);
1119 #endif
1120
1121 /* Check if we are supposed to be in single user mode */
1122 if (argv[1]
1123 && (strcmp(argv[1], "single") == 0 || strcmp(argv[1], "-s") == 0 || LONE_CHAR(argv[1], '1'))
1124 ) {
1125 /* ??? shouldn't we set RUNLEVEL="b" here? */
1126 /* Start a shell on console */
1127 new_init_action(RESPAWN, bb_default_login_shell, "");
1128 } else {
1129 /* Not in single user mode - see what inittab says */
1130
1131 /* NOTE that if CONFIG_FEATURE_USE_INITTAB is NOT defined,
1132 * then parse_inittab() simply adds in some default
1133 * actions (i.e., INIT_SCRIPT and a pair
1134 * of "askfirst" shells) */
1135 parse_inittab();
1136 }
1137
1138 #if ENABLE_SELINUX
1139 if (getenv("SELINUX_INIT") == NULL) {
1140 int enforce = 0;
1141
1142 putenv((char*)"SELINUX_INIT=YES");
1143 if (selinux_init_load_policy(&enforce) == 0) {
1144 BB_EXECVP(argv[0], argv);
1145 } else if (enforce > 0) {
1146 /* SELinux in enforcing mode but load_policy failed */
1147 message(L_CONSOLE, "can't load SELinux Policy. "
1148 "Machine is in enforcing mode. Halting now.");
1149 return EXIT_FAILURE;
1150 }
1151 }
1152 #endif
1153
1154 #if ENABLE_FEATURE_INIT_MODIFY_CMDLINE
1155 /* Make the command line just say "init" - that's all, nothing else */
1156 strncpy(argv[0], "init", strlen(argv[0]));
1157 /* Wipe argv[1]-argv[N] so they don't clutter the ps listing */
1158 while (*++argv)
1159 nuke_str(*argv);
1160 #endif
1161
1162 /* Set up STOP signal handlers */
1163 /* Stop handler must allow only SIGCONT inside itself */
1164 memset(&sa, 0, sizeof(sa));
1165 sigfillset(&sa.sa_mask);
1166 sigdelset(&sa.sa_mask, SIGCONT);
1167 sa.sa_handler = stop_handler;
1168 sa.sa_flags = SA_RESTART;
1169 sigaction_set(SIGTSTP, &sa); /* pause */
1170 /* Does not work as intended, at least in 2.6.20.
1171 * SIGSTOP is simply ignored by init
1172 * (NB: behavior might differ under strace):
1173 */
1174 sigaction_set(SIGSTOP, &sa); /* pause */
1175
1176 /* Now run everything that needs to be run */
1177 /* First run the sysinit command */
1178 run_actions(SYSINIT);
1179 check_delayed_sigs(&G.zero_ts);
1180 /* Next run anything that wants to block */
1181 run_actions(WAIT);
1182 check_delayed_sigs(&G.zero_ts);
1183 /* Next run anything to be run only once */
1184 run_actions(ONCE);
1185
1186 /* Now run the looping stuff for the rest of forever */
1187 while (1) {
1188 /* (Re)run the respawn/askfirst stuff */
1189 run_actions(RESPAWN | ASKFIRST);
1190
1191 /* Wait for any signal (typically it's SIGCHLD) */
1192 check_delayed_sigs(NULL); /* NULL timespec makes it wait */
1193
1194 /* Wait for any child process(es) to exit */
1195 while (1) {
1196 pid_t wpid;
1197 struct init_action *a;
1198
1199 wpid = waitpid(-1, NULL, WNOHANG);
1200 if (wpid <= 0)
1201 break;
1202
1203 a = mark_terminated(wpid);
1204 if (a) {
1205 message(L_LOG, "process '%s' (pid %u) exited. "
1206 "Scheduling for restart.",
1207 a->command, (unsigned)wpid);
1208 }
1209 }
1210
1211 /* Don't consume all CPU time - sleep a bit */
1212 sleep1();
1213 } /* while (1) */
1214 }
1215
1216 //usage:#define linuxrc_trivial_usage NOUSAGE_STR
1217 //usage:#define linuxrc_full_usage ""
1218
1219 //usage:#define init_trivial_usage
1220 //usage: ""
1221 //usage:#define init_full_usage "\n\n"
1222 //usage: "Init is the first process started during boot. It never exits."
