/etc/repart.d/*.conf /run/repart.d/*.conf /usr/lib/repart.d/*.conf
These definition files are useful for implementing operating system images that are prepared and delivered with minimally sized images (for example lacking any state or swap partitions), and which on first boot automatically take possession of any remaining disk space following a few basic rules.
Currently, support for partition definition files is only implemented for GPT partitition tables.
Partition files are generally matched against any partitions already existing on disk in a simple algorithm: the partition files are sorted by their filename (ignoring the directory prefix), and then compared in order against existing partitions matching the same partition type UUID. Specifically, the first existing partition with a specific partition type UUID is assigned the first definition file with the same partition type UUID, and the second existing partition with a specific type UUID the second partition file with the same type UUID, and so on. Any left-over partition files that have no matching existing partition are assumed to define new partition that shall be created. Such partitions are appended to the end of the partition table, in the order defined by their names utilizing the first partition slot greater than the highest slot number currently in use. Any existing partitions that have no matching partition file are left as they are.
Note that these partition definition files do not describe the contents of the partitions, such as the file system used. Separate mechanisms, such as systemd-growfs(8) and systemd-makefs maybe be used to initialize or grow the file systems inside of these partitions.
Table 1. GPT partition type identifiers
|esp||EFI System Partition|
|xbootldr||Extended Boot Loader Partition|
|home||Home (/home/) partition|
|srv||Server data (/srv/) partition|
|var||Variable data (/var/) partition|
|tmp||Temporary data (/var/tmp/) partition|
|linux-generic||Generic Linux file system partition|
|root||Root file system partition type appropriate for the local architecture (an alias for an architecture root file system partition type listed below, e.g. root-x86-64)|
|root-verity||Verity data for the root file system partition for the local architecture|
|root-secondary||Root file system partition of the secondary architecture of the local architecture (usually the matching 32bit architecture for the local 64bit architecture)|
|root-secondary-verity||Verity data for the root file system partition of the secondary architecture|
|root-x86||Root file system partition for the x86 (32bit, aka i386) architecture|
|root-x86-verity||Verity data for the x86 (32bit) root file system partition|
|root-x86-64||Root file system partition for the x86_64 (64bit, aka amd64) architecture|
|root-x86-64-verity||Verity data for the x86_64 (64bit) root file system partition|
|root-arm||Root file system partition for the ARM (32bit) architecture|
|root-arm-verity||Verity data for the ARM (32bit) root file system partition|
|root-arm64||Root file system partition for the ARM (64bit, aka aarch64) architecture|
|root-arm64-verity||Verity data for the ARM (64bit, aka aarch64) root file system partition|
|root-ia64||Root file system partition for the ia64 architecture|
|root-ia64-verity||Verity data for the ia64 root file system partition|
This setting defaults to
Most of the partition type UUIDs listed above are defined in the Discoverable Partitions Specification.
The Weight= setting is used to distribute available disk space in an "elastic" fashion, based on the disk size and existing partitions. If a partition shall have a fixed size use both SizeMinBytes= and SizeMaxBytes= with the same value in order to fixate the size to one value, in which case the weight has no effect.
Padding is useful if empty space shall be left for later additions or a safety margin at the end of the device or between partitions.
The file specified here must have a size that is a multiple of the basic block size 512 and not be empty. If this option is used, the size allocation algorithm is slightly altered: the partition is created as least as big as required to fit the data in, i.e. the data size is an additional minimum size value taken into consideration for the allocation algorithm, similar to and in addition to the SizeMin= value configured above.
This option has no effect if the partition it is declared for already exists, i.e. existing data is never overwritten. Note that the data is copied in before the partition table is updated, i.e. before the partition actually is persistently created. This provides robustness: it is guaranteed that the partition either doesn't exist or exists fully populated; it is not possible that the partition exists but is not or only partially populated.
Table 2. Specifiers available
|"%a"||Architecture||A short string identifying the architecture of the local system. A string such as x86, x86-64 or arm64. See the architectures defined for ConditionArchitecture= in systemd.unit(5) for a full list.|
|"%b"||Boot ID||The boot ID of the running system, formatted as string. See random(4) for more information.|
|"%B"||Operating system build ID||The operating system build identifier of the running system, as read from the BUILD_ID= field of /etc/os-release. If not set, resolves to an empty string. See os-release(5) for more information.|
|"%H"||Host name||The hostname of the running system.|
|"%l"||Short host name||The hostname of the running system, truncated at the first dot to remove any domain component.|
|"%m"||Machine ID||The machine ID of the running system, formatted as string. See machine-id(5) for more information.|
|"%o"||Operating system ID||The operating system identifier of the running system, as read from the ID= field of /etc/os-release. See os-release(5) for more information.|
|"%v"||Kernel release||Identical to uname -r output.|
|"%w"||Operating system version ID||The operating system version identifier of the running system, as read from the VERSION_ID= field of /etc/os-release. If not set, resolves to an empty string. See os-release(5) for more information.|
|"%W"||Operating system variant ID||The operating system variant identifier of the running system, as read from the VARIANT_ID= field of /etc/os-release. If not set, resolves to an empty string. See os-release(5) for more information.|
|"%%"||Single percent sign||Use "%%" in place of "%" to specify a single percent sign.|
With the following file the root partition is automatically grown to the full disk if possible during boot.
# /usr/lib/repart.d/50-root.conf [Partition] Type=root
Example 2. Create a swap and home partition automatically on boot, if missing
The home partition gets all available disk space while the swap partition gets 1G at most and 64M at least. We set a priority > 0 on the swap partition to ensure the swap partition is not used if not enough space is available. For every three bytes assigned to the home partition the swap partition gets assigned one.
# /usr/lib/repart.d/60-home.conf [Partition] Type=home
# /usr/lib/repart.d/70-swap.conf [Partition] Type=swap SizeMinBytes=64M SizeMaxBytes=1G Priority=1 Weight=333
Example 3. Create B partitions in an A/B Verity setup, if missing
Let's say the vendor intends to update OS images in an A/B setup, i.e. with two root partitions (and two matching Verity partitions) that shall be used alternatingly during upgrades. To minimize image sizes the original image is shipped only with one root and one Verity partition (the "A" set), and the second root and Verity partitions (the "B" set) shall be created on first boot on the free space on the medium.
# /usr/lib/repart.d/50-root.conf [Partition] Type=root SizeMinBytes=512M SizeMaxBytes=512M
# /usr/lib/repart.d/60-root-verity.conf [Partition] Type=root-verity SizeMinBytes=64M SizeMaxBytes=64M
The definitions above cover the "A" set of root partition (of a fixed 512M size) and Verity partition for the root partition (of a fixed 64M size). Let's use symlinks to create the "B" set of partitions, since after all they shall have the same properties and sizes as the "A" set.
# ln -s 50-root.conf /usr/lib/repart.d/70-root-b.conf # ln -s 60-root-verity.conf /usr/lib/repart.d/80-root-verity-b.conf
- Discoverable Partitions Specification