1--- 2title: Discoverable Partitions Specification 3category: Concepts 4layout: default 5SPDX-License-Identifier: LGPL-2.1-or-later 6--- 7# The Discoverable Partitions Specification (DPS) 8 9_TL;DR: Let's automatically discover, mount and enable the root partition, 10`/home/`, `/srv/`, `/var/` and `/var/tmp/` and the swap partitions based on 11GUID Partition Tables (GPT)!_ 12 13This specification describes the use of GUID Partition Table (GPT) UUIDs to 14enable automatic discovery of partitions and their intended mountpoints. 15Traditionally Linux has made little use of partition types, mostly just 16defining one UUID for file system/data partitions and another one for swap 17partitions. With this specification, we introduce additional partition types 18for specific uses. This has many benefits: 19 20* OS installers can automatically discover and make sense of partitions of 21 existing Linux installations. 22* The OS can discover and mount the necessary file systems with a non-existent 23 or incomplete `/etc/fstab` file and without the `root=` kernel command line 24 option. 25* Container managers (such as nspawn and libvirt-lxc) can introspect and set up 26 file systems contained in GPT disk images automatically and mount them to the 27 right places, thus allowing booting the same, identical images on bare metal 28 and in Linux containers. This enables true, natural portability of disk 29 images between physical machines and Linux containers. 30* As a help to administrators and users partition manager tools can show more 31 descriptive information about partitions tables. 32 33Note that the OS side of this specification is currently implemented in 34[systemd](https://systemd.io/) 211 and newer in the 35[systemd-gpt-auto-generator(8)](https://www.freedesktop.org/software/systemd/man/systemd-gpt-auto-generator.html) 36generator tool. Note that automatic discovery of the root only works if the 37boot loader communicates this information to the OS, by implementing the 38[Boot Loader Interface](BOOT_LOADER_INTERFACE.md). 39 40## Defined Partition Type UUIDs 41 42| Name | Partition Type UUID | Allowed File Systems | Explanation | 43|------|---------------------|----------------------|-------------| 44| _Root Partition (Alpha)_ | `6523f8ae-3eb1-4e2a-a05a-18b695ae656f` | Any native, optionally in LUKS | On systems with matching architecture, the first partition with this type UUID on the disk containing the active EFI ESP is automatically mounted to the root directory `/`. If the partition is encrypted with LUKS or has dm-verity integrity data (see below), the device mapper file will be named `/dev/mapper/root`. | 45| _Root Partition (ARC)_ | `d27f46ed-2919-4cb8-bd25-9531f3c16534` | ditto | ditto | 46| _Root Partition (32-bit ARM)_ | `69dad710-2ce4-4e3c-b16c-21a1d49abed3` | ditto | ditto | 47| _Root Partition (64-bit ARM/AArch64)_ | `b921b045-1df0-41c3-af44-4c6f280d3fae` | ditto | ditto | 48| _Root Partition (Itanium/IA-64)_ | `993d8d3d-f80e-4225-855a-9daf8ed7ea97` | ditto | ditto | 49| _Root Partition (LoongArch 64-bit)_ | `77055800-792c-4f94-b39a-98c91b762bb6` | ditto | ditto | 50| _Root Partition (32-bit MIPS LittleEndian (mipsel))_ | `37c58c8a-d913-4156-a25f-48b1b64e07f0` | ditto | ditto | 51| _Root Partition (64-bit MIPS LittleEndian (mips64el))_ | `700bda43-7a34-4507-b179-eeb93d7a7ca3` | ditto | ditto | 52| _Root Partition (32-bit PowerPC)_ | `1de3f1ef-fa98-47b5-8dcd-4a860a654d78` | ditto | ditto | 53| _Root Partition (64-bit PowerPC BigEndian)_ | `912ade1d-a839-4913-8964-a10eee08fbd2` | ditto | ditto | 54| _Root Partition (64-bit PowerPC LittleEndian)_ | `c31c45e6-3f39-412e-80fb-4809c4980599` | ditto | ditto | 55| _Root Partition (RISC-V 32-bit)_ | `60d5a7fe-8e7d-435c-b714-3dd8162144e1` | ditto | ditto | 56| _Root Partition (RISC-V 64-bit)_ | `72ec70a6-cf74-40e6-bd49-4bda08e8f224` | ditto | ditto | 57| _Root Partition (s390)_ | `08a7acea-624c-4a20-91e8-6e0fa67d23f9` | ditto | ditto | 58| _Root Partition (s390x)_ | `5eead9a9-fe09-4a1e-a1d7-520d00531306` | ditto | ditto | 59| _Root Partition (TILE-Gx)_ | `c50cdd70-3862-4cc3-90e1-809a8c93ee2c` | ditto | ditto | 60| _Root Partition (x86)_ | `44479540-f297-41b2-9af7-d131d5f0458a` | ditto | ditto | 61| _Root Partition (amd64/x86_64)_ | `4f68bce3-e8cd-4db1-96e7-fbcaf984b709` | ditto | ditto | 62| _`/usr/` Partition (Alpha)_ | `e18cf08c-33ec-4c0d-8246-c6c6fb3da024` | Any native, optionally in LUKS | Similar semantics to root partition, but just the `/usr/` partition. | 63| _`/usr/` Partition (ARC)_ | `7978a683-6316-4922-bbee-38bff5a2fecc` | ditto | ditto | 64| _`/usr/` Partition (32-bit ARM)_ | `7d0359a3-02b3-4f0a-865c-654403e70625` | ditto | ditto | 65| _`/usr/` Partition (64-bit ARM/AArch64)_ | `b0e01050-ee5f-4390-949a-9101b17104e9` | ditto | ditto | 66| _`/usr/` Partition (Itanium/IA-64)_ | `4301d2a6-4e3b-4b2a-bb94-9e0b2c4225ea` | ditto | ditto | 67| _`/usr/` Partition (LoongArch 64-bit)_ | `e611c702-575c-4cbe-9a46-434fa0bf7e3f` | ditto | ditto | 68| _`/usr/` Partition (32-bit MIPS LittleEndian (mipsel))_ | `0f4868e9-9952-4706-979f-3ed3a473e947` | ditto | ditto | 69| _`/usr/` Partition (64-bit MIPS LittleEndian (mips64el))_ | `c97c1f32-ba06-40b4-9f22-236061b08aa8` | ditto | ditto | 70| _`/usr/` Partition (32-bit PowerPC)_ | `7d14fec5-cc71-415d-9d6c-06bf0b3c3eaf` | ditto | ditto | 71| _`/usr/` Partition (64-bit PowerPC BigEndian)_ | `2c9739e2-f068-46b3-9fd0-01c5a9afbcca` | ditto | ditto | 72| _`/usr/` Partition (64-bit PowerPC LittleEndian)_ | `15bb03af-77e7-4d4a-b12b-c0d084f7491c` | ditto | ditto | 73| _`/usr/` Partition (RISC-V 32-bit)_ | `b933fb22-5c3f-4f91-af90-e2bb0fa50702` | ditto | ditto | 74| _`/usr/` Partition (RISC-V 64-bit)_ | `beaec34b-8442-439b-a40b-984381ed097d` | ditto | ditto | 75| _`/usr/` Partition (s390)_ | `cd0f869b-d0fb-4ca0-b141-9ea87cc78d66` | ditto | ditto | 76| _`/usr/` Partition (s390x)_ | `8a4f5770-50aa-4ed3-874a-99b710db6fea` | ditto | ditto | 77| _`/usr/` Partition (TILE-Gx)_ | `55497029-c7c1-44cc-aa39-815ed1558630` | ditto | ditto | 78| _`/usr/` Partition (x86)_ | `75250d76-8cc6-458e-bd66-bd47cc81a812` | ditto | ditto | 79| _`/usr/` Partition (amd64/x86_64)_ | `8484680c-9521-48c6-9c11-b0720656f69e` | ditto | ditto | 80| _Root Verity Partition (Alpha)_ | `fc56d9e9-e6e5-4c06-be32-e74407ce09a5` | A dm-verity superblock followed by hash data | Contains dm-verity integrity hash data for the matching root partition. If this feature is used the partition UUID of the root partition should be the first 128 bits of the root hash of the dm-verity hash data, and the partition UUID of this dm-verity partition should be the final 128 bits of it, so that the root partition and its Verity partition can be discovered easily, simply by specifying the root hash. | 81| _Root Verity Partition (ARC)_ | `24b2d975-0f97-4521-afa1-cd531e421b8d` | ditto | ditto | 82| _Root Verity Partition (32-bit ARM)_ | `7386cdf2-203c-47a9-a498-f2ecce45a2d6` | ditto | ditto | 83| _Root Verity Partition (64-bit ARM/AArch64)_ | `df3300ce-d69f-4c92-978c-9bfb0f38d820` | ditto | ditto | 84| _Root Verity Partition (Itanium/IA-64)_ | `86ed10d5-b607-45bb-8957-d350f23d0571` | ditto | ditto | 85| _Root Verity Partition (LoongArch 64-bit)_ | `f3393b22-e9af-4613-a948-9d3bfbd0c535` | ditto | ditto | 86| _Root Verity Partition (32-bit MIPS LittleEndian (mipsel))_ | `d7d150d2-2a04-4a33-8f12-16651205ff7b` | ditto | ditto | 87| _Root Verity Partition (64-bit MIPS LittleEndian (mips64el))_ | `16b417f8-3e06-4f57-8dd2-9b5232f41aa6` | ditto | ditto | 88| _Root Verity Partition (64-bit PowerPC LittleEndian)_ | `906bd944-4589-4aae-a4e4-dd983917446a` | ditto | ditto | 89| _Root Verity Partition (64-bit PowerPC BigEndian)_ | `9225a9a3-3c19-4d89-b4f6-eeff88f17631` | ditto | ditto | 90| _Root Verity Partition (32-bit PowerPC)_ | `98cfe649-1588-46dc-b2f0-add147424925` | ditto | ditto | 91| _Root Verity Partition (RISC-V 32-bit)_ | `ae0253be-1167-4007-ac68-43926c14c5de` | ditto | ditto | 92| _Root Verity Partition (RISC-V 64-bit)_ | `b6ed5582-440b-4209-b8da-5ff7c419ea3d` | ditto | ditto | 93| _Root Verity Partition (s390x)_ | `b325bfbe-c7be-4ab8-8357-139e652d2f6b` | ditto | ditto | 94| _Root Verity Partition (s390)_ | `7ac63b47-b25c-463b-8df8-b4a94e6c90e1` | ditto | ditto | 95| _Root Verity Partition (TILE-Gx)_ | `966061ec-28e4-4b2e-b4a5-1f0a825a1d84` | ditto | ditto | 96| _Root Verity Partition (amd64/x86_64)_ | `2c7357ed-ebd2-46d9-aec1-23d437ec2bf5` | ditto | ditto | 97| _Root Verity Partition (x86)_ | `d13c5d3b-b5d1-422a-b29f-9454fdc89d76` | ditto | ditto | 98| _`/usr/` Verity Partition (Alpha)_ | `8cce0d25-c0d0-4a44-bd87-46331bf1df67` | A