Manpages - systemd-gpt-auto-generator.8

NAME
SYNOPSIS
DESCRIPTION
KERNEL COMMAND LINE
SEE ALSO
NOTES

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

/usr/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 (x86-64)	/	On 64-bit x86 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 (32-bit ARM)	/	On 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 (64-bit ARM)	/	On 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 (Itanium/IA-64)	/	On Itanium 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 (RISCV-V 32)	/	On RISC-V 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 (RISCV-V 64)	/	On RISC-V 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 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 Partition	var	The first 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 Partition	var/tmp	The first 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 Partition (ESP)	efi or boot	The first ESP 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 Loader Partition	boot	The first Extended 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, var, var/tmp, Extended Boot Loader Partition	Partition is mounted read-only
GPT_FLAG_NO_AUTO	0x8000000000000000	, /home, srv, var, var/tmp, Extended Boot Loader Partition	Partition is not mounted automatically
GPT_FLAG_NO_BLOCK_IO_PROTOCOL	0x0000000000000002	EFI System Partition (ESP)	Partition is not 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).