Provided by: systemd_249.11-0ubuntu3.17_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 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 GUID │ Name │ Mount Point │ Explanation │
├──────────────────────────────────────┼────────────────────────┼─────────────────┼────────────────────────┤
│ 44479540-f297-41b2-9af7-d131d5f0458a │ Root Partition (x86) │ / │ On 32-bit 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 systems, │
│ │ (x86-64) │ │ 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 (32-bit │ / │ On 32-bit ARM systems, │
│ │ ARM) │ │ 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 (64-bit │ / │ On 64-bit ARM systems, │
│ │ ARM) │ │ 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 systems, │
│ │ (Itanium/IA-64) │ │ 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 32-bit │
│ │ (RISCV-V 32) │ │ 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 64-bit │
│ │ (RISCV-V 64) │ │ 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 Partition │ /srv/ │ The first 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 variable │
│ │ Partition │ │ 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 temporary │
│ │ Partition │ │ 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 Partition │ /efi/ or /boot/ │ The first ESP located │
│ │ (ESP) │ │ on the disk the root │
│ │ │ │ partition is located │
│ │ │ │ on is mounted to │
│ │ │ │ /boot/ or /efi/, see │
│ │ │ │ below. │
├──────────────────────────────────────┼────────────────────────┼─────────────────┼────────────────────────┤
│ bc13c2ff-59e6-4262-a352-b275fd6f7172 │ Extended Boot Loader │ /boot/ │ The first Extended │
│ │ Partition │ │ Boot 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/, /srv/, │ Partition is mounted │
│ │ │ /var/, /var/tmp/, │ read-only │
│ │ │ Extended Boot Loader │ │
│ │ │ Partition │ │
├───────────────────────────────┼────────────────────┼──────────────────────┼───────────────────────┤
│ GPT_FLAG_NO_AUTO │ 0x8000000000000000 │ /, /home/, /srv/, │ Partition is not │
│ │ │ /var/, /var/tmp/, │ mounted automatically │
│ │ │ Extended Boot Loader │ │
│ │ │ Partition │ │
├───────────────────────────────┼────────────────────┼──────────────────────┼───────────────────────┤
│ GPT_FLAG_NO_BLOCK_IO_PROTOCOL │ 0x0000000000000002 │ EFI System Partition │ Partition is not │
│ │ │ (ESP) │ mounted 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
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
systemd 249 SYSTEMD-GPT-AUTO-GENERATOR(8)