dm-verity superblock followed by hash data | Similar semantics to root Verity partition, but just for the `/usr/` partition. | 99| _`/usr/` Verity Partition (ARC)_ | `fca0598c-d880-4591-8c16-4eda05c7347c` | ditto | ditto | 100| _`/usr/` Verity Partition (32-bit ARM)_ | `c215d751-7bcd-4649-be90-6627490a4c05` | ditto | ditto | 101| _`/usr/` Verity Partition (64-bit ARM/AArch64)_ | `6e11a4e7-fbca-4ded-b9e9-e1a512bb664e` | ditto | ditto | 102| _`/usr/` Verity Partition (Itanium/IA-64)_ | `6a491e03-3be7-4545-8e38-83320e0ea880` | ditto | ditto | 103| _`/usr/` Verity Partition (LoongArch 64-bit)_ | `f46b2c26-59ae-48f0-9106-c50ed47f673d` | ditto | ditto | 104| _`/usr/` Verity Partition (32-bit MIPS LittleEndian (mipsel))_ | `46b98d8d-b55c-4e8f-aab3-37fca7f80752` | ditto | ditto | 105| _`/usr/` Verity Partition (64-bit MIPS LittleEndian (mips64el))_ | `3c3d61fe-b5f3-414d-bb71-8739a694a4ef` | ditto | ditto | 106| _`/usr/` Verity Partition (64-bit PowerPC LittleEndian)_ | `ee2b9983-21e8-4153-86d9-b6901a54d1ce` | ditto | ditto | 107| _`/usr/` Verity Partition (64-bit PowerPC BigEndian)_ | `bdb528a5-a259-475f-a87d-da53fa736a07` | ditto | ditto | 108| _`/usr/` Verity Partition (32-bit PowerPC)_ | `df765d00-270e-49e5-bc75-f47bb2118b09` | ditto | ditto | 109| _`/usr/` Verity Partition (RISC-V 32-bit)_ | `cb1ee4e3-8cd0-4136-a0a4-aa61a32e8730` | ditto | ditto | 110| _`/usr/` Verity Partition (RISC-V 64-bit)_ | `8f1056be-9b05-47c4-81d6-be53128e5b54` | ditto | ditto | 111| _`/usr/` Verity Partition (s390x)_ | `31741cc4-1a2a-4111-a581-e00b447d2d06` | ditto | ditto | 112| _`/usr/` Verity Partition (s390)_ | `b663c618-e7bc-4d6d-90aa-11b756bb1797` | ditto | ditto | 113| _`/usr/` Verity Partition (TILE-Gx)_ | `2fb4bf56-07fa-42da-8132-6b139f2026ae` | ditto | ditto | 114| _`/usr/` Verity Partition (amd64/x86_64)_ | `77ff5f63-e7b6-4633-acf4-1565b864c0e6` | ditto | ditto | 115| _`/usr/` Verity Partition (x86)_ | `8f461b0d-14ee-4e81-9aa9-049b6fb97abd` | ditto | ditto | 116| _Root Verity Signature Partition (Alpha)_ | `d46495b7-a053-414f-80f7-700c99921ef8` | A serialized JSON object, see below | Contains a root hash and a PKCS#7 signature for it, permitting signed dm-verity GPT images. | 117| _Root Verity Signature Partition (ARC)_ | `143a70ba-cbd3-4f06-919f-6c05683a78bc` | ditto | ditto | 118| _Root Verity Signature Partition (32-bit ARM)_ | `42b0455f-eb11-491d-98d3-56145ba9d037` | ditto | ditto | 119| _Root Verity Signature Partition (64-bit ARM/AArch64)_ | `6db69de6-29f4-4758-a7a5-962190f00ce3` | ditto | ditto | 120| _Root Verity Signature Partition (Itanium/IA-64)_ | `e98b36ee-32ba-4882-9b12-0ce14655f46a` | ditto | ditto | 121| _Root Verity Signature Partition (LoongArch 64-bit)_ | `5afb67eb-ecc8-4f85-ae8e-ac1e7c50e7d0` | ditto | ditto | 122| _Root Verity Signature Partition (32-bit MIPS LittleEndian (mipsel))_ | `c919cc1f-4456-4eff-918c-f75e94525ca5` | ditto | ditto | 123| _Root Verity Signature Partition (64-bit MIPS LittleEndian (mips64el))_ | `904e58ef-5c65-4a31-9c57-6af5fc7c5de7` | ditto | ditto | 124| _Root Verity Signature Partition (64-bit PowerPC LittleEndian)_ | `d4a236e7-e873-4c07-bf1d-bf6cf7f1c3c6` | ditto | ditto | 125| _Root Verity Signature Partition (64-bit PowerPC BigEndian)_ | `f5e2c20c-45b2-4ffa-bce9-2a60737e1aaf` | ditto | ditto | 126| _Root Verity Signature Partition (32-bit PowerPC)_ | `1b31b5aa-add9-463a-b2ed-bd467fc857e7` | ditto | ditto | 127| _Root Verity Signature Partition (RISC-V 32-bit)_ | `3a112a75-8729-4380-b4cf-764d79934448` | ditto | ditto | 128| _Root Verity Signature Partition (RISC-V 64-bit)_ | `efe0f087-ea8d-4469-821a-4c2a96a8386a` | ditto | ditto | 129| _Root Verity Signature Partition (s390x)_ | `c80187a5-73a3-491a-901a-017c3fa953e9` | ditto | ditto | 130| _Root Verity Signature Partition (s390)_ | `3482388e-4254-435a-a241-766a065f9960` | ditto | ditto | 131| _Root Verity Signature Partition (TILE-Gx)_ | `b3671439-97b0-4a53-90f7-2d5a8f3ad47b` | ditto | ditto | 132| _Root Verity Signature Partition (amd64/x86_64)_ | `41092b05-9fc8-4523-994f-2def0408b176` | ditto | ditto | 133| _Root Verity Signature Partition (x86)_ | `5996fc05-109c-48de-808b-23fa0830b676` | ditto | ditto | 134| _`/usr/` Verity Signature Partition (Alpha)_ | `5c6e1c76-076a-457a-a0fe-f3b4cd21ce6e` | A serialized JSON