systemd-gpt-auto-generator
source link: https://www.freedesktop.org/software/systemd/man/systemd-gpt-auto-generator.html
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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, chapter 5. It
implements the Discoverable Partitions
Specification. 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 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
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-fbcaf984b709Root 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-21a1d49abed3Root 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-af44-4c6f280d3faeRoot 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-9daf8ed7ea97Root 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-b714-3dd8162144e1Root 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-bd49-4bda08e8f224Root 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-b844-0e14e2aef915Home Partition/home/
The first home partition on the disk the root partition is located on is mounted to /home/
.3b8f8425-20e0-4f3b-907f-1a25a76f98e8Server 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-5c16e091fd2dVariable 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-b293-16ef5df639d1Temporary 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-43c4-84e5-0933c84b4f4fSwapn/aAll swap partitions located on the disk the root partition is located on are enabled.c12a7328-f81f-11d2-ba4b-00a0c93ec93bEFI 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-b275fd6f7172Extended 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
GPT_FLAG_READ_ONLY
0x1000000000000000/
, /home/
, /srv/
, /var/
, /var/tmp/
, Extended Boot Loader PartitionPartition is mounted read-onlyGPT_FLAG_NO_AUTO
0x8000000000000000/
, /home/
, /srv/
, /var/
, /var/tmp/
, Extended Boot Loader PartitionPartition is not mounted automaticallyGPT_FLAG_NO_BLOCK_IO_PROTOCOL
0x0000000000000002EFI System Partition (ESP)Partition is not mounted automaticallyThe /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, 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).
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