systemd-gpt-auto-generator(8) — Linux manual page

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SYSTEMD-GPT-AUTO-GENERATOR(8)d-gpt-auto-generatorD-GPT-AUTO-GENERATOR(8)

NAME         top

       systemd-gpt-auto-generator - Generator for automatically
       discovering and mounting root, /home/, /srv/, /var/ and /var/tmp/
       partitions, as well as discovering and enabling swap partitions,
       based on GPT partition type GUIDs

SYNOPSIS         top

       /usr/lib/systemd/system-generators/systemd-gpt-auto-generator

DESCRIPTION         top

       systemd-gpt-auto-generator is a unit generator that automatically
       discovers root, /home/, /srv/, /var/, /var/tmp/, the EFI System
       Partition, the Extended Boot Loader Partition and swap partitions
       and creates mount and swap units for them, based on the partition
       type GUIDs of GUID partition tables (GPT), see UEFI
       Specification[1], chapter 5. It implements the Discoverable
       Partitions Specification[2]. Note that this generator has no
       effect on non-GPT systems, and on specific mount points that are
       directories already containing files. Also, on systems where the
       units are explicitly configured (for example, listed in
       fstab(5)), the units this generator creates are overridden, but
       additional implicit dependencies might be created.

       This generator will only look for the root partition on the same
       physical disk the EFI System Partition (ESP) is located on. Note
       that support from the boot loader is required: the EFI variable
       LoaderDevicePartUUID of the 4a67b082-0a4c-41cf-b6c7-440b29bb8c4f
       vendor UUID is used to determine from which partition, and hence
       the disk from which the system was booted. If the boot loader
       does not set this variable, this generator will not be able to
       autodetect the root partition. See the Boot Loader Interface[3]
       for details.

       Similarly, this generator will only look for the other partitions
       on the same physical disk as the root partition. In this case,
       boot loader support is not required. These partitions will not be
       searched for on systems where the root file system is distributed
       on multiple disks, for example via btrfs RAID.

       systemd-gpt-auto-generator is useful for centralizing file system
       configuration in the partition table and making configuration in
       /etc/fstab or on the kernel command line unnecessary.

       This generator looks for the partitions based on their partition
       type GUID. The following partition type GUIDs are identified:

       Table 1. Partition Type GUIDs
       ┌─────────────────────────────────────┬─────────────────┬─────────────┬────────────────┐
       │Partition Type                       Name            Mount Point Explanation    │
       │GUID                                 │                 │             │                │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │44479540-f297-41b2-9af7-d131d5f0458a │ Root Partition  │ /           │ On 32-bit x86  │
       │                                     │ (x86)           │             │ systems, the   │
       │                                     │                 │             │ first x86 root │
       │                                     │                 │             │ partition on   │
       │                                     │                 │             │ the disk the   │
       │                                     │                 │             │ EFI ESP is     │
       │                                     │                 │             │ located on is  │
       │                                     │                 │             │ mounted to the │
       │                                     │                 │             │ root directory │
       │                                     │                 │             │ /.             │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │4f68bce3-e8cd-4db1-96e7-fbcaf984b709 │ Root Partition  │ /           │ On 64-bit x86  │
       │                                     │ (x86-64)        │             │ systems, the   │
       │                                     │                 │             │ first x86-64   │
       │                                     │                 │             │ root partition │
       │                                     │                 │             │ on the disk    │
       │                                     │                 │             │ the EFI ESP is │
       │                                     │                 │             │ located on is  │
       │                                     │                 │             │ mounted to the │
       │                                     │                 │             │ root directory │
       │                                     │                 │             │ /.             │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │69dad710-2ce4-4e3c-b16c-21a1d49abed3 │ Root Partition  │ /           │ On 32-bit ARM  │
       │                                     │ (32-bit ARM)    │             │ systems, the   │
       │                                     │                 │             │ first ARM root │
       │                                     │                 │             │ partition on   │
       │                                     │                 │             │ the disk the   │
       │                                     │                 │             │ EFI ESP is     │
       │                                     │                 │             │ located on is  │
       │                                     │                 │             │ mounted to the │
       │                                     │                 │             │ root directory │
       │                                     │                 │             │ /.             │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │b921b045-1df0-41c3-af44-4c6f280d3fae │ Root Partition  │ /           │ On 64-bit ARM  │
       │                                     │ (64-bit ARM)    │             │ systems, the   │
       │                                     │                 │             │ first ARM root │
       │                                     │                 │             │ partition on   │
       │                                     │                 │             │ the disk the   │
       │                                     │                 │             │ EFI ESP is     │
       │                                     │                 │             │ located on is  │
       │                                     │                 │             │ mounted to the │
       │                                     │                 │             │ root directory │
       │                                     │                 │             │ /.             │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │993d8d3d-f80e-4225-855a-9daf8ed7ea97 │ Root Partition  │ /           │ On Itanium     │
       │                                     │ (Itanium/IA-64) │             │ systems, the   │
       │                                     │                 │             │ first Itanium  │
       │                                     │                 │             │ root partition │
       │                                     │                 │             │ on the disk    │
       │                                     │                 │             │ the EFI ESP is │
       │                                     │                 │             │ located on is  │
       │                                     │                 │             │ mounted to the │
       │                                     │                 │             │ root directory │
       │                                     │                 │             │ /.             │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │60d5a7fe-8e7d-435c-b714-3dd8162144e1 │ Root Partition  │ /           │ On RISC-V      │
       │                                     │ (RISCV-V 32)    │             │ 32-bit         │
       │                                     │                 │             │ systems, the   │
       │                                     │                 │             │ first RISCV-V  │
       │                                     │                 │             │ 32-bit root    │
       │                                     │                 │             │ partition on   │
       │                                     │                 │             │ the disk the   │
       │                                     │                 │             │ EFI ESP is     │
       │                                     │                 │             │ located on is  │
       │                                     │                 │             │ mounted to the │
       │                                     │                 │             │ root directory │
       │                                     │                 │             │ /.             │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │72ec70a6-cf74-40e6-bd49-4bda08e8f224 │ Root Partition  │ /           │ On RISC-V      │
       │                                     │ (RISCV-V 64)    │             │ 64-bit         │
       │                                     │                 │             │ systems, the   │
       │                                     │                 │             │ first RISCV-V  │
       │                                     │                 │             │ 64-bit root    │
       │                                     │                 │             │ partition on   │
       │                                     │                 │             │ the disk the   │
       │                                     │                 │             │ EFI ESP is     │
       │                                     │                 │             │ located on is  │
       │                                     │                 │             │ mounted to the │
       │                                     │                 │             │ root directory │
       │                                     │                 │             │ /.             │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │933ac7e1-2eb4-4f13-b844-0e14e2aef915 │ Home Partition  │ /home/      │ The first home │
       │                                     │                 │             │ partition on   │
       │                                     │                 │             │ the disk the   │
       │                                     │                 │             │ root partition │
       │                                     │                 │             │ is located on  │
       │                                     │                 │             │ is mounted to  │
       │                                     │                 │             │ /home/.        │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │3b8f8425-20e0-4f3b-907f-1a25a76f98e8 │ Server Data     │ /srv/       │ The first      │
       │                                     │ Partition       │             │ server data    │
       │                                     │                 │             │ partition on   │
       │                                     │                 │             │ the disk the   │
       │                                     │                 │             │ root partition │
       │                                     │                 │             │ is located on  │
       │                                     │                 │             │ is mounted to  │
       │                                     │                 │             │ /srv/.         │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │4d21b016-b534-45c2-a9fb-5c16e091fd2d │ Variable Data   │ /var/       │ The first      │
       │                                     │ Partition       │             │ variable data  │
       │                                     │                 │             │ partition on   │
       │                                     │                 │             │ the disk the   │
       │                                     │                 │             │ root partition │
       │                                     │                 │             │ is located on  │
       │                                     │                 │             │ is mounted to  │
       │                                     │                 │             │ /var/ — under  │
       │                                     │                 │             │ the condition  │
       │                                     │                 │             │ its partition  │
       │                                     │                 │             │ UUID matches   │
       │                                     │                 │             │ the first 128  │
       │                                     │                 │             │ bit of the     │
       │                                     │                 │             │ HMAC-SHA256 of │
       │                                     │                 │             │ the GPT type   │
       │                                     │                 │             │ uuid of this   │
       │                                     │                 │             │ partition      │
       │                                     │                 │             │ keyed by the   │
       │                                     │                 │             │ machine ID of  │
       │                                     │                 │             │ the            │
       │                                     │                 │             │ installation   │
       │                                     │                 │             │ stored in      │
       │                                     │                 │             │ machine-id(5). │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │7ec6f557-3bc5-4aca-b293-16ef5df639d1 │ Temporary Data  │ /var/tmp/   │ The first      │
       │                                     │ Partition       │             │ temporary data │
       │                                     │                 │             │ partition on   │
       │                                     │                 │             │ the disk the   │
       │                                     │                 │             │ root partition │
       │                                     │                 │             │ is located on  │
       │                                     │                 │             │ is mounted to  │
       │                                     │                 │             │ /var/tmp/.     │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │0657fd6d-a4ab-43c4-84e5-0933c84b4f4f │ Swap            │ n/a         │ All swap       │
       │                                     │                 │             │ partitions     │
       │                                     │                 │             │ located on the │
       │                                     │                 │             │ disk the root  │
       │                                     │                 │             │ partition is   │
       │                                     │                 │             │ located on are │
       │                                     │                 │             │ enabled.       │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │c12a7328-f81f-11d2-ba4b-00a0c93ec93b │ EFI System      │ /efi/ or    │ The first ESP  │
       │                                     │ Partition (ESP) │ /boot/      │ located on the │
       │                                     │                 │             │ disk the root  │
       │                                     │                 │             │ partition is   │
       │                                     │                 │             │ located on is  │
       │                                     │                 │             │ mounted to     │
       │                                     │                 │             │ /boot/ or      │
       │                                     │                 │             │ /efi/, see     │
       │                                     │                 │             │ below.         │
       ├─────────────────────────────────────┼─────────────────┼─────────────┼────────────────┤
       │bc13c2ff-59e6-4262-a352-b275fd6f7172 │ Extended Boot   │ /boot/      │ The first      │
       │                                     │ Loader          │             │ Extended Boot  │
       │                                     │ Partition       │             │ Loader         │
       │                                     │                 │             │ Partition is   │
       │                                     │                 │             │ mounted to     │
       │                                     │                 │             │ /boot/, see    │
       │                                     │                 │             │ below.         │
       └─────────────────────────────────────┴─────────────────┴─────────────┴────────────────┘

       This generator understands the following attribute flags for
       partitions:

       Table 2. Partition Attributes
       ┌──────────────────────────────┬────────────────────┬───────────────┬───────────────┐
       │Name                          Value              Applicable to Explanation   │
       ├──────────────────────────────┼────────────────────┼───────────────┼───────────────┤
       │GPT_FLAG_READ_ONLY            │ 0x1000000000000000 │ /, /home/,    │ Partition is  │
       │                              │                    │ /srv/, /var/, │ mounted       │
       │                              │                    │ /var/tmp/,    │ read-only     │
       │                              │                    │ Extended Boot │               │
       │                              │                    │ Loader        │               │
       │                              │                    │ Partition     │               │
       ├──────────────────────────────┼────────────────────┼───────────────┼───────────────┤
       │GPT_FLAG_NO_AUTO              │ 0x8000000000000000 │ /, /home/,    │ Partition is  │
       │                              │                    │ /srv/, /var/, │ not mounted   │
       │                              │                    │ /var/tmp/,    │ automatically │
       │                              │                    │ Extended Boot │               │
       │                              │                    │ Loader        │               │
       │                              │                    │ Partition     │               │
       ├──────────────────────────────┼────────────────────┼───────────────┼───────────────┤
       │GPT_FLAG_NO_BLOCK_IO_PROTOCOL │ 0x0000000000000002 │ EFI System    │ Partition is  │
       │                              │                    │ Partition     │ not mounted   │
       │                              │                    │ (ESP)         │ automatically │
       └──────────────────────────────┴────────────────────┴───────────────┴───────────────┘

       The /home/, /srv/, /var/ and /var/tmp/ partitions may be
       encrypted in LUKS format. In this case, a device mapper device is
       set up under the names /dev/mapper/home, /dev/mapper/srv,
       /dev/mapper/var and /dev/mapper/tmp. Note that this might create
       conflicts if the same partition is listed in /etc/crypttab with a
       different device mapper device name.

       When systemd is running in the initrd the / partition may be
       encrypted in LUKS format as well. In this case, a device mapper
       device is set up under the name /dev/mapper/root, and a
       sysroot.mount is set up that mounts the device under /sysroot.
       For more information, see bootup(7).

       Mount and automount units for the EFI System Partition (ESP) are
       generated on EFI systems. The ESP is mounted to /boot/ (except if
       an Extended Boot Loader partition exists, see below), unless a
       mount point directory /efi/ exists, in which case it is mounted
       there. Since this generator creates an automount unit, the mount
       will only be activated on-demand, when accessed. On systems where
       /boot/ (or /efi/ if it exists) is an explicitly configured mount
       (for example, listed in fstab(5)) or where the /boot/ (or /efi/)
       mount point is non-empty, no mount units are generated.

       If the disk contains an Extended Boot Loader partition, as
       defined in the Boot Loader Specification[4], it is made available
       at /boot/ (by means of an automount point, similar to the ESP,
       see above). If both an EFI System Partition and an Extended Boot
       Loader partition exist the latter is preferably mounted to
       /boot/. Make sure to create both /efi/ and /boot/ to ensure both
       partitions are mounted.

       When using this generator in conjunction with btrfs file systems,
       make sure to set the correct default subvolumes on them, using
       btrfs subvolume set-default.

       systemd-gpt-auto-generator implements systemd.generator(7).

KERNEL COMMAND LINE         top

       systemd-gpt-auto-generator understands the following kernel
       command line parameters:

       systemd.gpt_auto, rd.systemd.gpt_auto
           Those options take an optional boolean argument, and default
           to yes. The generator is enabled by default, and a negative
           value may be used to disable it.

       root=
           When used with the special value "gpt-auto", automatic
           discovery of the root partition based on the GPT partition
           type is enabled. Any other value disables this generator.

       rw, ro
           Mount the root partition read-write or read-only initially.

           Note that unlike most kernel command line options these
           settings do not override configuration in the file system,
           and the file system may be remounted later. See
           systemd-remount-fs.service(8).

SEE ALSO         top

       systemd(1), systemd.mount(5), systemd.swap(5),
       systemd-fstab-generator(8), systemd-cryptsetup@.service(8),
       machine-id(5), cryptsetup(8), fstab(5), btrfs(8)

NOTES         top

        1. UEFI Specification
           https://uefi.org/specifications

        2. Discoverable Partitions Specification
           https://systemd.io/DISCOVERABLE_PARTITIONS

        3. Boot Loader Interface
           https://systemd.io/BOOT_LOADER_INTERFACE

        4. Boot Loader Specification
           https://systemd.io/BOOT_LOADER_SPECIFICATION

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2021-04-01.  (At that
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       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 248                                SYSTEMD-GPT-AUTO-GENERATOR(8)

Pages that refer to this page: file-hierarchy(7)kernel-command-line(7)systemd-boot(7)systemd.directives(7)systemd.generator(7)systemd.index(7)systemd-fstab-generator(8)systemd-remount-fs.service(8)