object, see below | Similar semantics to root Verity signature partition, but just for the `/usr/` partition. | 135| _`/usr/` Verity Signature Partition (ARC)_ | `94f9a9a1-9971-427a-a400-50cb297f0f35` | ditto | ditto | 136| _`/usr/` Verity Signature Partition (32-bit ARM)_ | `d7ff812f-37d1-4902-a810-d76ba57b975a` | ditto | ditto | 137| _`/usr/` Verity Signature Partition (64-bit ARM/AArch64)_ | `c23ce4ff-44bd-4b00-b2d4-b41b3419e02a` | ditto | ditto | 138| _`/usr/` Verity Signature Partition (Itanium/IA-64)_ | `8de58bc2-2a43-460d-b14e-a76e4a17b47f` | ditto | ditto | 139| _`/usr/` Verity Signature Partition (LoongArch 64-bit)_ | `b024f315-d330-444c-8461-44bbde524e99` | ditto | ditto | 140| _`/usr/` Verity Signature Partition (32-bit MIPS LittleEndian (mipsel))_ | `3e23ca0b-a4bc-4b4e-8087-5ab6a26aa8a9` | ditto | ditto | 141| _`/usr/` Verity Signature Partition (64-bit MIPS LittleEndian (mips64el))_ | `f2c2c7ee-adcc-4351-b5c6-ee9816b66e16` | ditto | ditto | 142| _`/usr/` Verity Signature Partition (64-bit PowerPC LittleEndian)_ | `c8bfbd1e-268e-4521-8bba-bf314c399557` | ditto | ditto | 143| _`/usr/` Verity Signature Partition (64-bit PowerPC BigEndian)_ | `0b888863-d7f8-4d9e-9766-239fce4d58af` | ditto | ditto | 144| _`/usr/` Verity Signature Partition (32-bit PowerPC)_ | `7007891d-d371-4a80-86a4-5cb875b9302e` | ditto | ditto | 145| _`/usr/` Verity Signature Partition (RISC-V 32-bit)_ | `c3836a13-3137-45ba-b583-b16c50fe5eb4` | ditto | ditto | 146| _`/usr/` Verity Signature Partition (RISC-V 64-bit)_ | `d2f9000a-7a18-453f-b5cd-4d32f77a7b32` | ditto | ditto | 147| _`/usr/` Verity Signature Partition (s390x)_ | `3f324816-667b-46ae-86ee-9b0c0c6c11b4` | ditto | ditto | 148| _`/usr/` Verity Signature Partition (s390)_ | `17440e4f-a8d0-467f-a46e-3912ae6ef2c5` | ditto | ditto | 149| _`/usr/` Verity Signature Partition (TILE-Gx)_ | `4ede75e2-6ccc-4cc8-b9c7-70334b087510` | ditto | ditto | 150| _`/usr/` Verity Signature Partition (amd64/x86_64)_ | `e7bb33fb-06cf-4e81-8273-e543b413e2e2` | ditto | ditto | 151| _`/usr/` Verity Signature Partition (x86)_ | `974a71c0-de41-43c3-be5d-5c5ccd1ad2c0` | ditto | ditto | 152| _EFI System Partition_ | `c12a7328-f81f-11d2-ba4b-00a0c93ec93b` | VFAT | The ESP used for the current boot is automatically mounted to `/efi/` (or `/boot/` as fallback), unless a different partition is mounted there (possibly via `/etc/fstab`, or because the Extended Boot Loader Partition — see below — exists) or the directory is non-empty on the root disk. This partition type is defined by the [UEFI Specification](http://www.uefi.org/specifications). | 153| _Extended Boot Loader Partition_ | `bc13c2ff-59e6-4262-a352-b275fd6f7172` | Typically VFAT | The Extended Boot Loader Partition (XBOOTLDR) used for the current boot is automatically mounted to `/boot/`, unless a different partition is mounted there (possibly via `/etc/fstab`) or the directory is non-empty on the root disk. This partition type is defined by the [Boot Loader Specification](BOOT_LOADER_SPECIFICATION.md). | 154| _Swap_ | `0657fd6d-a4ab-43c4-84e5-0933c84b4f4f` | Swap, optionally in LUKS | All swap partitions on the disk containing the root partition are automatically enabled. If the partition is encrypted with LUKS, the device mapper file will be named `/dev/mapper/swap`. This partition type predates the Discoverable Partitions Specification. | 155| _Home Partition_ | `933ac7e1-2eb4-4f13-b844-0e14e2aef915` | Any native, optionally in LUKS | The first partition with this type UUID on the disk containing the root partition is automatically mounted to `/home/`. If the partition is encrypted with LUKS, the device mapper file will be named `/dev/mapper/home`. | 156| _Server Data Partition_ | `3b8f8425-20e0-4f3b-907f-1a25a76f98e8` | Any native, optionally in LUKS | The first partition with this type UUID on the disk containing the root partition is automatically mounted to `/srv/`. If the partition is encrypted with LUKS, the device mapper file will be named `/dev/mapper/srv`. | 157| _Variable Data Partition_ | `4d21b016-b534-45c2-a9fb-5c16e091fd2d` | Any native, optionally in LUKS | The first partition with this type UUID on the disk containing the root partition is automatically mounted to `/var/` — under the condition that its partition UUID matches the first 