1223 //usage: IF_FEATURE_USE_INITTAB(
1224 //usage: "\n""It (re)spawns children according to /etc/inittab."
1225 //usage: "\n""Signals:"
1226 //usage: "\n""HUP: reload /etc/inittab"
1227 //usage: )
1228 //usage: IF_NOT_FEATURE_USE_INITTAB(
1229 //usage: "\n""This version of init doesn't use /etc/inittab,"
1230 //usage: "\n""has fixed set of processed to run."
1231 //usage: "\n""Signals:"
1232 //usage: )
1233 //usage: "\n""TSTP: stop respawning until CONT"
1234 //usage: "\n""QUIT: re-exec another init"
1235 //usage: "\n""USR1/TERM/USR2/INT: run halt/reboot/poweroff/Ctrl-Alt-Del script"
1236 //usage:
1237 //usage:#define init_notes_usage
1238 //usage: "This version of init is designed to be run only by the kernel.\n"
1239 //usage: "\n"
1240 //usage: "BusyBox init doesn't support multiple runlevels. The runlevels field of\n"
1241 //usage: "the /etc/inittab file is completely ignored by BusyBox init. If you want\n"
1242 //usage: "runlevels, use sysvinit.\n"
1243 //usage: "\n"
1244 //usage: "BusyBox init works just fine without an inittab. If no inittab is found,\n"
1245 //usage: "it has the following default behavior:\n"
1246 //usage: "\n"
1247 //usage: " ::sysinit:/etc/init.d/rcS\n"
1248 //usage: " ::askfirst:/bin/sh\n"
1249 //usage: " ::ctrlaltdel:/sbin/reboot\n"
1250 //usage: " ::shutdown:/sbin/swapoff -a\n"
1251 //usage: " ::shutdown:/bin/umount -a -r\n"
1252 //usage: " ::restart:/sbin/init\n"
1253 //usage: " tty2::askfirst:/bin/sh\n"
1254 //usage: " tty3::askfirst:/bin/sh\n"
1255 //usage: " tty4::askfirst:/bin/sh\n"
1256 //usage: "\n"
1257 //usage: "If you choose to use an /etc/inittab file, the inittab entry format is as follows:\n"
1258 //usage: "\n"
1259 //usage: " <id>:<runlevels>:<action>:<process>\n"
1260 //usage: "\n"
1261 //usage: " <id>:\n"
1262 //usage: "\n"
1263 //usage: " WARNING: This field has a non-traditional meaning for BusyBox init!\n"
1264 //usage: " The id field is used by BusyBox init to specify the controlling tty for\n"
1265 //usage: " the specified process to run on. The contents of this field are\n"
1266 //usage: " appended to \"/dev/\" and used as-is. There is no need for this field to\n"
1267 //usage: " be unique, although if it isn't you may have strange results. If this\n"
1268 //usage: " field is left blank, then the init's stdin/out will be used.\n"
1269 //usage: "\n"
1270 //usage: " <runlevels>:\n"
1271 //usage: "\n"
1272 //usage: " The runlevels field is completely ignored.\n"
1273 //usage: "\n"
1274 //usage: " <action>:\n"
1275 //usage: "\n"
1276 //usage: " Valid actions include: sysinit, respawn, askfirst, wait,\n"
1277 //usage: " once, restart, ctrlaltdel, and shutdown.\n"
1278 //usage: "\n"
1279 //usage: " The available actions can be classified into two groups: actions\n"
1280 //usage: " that are run only once, and actions that are re-run when the specified\n"
1281 //usage: " process exits.\n"
1282 //usage: "\n"
1283 //usage: " Run only-once actions:\n"
1284 //usage: "\n"
1285 //usage: " 'sysinit' is the first item run on boot. init waits until all\n"
1286 //usage: " sysinit actions are completed before continuing. Following the\n"
1287 //usage: " completion of all sysinit actions, all 'wait' actions are run.\n"
1288 //usage: " 'wait' actions, like 'sysinit' actions, cause init to wait until\n"
1289 //usage: " the specified task completes. 'once' actions are asynchronous,\n"
1290 //usage: " therefore, init does not wait for them to complete. 'restart' is\n"
1291 //usage: " the action taken to restart the init process. By default this should\n"
1292 //usage: " simply run /sbin/init, but can be a script which runs pivot_root or it\n"
1293 //usage: " can do all sorts of other interesting things. The 'ctrlaltdel' init\n"
1294 //usage: " actions are run when the system detects that someone on the system\n"
1295 //usage: " console has pressed the CTRL-ALT-DEL key combination. Typically one\n"
1296 //usage: " wants to run 'reboot' at this point to cause the system to reboot.\n"
1297 //usage: " Finally the 'shutdown' action specifies the actions to taken when\n"
1298 //usage: " init is told to reboot. Unmounting filesystems and disabling swap\n"
1299 //usage: " is a very good here.\n"
1300 //usage: "\n"
1301 //usage: " Run repeatedly actions:\n"
1302 //usage: "\n"
1303 //usage: " 'respawn' actions are run after the 'once' actions. When a process\n"
1304 //usage: " started with a 'respawn' action exits, init automatically restarts\n"
1305 //usage: " it. Unlike sysvinit, BusyBox init does not stop processes from\n"
1306 //usage: " respawning out of control. The 'askfirst' actions acts just like\n"
1307 //usage: " respawn, except that before running the specified process it\n"
1308 //usage: " displays the line \"Please press Enter to activate this console.\"\n"
1309 //usage: " and then waits for the user to press enter before starting the\n"
1310 //usage: " specified process.\n"
1311 //usage: "\n"
1312 //usage: " Unrecognized actions (like initdefault) will cause init to emit an\n"
1313 //usage: " error message, and then go along with its business. All actions are\n"
1314 //usage: " run in the order they appear in /etc/inittab.\n"
1315 //usage: "\n"
1316 //usage: " <process>:\n"
1317 //usage: "\n"
1318 //usage: " Specifies the process to be executed and its command line.\n"
1319 //usage: "\n"
1320 //usage: "Example /etc/inittab file:\n"
1321 //usage: "\n"
1322 //usage: " # This is run first except when booting in single-user mode\n"
1323 //usage: " #\n"
1324 //usage: " ::sysinit:/etc/init.d/rcS\n"
1325 //usage: " \n"
1326 //usage: " # /bin/sh invocations on selected ttys\n"
1327 //usage: " #\n"
1328 //usage: " # Start an \"askfirst\" shell on the console (whatever that may be)\n"
1329 //usage: " ::askfirst:-/bin/sh\n"
1330 //usage: " # Start an \"askfirst\" shell on /dev/tty2-4\n"
1331 //usage: " tty2::askfirst:-/bin/sh\n"
1332 //usage: " tty3::askfirst:-/bin/sh\n"
1333 //usage: " tty4::askfirst:-/bin/sh\n"
1334 //usage: " \n"
1335 //usage: " # /sbin/getty invocations for selected ttys\n"
1336 //usage: " #\n"
1337 //usage: " tty4::respawn:/sbin/getty 38400 tty4\n"
1338 //usage: " tty5::respawn:/sbin/getty 38400 tty5\n"
1339 //usage: " \n"
1340 //usage: " \n"
1341 //usage: " # Example of how to put a getty on a serial line (for a terminal)\n"
1342 //usage: " #\n"
1343 //usage: " #::respawn:/sbin/getty -L ttyS0 9600 vt100\n"
1344 //usage: " #::respawn:/sbin/getty -L ttyS1 9600 vt100\n"
1345 //usage: " #\n"
1346 //usage: " # Example how to put a getty on a modem line\n"
1347 //usage: " #::respawn:/sbin/getty 57600 ttyS2\n"
1348 //usage: " \n"
1349 //usage: " # Stuff to do when restarting the init process\n"
1350 //usage: " ::restart:/sbin/init\n"
1351 //usage: " \n"
1352 //usage: " # Stuff to do before rebooting\n"
1353 //usage: " ::ctrlaltdel:/sbin/reboot\n"
1354 //usage: " ::shutdown:/bin/umount -a -r\n"
1355 //usage: " ::shutdown:/sbin/swapoff -a\n"
1356