Provided by: systemd_252.5-2ubuntu3_amd64 
NAME
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
/lib/systemd/system-generators/systemd-gpt-auto-generator
DESCRIPTION
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 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 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 GUID │ Name │ Mount Point │ Explanation │
├─────────────────────────────────────┼─────────────────────┼─────────────────┼─────────────────────┤
│SD_GPT_ROOT_X86_64 │ Root Partition │ / │ The first partition │
│4f68bce3-e8cd-4db1-96e7-fbcaf984b709 │ (x86-64) │ │ 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 partition │
│b921b045-1df0-41c3-af44-4c6f280d3fae │ (64-bit ARM) │ │ 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 partitions for │ / │ The first partition │
│SD_GPT_ROOT_ARM SD_GPT_ROOT_ARM64 │ other architectures │ │ with the type UUID │
│SD_GPT_ROOT_IA64 │ │ │ matching the │
│SD_GPT_ROOT_LOONGARCH64 │ │ │ architecture, │
│SD_GPT_ROOT_MIPS_LE │ │ │ located on the same │
│SD_GPT_ROOT_MIPS64_LE │ │ │ disk as the ESP, is │
│SD_GPT_ROOT_PARISC SD_GPT_ROOT_PPC │ │ │ used as the root │
│SD_GPT_ROOT_PPC64 │ │ │ file system /. For │
│SD_GPT_ROOT_PPC64_LE │ │ │ the full list and │
│SD_GPT_ROOT_RISCV32 │ │ │ constant values, │
│SD_GPT_ROOT_RISCV64 SD_GPT_ROOT_S390 │ │ │ see Discoverable │
│SD_GPT_ROOT_S390X SD_GPT_ROOT_TILEGX │ │ │ Partitions │
│SD_GPT_ROOT_X86 SD_GPT_ROOT_X86_64 │ │ │ Specification[2]. │
│SD_GPT_USR_ALPHA SD_GPT_USR_ARC │ │ │ │
│SD_GPT_USR_ARM SD_GPT_USR_IA64 │ │ │ │
│SD_GPT_USR_LOONGARCH64 │ │ │ │
│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 partition │
│933ac7e1-2eb4-4f13-b844-0e14e2aef915 │ │ │ with this type UUID │
│ │ │ │ on the same disk as │
│ │ │ │ the ESP is mounted │
│ │ │ │ to /home/. │
├─────────────────────────────────────┼─────────────────────┼─────────────────┼─────────────────────┤
│SD_GPT_SRV │ Server Data │ /srv/ │ The first partition │
│3b8f8425-20e0-4f3b-907f-1a25a76f98e8 │ Partition │ │ with this type UUID │
│ │ │ │ on the same disk as │
│ │ │ │ the ESP is mounted │
│ │ │ │ to /srv/. │
├─────────────────────────────────────┼─────────────────────┼─────────────────┼─────────────────────┤
│SD_GPT_VAR │ Variable Data │ /var/ │ The first partition │
│4d21b016-b534-45c2-a9fb-5c16e091fd2d │ 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 partition │
│7ec6f557-3bc5-4aca-b293-16ef5df639d1 │ 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 with │
│0657fd6d-a4ab-43c4-84e5-0933c84b4f4f │ │ │ this type UUID on │
│ │ │ │ the same disk as │
│ │ │ │ the ESP are used as │
│ │ │ │ swap. │
├─────────────────────────────────────┼─────────────────────┼─────────────────┼─────────────────────┤
│SD_GPT_ESP │ EFI System │ /efi/ or /boot/ │ The first partition │
│c12a7328-f81f-11d2-ba4b-00a0c93ec93b │ Partition (ESP) │ │ with 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 partition │
│bc13c2ff-59e6-4262-a352-b275fd6f7172 │ Loader Partition │ │ with 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/, /var/, │ Partition is mounted │
│0x1000000000000000 │ /var/tmp/, Extended Boot │ read-only │
│ │ Loader Partition │ │
├─────────────────────────────────┼──────────────────────────┼──────────────────────────┤
│SD_GPT_FLAG_NO_AUTO │ /, /home/, /srv/, /var/, │ Partition is not mounted │
│0x8000000000000000 │ /var/tmp/, Extended Boot │ automatically │
│ │ Loader Partition │ │
├─────────────────────────────────┼──────────────────────────┼──────────────────────────┤
│SD_GPT_FLAG_NO_BLOCK_IO_PROTOCOL │ EFI System Partition │ Partition is not mounted │
│0x0000000000000002 │ (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).
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) 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
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
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
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