128 bits of `HMAC-SHA256(machine-id, 0x4d21b016b53445c2a9fb5c16e091fd2d)` (i.e. the SHA256 HMAC hash of the binary type UUID keyed by the machine ID as read from [`/etc/machine-id`](https://www.freedesktop.org/software/systemd/man/machine-id.html). This special requirement is made because `/var/` (unlike the other partition types listed here) is inherently private to a specific installation and cannot possibly be shared between multiple OS installations on the same disk, and thus should be bound to a specific instance of the OS, identified by its machine ID. If the partition is encrypted with LUKS, the device mapper file will be named `/dev/mapper/var`. | 158| _Temporary Data Partition_ | `7ec6f557-3bc5-4aca-b293-16ef5df639d1` | Any native, optionally in LUKS | The first partition with this type UUID on the disk containing the root partition is automatically mounted to `/var/tmp/`. If the partition is encrypted with LUKS, the device mapper file will be named `/dev/mapper/tmp`. Note that the intended mount point is indeed `/var/tmp/`, not `/tmp/`. The latter is typically maintained in memory via `tmpfs` and does not require a partition on disk. In some cases it might be desirable to make `/tmp/` persistent too, in which case it is recommended to make it a symlink or bind mount to `/var/tmp/`, thus not requiring its own partition type UUID. | 159| _Per-user Home Partition_ | `773f91ef-66d4-49b5-bd83-d683bf40ad16` | Any native, optionally in LUKS | A home partition of a user, managed by [`systemd-homed`](https://www.freedesktop.org/software/systemd/man/systemd-homed.html). | 160| _Generic Linux Data Partition_ | `0fc63daf-8483-4772-8e79-3d69d8477de4` | Any native, optionally in LUKS | No automatic mounting takes place for other Linux data partitions. This partition type should be used for all partitions that carry Linux file systems. The installer needs to mount them explicitly via entries in `/etc/fstab`. Optionally, these partitions may be encrypted with LUKS. This partition type predates the Discoverable Partitions Specification. | 161 162Other GPT type IDs might be used on Linux, for example to mark software RAID or 163LVM partitions. The definitions of those GPT types is outside of the scope of 164this specification. 165 166[systemd-id128(1)](https://www.freedesktop.org/software/systemd/man/systemd-id128.html)'s 167`show` command may be used to list those GPT partition type UUIDs. 168 169## Partition Names 170 171For partitions of the types listed above it is recommended to use 172human-friendly, descriptive partition names in the GPT partition table, for 173example "*Home*", "*Server* *Data*", "*Fedora* *Root*" and similar, possibly 174localized. 175 176For the Root/Verity/Verity signature partitions it might make sense to use a 177versioned naming scheme reflecting the OS name and its version, 178e.g. "fooOS_2021.4" or similar. 179 180## Partition Flags 181 182This specification defines three GPT partition flags that may be set for the 183partition types defined above: 184 1851. For the root, `/usr/`, Verity, Verity signature, home, server data, variable 186 data, temporary data, swap and extended boot loader partitions, the 187 partition flag bit 63 ("*no-auto*") may be used to turn off auto-discovery 188 for the specific partition. If set, the partition will not be automatically 189 mounted or enabled. 190 1912. For the root, `/usr/`, Verity, Verity signature home, server data, variable 192 data, temporary data and extended boot loader partitions, the partition flag 193 bit 60 ("*read-only*") may be used to mark a partition for read-only mounts 194 only. If set, the partition will be mounted read-only instead of 195 read-write. Note that the variable data partition and the temporary data 196 partition will generally not be able to serve their purpose if marked 197 read-only, since by their very definition they are supposed to be 198 mutable. (The home and server data partitions are generally assumed to be 199 mutable as well, but the requirement for them is not equally strong.) 200 Because of that, while the read-only flag is defined and supported, it's 201 almost never a good idea to actually use it for these partitions. Also note 202 that Verity and signature partitions are by their semantics always 203 read-only. The flag is hence of little effect for them, and it is 204 recommended to set it unconditionally for the Verity and signature partition 205 types. 