repart.d — Partition Definition Files for Automatic Boot-Time Repartitioning
repart.d/*.conf files describe basic properties of partitions of block
devices of the local system. They may be used to declare types, names and sizes of partitions that shall
service reads these files and attempts to add new partitions currently missing and enlarge existing
partitions according to these definitions. Operation is generally incremental, i.e. when applied, what
exists already is left intact, and partitions are never shrunk, moved or deleted.
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.
The GPT partition type UUID to match. This may be a GPT partition type UUID such as
4f68bce3-e8cd-4db1-96e7-fbcaf984b709, or one of the following special
Table 1. GPT partition type identifiers
|EFI System Partition|
|Extended Boot Loader Partition|
|Server data (|
|Variable data (|
|Temporary data (|
|Generic Linux file system partition|
|Root file system partition type appropriate for the local architecture (an alias for an architecture root file system partition type listed below, e.g. |
|Verity data for the root file system partition for the local architecture|
|Root file system partition of the secondary architecture of the local architecture (usually the matching 32bit architecture for the local 64bit architecture)|
|Verity data for the root file system partition of the secondary architecture|
|Root file system partition for the x86 (32bit, aka i386) architecture|
|Verity data for the x86 (32bit) root file system partition|
|Root file system partition for the x86_64 (64bit, aka amd64) architecture|
|Verity data for the x86_64 (64bit) root file system partition|
|Root file system partition for the ARM (32bit) architecture|
|Verity data for the ARM (32bit) root file system partition|
|Root file system partition for the ARM (64bit, aka aarch64) architecture|
|Verity data for the ARM (64bit, aka aarch64) root file system partition|
|Root file system partition for the ia64 architecture|
|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 textual label to assign to the partition if none is assigned yet. Note that this setting is not used for matching. It is also not used when a label is already set for an existing partition. It is thus only used when a partition is newly created or when an existing one had a no label set (that is: an empty label). If not specified a label derived from the partition type is automatically used. Simple specifier expansion is supported, see below.
The UUID to assign to the partition if none is assigned yet. Note that this setting is not used for matching. It is also not used when a UUID is already set for an existing partition. It is thus only used when a partition is newly created or when an existing one had a all-zero UUID set. If not specified a UUID derived from the partition type is automatically used.
A numeric priority to assign to this partition, in the range -2147483648…2147483647, with smaller values indicating higher priority, and higher values indicating smaller priority. This priority is used in case the configured size constraints on the defined partitions do not permit fitting all partitions onto the available disk space. If the partitions do not fit, the highest numeric partition priority of all defined partitions is determined, and all defined partitions with this priority are removed from the list of new partitions to create (which may be multiple, if the same priority is used for multiple partitions). The fitting algorithm is then tried again. If the partitions still do not fit, the now highest numeric partition priority is determined, and the matching partitions removed too, and so on. Partitions of a priority of 0 or lower are never removed. If all partitions with a priority above 0 are removed and the partitions still do not fit on the device the operation fails. Note that this priority has no effect on ordering partitions, for that use the alphabetical order of the filenames of the partition definition files. Defaults to 0.
A numeric weight to assign to this partition in the range 0…1000000. