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

NAME | SYNOPSIS | DESCRIPTION | KERNEL COMMAND LINE | SEE ALSO | NOTES | COLOPHON

SYSTEMD-...ENERATOR(8) systemd-gpt-auto-generator SYSTEMD-...ENERATOR(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 the root partition, /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 for more details. It implements
       the Discoverable Partitions Specification[2].

       Note that this generator has no effect on non-GPT systems. It
       will also not create mount point configuration for directories
       which already contain files or if the mount point is explicitly
       configured in fstab(5). If the units this generator creates are
       overridden, for example by units in directories with higher
       precedence, drop-ins and additional dependencies created by this
       generator might still be used.

       This generator will only look for the root partition on the same
       physical disk where the EFI System Partition (ESP) is located.
       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 detect 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                                 │                │             │                   │
       ├──────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
       │ SD_GPT_ROOT_X86_64                   │ Root Partition │ /           │ The first         │
       │ 4f68bce3-e8cd-4db1-96e7-fbcaf984b709 │ (x86-64)       │             │ partition with    │
       │                                      │                │             │ this type         │
       │                                      │                │             │ UUID, located     │
       │                                      │                │             │ on the same       │
       │                                      │                │             │ disk as the       │
       │                                      │                │             │ ESP, is used      │
       │                                      │                │             │ as the root       │
       │                                      │                │             │ file system /     │
       │                                      │                │             │ on AMD64 /        │
       │                                      │                │             │ 64-bit x86        │
       │                                      │                │             │ systems.          │
       ├──────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
       │ SD_GPT_ROOT_ARM64                    │ Root Partition │ /           │ The first         │
       │ b921b045-1df0-41c3-af44-4c6f280d3fae │ (64-bit ARM)   │             │ partition with    │
       │                                      │                │             │ this type         │
       │                                      │                │             │ UUID, located     │
       │                                      │                │             │ on the same       │
       │                                      │                │             │ disk as the       │
       │                                      │                │             │ ESP, is used      │
       │                                      │                │             │ as the root       │
       │                                      │                │             │ file system /     │
       │                                      │                │             │ on AArch64 /      │
       │                                      │                │             │ 64-bit ARM        │
       │                                      │                │             │ systems.          │
       ├──────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
       │ SD_GPT_ROOT_ALPHA SD_GPT_ROOT_ARC    │ root           │ /           │ The first         │
       │ SD_GPT_ROOT_ARM SD_GPT_ROOT_ARM64    │ partitions for │             │ partition with    │
       │ SD_GPT_ROOT_IA64                     │ other          │             │ the type UUID     │
       │ SD_GPT_ROOT_LOONGARCH64              │ architectures  │             │ matching the      │
       │ SD_GPT_ROOT_MIPS SD_GPT_ROOT_MIPS64  │                │             │ architecture,     │
       │ SD_GPT_ROOT_MIPS_LE                  │                │             │ located on the    │
       │ SD_GPT_ROOT_MIPS64_LE                │                │             │ same disk as      │
       │ SD_GPT_ROOT_PARISC SD_GPT_ROOT_PPC   │                │             │ the ESP, is       │
       │ SD_GPT_ROOT_PPC64                    │                │             │ used as the       │
       │ SD_GPT_ROOT_PPC64_LE                 │                │             │ root file         │
       │ SD_GPT_ROOT_RISCV32                  │                │             │ system /. For     │
       │ SD_GPT_ROOT_RISCV64 SD_GPT_ROOT_S390 │                │             │ the full list     │
       │ SD_GPT_ROOT_S390X SD_GPT_ROOT_TILEGX │                │             │ and constant      │
       │ SD_GPT_ROOT_X86 SD_GPT_ROOT_X86_64   │                │             │ values, see       │
       │ SD_GPT_USR_ALPHA SD_GPT_USR_ARC      │                │             │ Discoverable      │
       │ SD_GPT_USR_ARM SD_GPT_USR_IA64       │                │             │ Partitions        │
       │ SD_GPT_USR_LOONGARCH64               │                │             │ Specification[2]. │
       │ SD_GPT_USR_MIPS_LE                   │                │             │                   │
       │ SD_GPT_USR_MIPS64_LE                 │                │             │                   │
       │ SD_GPT_USR_PARISC SD_GPT_USR_PPC     │                │             │                   │
       │ SD_GPT_USR_PPC64 SD_GPT_USR_PPC64_LE │                │             │                   │
       │ SD_GPT_USR_RISCV32                   │                │             │                   │
       │ SD_GPT_USR_RISCV64 SD_GPT_USR_S390   │                │             │                   │
       │ SD_GPT_USR_S390X SD_GPT_USR_TILEGX   │                │             │                   │
       │ SD_GPT_USR_X86                       │                │             │                   │
       ├──────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
       │ SD_GPT_HOME                          │ Home Partition │ /home/      │ The first         │
       │ 933ac7e1-2eb4-4f13-b844-0e14e2aef915 │                │             │ partition with    │
       │                                      │                │             │ this type UUID on │
       │                                      │                │             │ the same disk as  │
       │                                      │                │             │ the ESP is        │
       │                                      │                │             │ mounted to        │
       │                                      │                │             │ /home/.           │
       ├──────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
       │ SD_GPT_SRV                           │ Server Data    │ /srv/       │ The first         │
       │ 3b8f8425-20e0-4f3b-907f-1a25a76f98e8 │ Partition      │             │ partition with    │
       │                                      │                │             │ this type UUID on │
       │                                      │                │             │ the same disk as  │
       │                                      │                │             │ the ESP is        │
       │                                      │                │             │ mounted to /srv/. │
       ├──────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
       │ SD_GPT_VAR                           │ Variable Data  │ /var/       │ The first         │
       │ 4d21b016-b534-45c2-a9fb-5c16e091fd2d │ Partition      │             │ partition with    │
       │                                      │                │             │ this type UUID on │
       │                                      │                │             │ the same disk as  │
       │                                      │                │             │ the ESP 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).    │
       ├──────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
       │ SD_GPT_TMP                           │ Temporary Data │ /var/tmp/   │ The first         │
       │ 7ec6f557-3bc5-4aca-b293-16ef5df639d1 │ Partition      │             │ partition with    │
       │                                      │                │             │ this type UUID on │
       │                                      │                │             │ the same disk as  │
       │                                      │                │             │ the ESP is        │
       │                                      │                │             │ mounted to        │
       │                                      │                │             │ /var/tmp/.        │
       ├──────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
       │ SD_GPT_SWAP                          │ Swap           │ n/a         │ All partitions    │
       │ 0657fd6d-a4ab-43c4-84e5-0933c84b4f4f │                │             │ with this type    │
       │                                      │                │             │ UUID on the same  │
       │                                      │                │             │ disk as the ESP   │
       │                                      │                │             │ are used as swap. │
       ├──────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
       │ SD_GPT_ESP                           │ EFI System     │ /efi/ or    │ The first         │
       │ c12a7328-f81f-11d2-ba4b-00a0c93ec93b │ Partition      │ /boot/      │ partition with    │
       │                                      │ (ESP)          │             │ this type UUID    │
       │                                      │                │             │ located on the    │
       │                                      │                │             │ same disk as the  │
       │                                      │                │             │ root partition is │
       │                                      │                │             │ mounted to /boot/ │
       │                                      │                │             │ or /efi/, see     │
       │                                      │                │             │ below.            │
       ├──────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
       │ SD_GPT_XBOOTLDR                      │ Extended Boot  │ /boot/      │ The first         │
       │ bc13c2ff-59e6-4262-a352-b275fd6f7172 │ Loader         │             │ partition with    │
       │                                      │ Partition      │             │ this type UUID    │
       │                                      │                │             │ located on the    │
       │                                      │                │             │ same disk as the  │
       │                                      │                │             │ root partition is │
       │                                      │                │             │ mounted to        │
       │                                      │                │             │ /boot/, see       │
       │                                      │                │             │ below.            │
       └──────────────────────────────────────┴────────────────┴─────────────┴───────────────────┘

       This generator understands the following attribute flags for
       partitions:

       Table 2. Partition Attribute Flags
       ┌──────────────────────────────────┬───────────────────┬───────────────────┐
       │ Flag                             Applicable to     Explanation       │
       ├──────────────────────────────────┼───────────────────┼───────────────────┤
       │ SD_GPT_FLAG_READ_ONLY            │ /, /home/, /srv/, │ Partition is      │
       │ 0x1000000000000000               │ /var/, /var/tmp/, │ mounted read-only │
       │                                  │ Extended Boot     │                   │
       │                                  │ Loader Partition  │                   │
       ├──────────────────────────────────┼───────────────────┼───────────────────┤
       │ SD_GPT_FLAG_NO_AUTO              │ /, /home/, /srv/, │ Partition is not  │
       │ 0x8000000000000000               │ /var/, /var/tmp/, │ mounted           │
       │                                  │ Extended Boot     │ automatically     │
       │                                  │ Loader Partition  │                   │
       ├──────────────────────────────────┼───────────────────┼───────────────────┤
       │ SD_GPT_FLAG_NO_BLOCK_IO_PROTOCOL │ EFI System        │ Partition is not  │
       │ 0x0000000000000002               │ Partition (ESP)   │ mounted           │
       │                                  │                   │ automatically     │
       └──────────────────────────────────┴───────────────────┴───────────────────┘

       The /home/, /srv/, /var/, /var/tmp/ and swap 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, /dev/mapper/tmp or /dev/mapper/swap. 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 with LUKS 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).

       The root partition can be specified by symlinking
       /run/systemd/volatile-root to /dev/block/$major:$minor. This is
       especially useful if the root mount has been replaced by some
       form of volatile file system (overlayfs).

       Mount and automount units for the EFI System Partition (ESP) and
       Extended Boot Loader Partition (XBOOTLDR) are generated on EFI
       systems. If the disk contains an XBOOTLDR partition, as defined
       in the Boot Loader Specification[4], it is made available at
       /boot/. This generator creates an automount unit; the mount will
       only be activated on-demand when accessed. The mount point will
       be created if necessary.

       The ESP is mounted to /boot/ if that directory exists and is not
       used for XBOOTLDR, and otherwise to /efi/. Same as for /boot/, an
       automount unit is used. The mount point will be created if
       necessary.

       No configuration is created for mount points that are configured
       in fstab(5) or when the target directory contains files.

       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.

       If the system was booted via systemd-stub(7) and the stub
       reported to userspace that the kernel image was measured to a
       TPM2 PCR, then any discovered root and /var/ volume identifiers
       (and volume encryption key in case it is encrypted) will be
       automatically measured into PCR 15 on activation, via
       systemd-pcrfs@.service(8).

       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 false
           value may be used to disable it (e.g.  "systemd.gpt_auto=0").

           Added in version 242.

       systemd.image_policy=, rd.systemd.image_policy=
           Takes an image dissection policy string as argument (as per
           systemd.image-policy(7)), and allows enforcing a policy on
           dissection and use of the automatically discovered GPT
           partition table entries.

           Added in version 254.

       root=, rootfstype=, rootflags=
           When root= is used with the special value "gpt-auto" (or if
           the parameter is not used at all), automatic discovery of the
           root partition based on the GPT partition type is enabled.
           Any other value disables this logic.

           The rootfstype= and rootflags= are used to select the file
           system type and options when the root file system is
           automatically discovered.

           Added in version 242.

       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).

           Added in version 242.

       systemd.swap=
           Takes a boolean argument or enables the option if specified
           without an argument. If disabled, automatic discovery of swap
           partition(s) based on GPT partition type is disabled.
           Defaults to enabled.

           Added in version 254.

SEE ALSO         top

       systemd(1), systemd.mount(5), systemd.swap(5),
       systemd-fstab-generator(8), systemd-cryptsetup@.service(8),
       systemd-pcrfs@.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://uapi-group.org/specifications/specs/discoverable_partitions_specification

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

        4. Boot Loader Specification
           https://uapi-group.org/specifications/specs/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 2023-12-22.  (At that
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       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 255                                       SYSTEMD-...ENERATOR(8)

Pages that refer to this page: repart.d(5)systemd.mount(5)sysupdate.d(5)file-hierarchy(7)kernel-command-line(7)systemd.directives(7)systemd.generator(7)systemd.image-policy(7)systemd.index(7)systemd-fstab-generator(8)systemd-remount-fs.service(8)