206 2073. For the root, `/usr/`, home, server data, variable data, temporary data and 208 extended boot loader partitions, the partition flag bit 59 209 ("*grow-file-system*") may be used to mark a partition for automatic growing 210 of the contained file system to the size of the partition when 211 mounted. Tools that automatically mount disk image with a GPT partition 212 table are suggested to implicitly grow the contained file system to the 213 partition size they are contained in, if they are found to be smaller. This 214 flag is without effect on partitions marked read-only. 215 216Note that the first two flag definitions happen to correspond nicely to the 217same ones used by Microsoft Basic Data Partitions. 218 219All three of these flags generally affect only auto-discovery and automatic 220mounting of disk images. If partitions marked with these flags are mounted 221using low-level commands like 222[mount(8)](https://man7.org/linux/man-pages/man2/mount.8.html) or directly with 223[mount(2)](https://man7.org/linux/man-pages/man2/mount.2.html), they typically 224have no effect. 225 226## Verity 227 228The Root/`/usr/` partition types and their matching Verity and Verity signature 229partitions enable relatively automatic handling of `dm-verity` protected 230setups. These types are defined with two modes of operation in mind: 231 2321. A trusted Verity root hash is passed in externally, for example is specified 233 on the kernel command line that is signed along with the kernel image using 234 SecureBoot PE signing (which in turn is tested against a set of 235 firmware-provided set of signing keys). If so, discovery and setup of a 236 Verity volume may be fully automatic: if the root partition's UUID is chosen 237 to match the first 128 bit of the root hash, and the matching Verity 238 partition UUIDs is chosen to match the last 128bit of the root hash, then 239 automatic discovery and match-up of the two partitions is possible, as the 240 root hash is enough to both find the partitions and then combine them in a 241 Verity volume. In this mode a Verity signature partition is not used and 242 unnecessary. 243 2442. A Verity signature partition is included on the disk, with a signature to be 245 tested against a system-provided set of signing keys. The signature 246 partition primarily contains two fields: the root hash to use, and a PKCS#7 247 signature of it, using a signature key trusted by the OS. If so, discovery 248 and setup of a Verity volume may be fully automatic. First, the specified 249 root hash is validated with the signature and the OS-provided trusted 250 keys. If the signature checks out the root hash is then used in the same way 251 as in the first mode of operation described above. 252 253Both modes of operation may be combined in a single image. This is particularly 254useful for images that shall be usable in two different contexts: for example 255an image that shall be able to boot directly on UEFI systems (in which 256case it makes sense to include the root hash on the kernel command line that is 257included in the signed kernel image to boot, as per mode of operation #1 258above), but also be able to used as image for a container engine (such as 259`systemd-nspawn`), which can use the signature partition to validate the image, 260without making use of the signed kernel image (and thus following mode of 261operation #2). 262 263The Verity signature partition's contents should be a serialized JSON object in 264text form, padded with NUL bytes to the next multiple of 4096 bytes in 265size. Currently three fields are defined for the JSON object: 266 2671. The (mandatory) `rootHash` field should be a string containing the Verity root hash, 268 formatted as series of (lowercase) hex characters. 269 2702. The (mandatory) `signature` field should be a string containing the PKCS#7 271 signature of the root hash, in Base64-encoded DER format. This should be the 272 same format used by the Linux kernel's dm-verity signature logic, i.e. the 273 signed data should be the exact string representation of the hash, as stored 274 in `rootHash` above. 275 2763. The (optional) `certificateFingerprint` field should be a string containing 277 a SHA256 fingerprint of the X.509 certificate for the key that signed the 278 root hash, formatted as series of (lowercase) hex characters (no `:` 279 separators or such). 280 281More fields might be added in later revisions of this specification. 282 283## Suggested Mode of Operation 284 285An *installer* that repartitions the hard disk _should_ use the above UUID 286partition types for appropriate partitions it creates. 287 288An *installer* which supports a "manual partitioning" interface _may_ choose to 289pre-populate the interface with swap, `/home/`, `/srv/`, `/var/tmp/` partitions 290of pre-existing Linux installations, identified with the GPT type UUIDs 291above. The installer should not pre-populate such an interface with any 292identified root, `/usr` or `/var/` partition unless the intention is to 293overwrite an existing operating system that might be installed. 294 295An *installer* _may_ omit creating entries in `/etc/fstab` for root, `/home/`, 296`/srv/`, `/var/`, `/var/tmp` and for the swap partitions if they use these UUID 297partition types, and are the first partitions on the disk of each type. If the 298ESP shall be mounted to `/efi/` (or `/boot/`), it may additionally omit 299creating the entry for it in `/etc/fstab`. If the EFI partition shall not be 300mounted to `/efi/` or `/boot/`, it _must_ create `/etc/fstab` entries for them. 301If other partitions are used (for example for `/usr/local/` or 302`/var/lib/mysql/`), the installer _must_ register these in `/etc/fstab`. The 303`root=` parameter passed to the kernel by the boot loader may be omitted if the 304root partition is the first one on the disk of its type. If the root partition 305is not the first one on the disk, the `root=` parameter _must_ be passed to the 306kernel by the boot loader. An installer that mounts a root, `/usr/`, `/home/`, 307`/srv/`, `/var/`, or `/var/tmp/` file system with the partition types defined 308as above which contains a LUKS header _must_ call the device mapper device 309"root", "usr", "home", "srv", "var" or "tmp", respectively. This is necessary 310to ensure that the automatic discovery will never result in different device 311mapper names than any static configuration by the installer, thus eliminating 312possible naming conflicts and ambiguities. 313 314An *operating* *system* _should_ automatically discover and mount the first 315root partition that does not have the no-auto flag set (as described above) by 316scanning the disk containing the currently used EFI ESP. It _should_ 317automatically discover and mount the first `/usr/`, `/home/`, `/srv/`, `/var/`, 318`/var/tmp/` and swap partitions that do not have the no-auto flag set by 319scanning the disk containing the discovered root partition. It should 320automatically discover and mount the partition containing the currently used 321EFI ESP to `/efi/` (or `/boot/` as fallback). It should automatically discover 322and mount the partition containing the currently used Extended Boot Loader 323Partition to `/boot/`. It _should not_ discover or automatically mount 324partitions with other UUID partition types, or partitions located on other 325disks, or partitions with the no-auto flag set. User configuration shall 326always override automatic discovery and mounting. If a root, `/usr/`, 327`/home/`, `/srv/`, `/boot/`, `/var/`, `/var/tmp/`, `/efi/`, `/boot/` or swap 328partition is listed in `/etc/fstab` or with `root=` on the kernel command line, 329it _must_ take precedence over automatically discovered partitions. If a 330`/home/`, `/usr/`, `/srv/`, `/boot/`, `/var/`, `/var/tmp/`, `/efi/` or `/boot/` 331directory is found to be populated already in the root partition, the automatic 332discovery _must not_ mount any discovered file system over it. Optionally, in 333case of the root, `/usr/` and their Verity partitions instead of strictly 334mounting the first suitable partition an OS might choose to mount the partition 335whose label compares the highest according to `strverscmp()` or a similar 336logic, in order to implement a simple partition-based A/B versioning 337scheme. The precise rules are left for the implementation to decide, but when 338in doubt earlier partitions (by their index) should always win over later 339partitions if the label comparison is inconclusive. 340 341A *container* *manager* should automatically discover and mount the root, 342`/usr/`, `/home/`, `/srv/`, `/var/`, `/var/tmp/` partitions inside a container 343disk image. It may choose to mount any discovered ESP and/or XBOOOTLDR 344partition to `/efi/` or `/boot/`. It should ignore any swap should they be 345included in a container disk image. 346 347If a btrfs file system is automatically discovered and mounted by the operating 348system/container manager it will be mounted with its *default* subvolume. The 349installer should make sure to set the default subvolume correctly using "btrfs 350subvolume set-default". 351 352## Sharing of File Systems between Installations 353 354If two Linux-based operating systems are installed on the same disk, the scheme 355above suggests that they may share the swap, `/home/`, `/srv/`, `/var/tmp/`, 356ESP, XBOOTLDR. However, they should each have their own root, `/usr/` and 357`/var/` partition. 358 359## Frequently Asked Questions 360 361### Why are you taking my `/etc/fstab` away? 362 363We are not. `/etc/fstab` always overrides automatic discovery and is indeed 364mentioned in the specifications. We are simply trying to make the boot and 365installation processes of Linux a bit more robust and self-descriptive. 366 367### Why did you only define the root partition for these listed architectures? 368 369Please submit a patch that adds appropriate partition type UUIDs for the 370architecture of your choice should they be missing so far. The only reason they 371aren't defined yet is that nobody submitted them yet. 372 373### Why define distinct root partition UUIDs for the various architectures? 374 375This allows disk images that may be booted on multiple architectures to use 376discovery of the appropriate root partition on each architecture. 377 378### Doesn't this break multi-boot scenarios? 379 380No, it doesn't. The specification says that installers may not stop creating 381`/etc/fstab` or stop including `root=` on the kernel command line, unless the used 382partitions are the first ones of their type on the disk. Additionally, 383`/etc/fstab` and `root=` both override automatic discovery. Multi-boot is hence 384well supported, since it doesn't change anything for anything but the first 385installation. 386 387That all said, it's not expected that generic installers generally stop setting 388`root=` and creating `/etc/fstab` anyway. The option to drop these configuration 389bits is primarily something for appliance-like devices. However, generic 390installers should *still* set the right GPT partition types for the partitions 391they create so that container managers, partition tools and administrators can 392benefit. Phrased differently, this specification introduces A) the 393*recommendation* to use the newly defined partition types to tag things 394properly and B) the *option* to then drop `root=` and `/etc/fstab`. While we 395advertise A) to *all* installers, we only propose B) for simpler, 396appliance-like installations. 397 398### What partitioning tools will create a DPS-compliant partition table? 399 400As of util-linux 2.25.2, the `fdisk` tool provides type codes to create the 401root, home, and swap partitions that the DPS expects. By default, `fdisk` will 402create an old-style MBR, not a GPT, so typing `l` to list partition types will 403not show the choices to let you set the correct UUID. Make sure to first create 404an empty GPT, then type `l` in order for the DPS-compliant type codes to be 405available. 406 407The `gdisk` tool (from version 1.0.5 onward) and its variants (`sgdisk`, 408`cgdisk`) also support creation of partitions with a matching type code. 409 410## Links 411 412[Boot Loader Specification](BOOT_LOADER_SPECIFICATION.md)<br> 413[Boot Loader Interface](BOOT_LOADER_INTERFACE.md)<br> 414[Safely Building Images](BUILDING_IMAGES.md)<br> 415[`systemd-boot(7)`](https://www.freedesktop.org/software/systemd/man/systemd-boot.html)<br> 416[`bootctl(1)`](https://www.freedesktop.org/software/systemd/man/bootctl.html)<br> 417[`systemd-gpt-auto-generator(8)`](https://www.freedesktop.org/software/systemd/man/systemd-gpt-auto-generator.html) 418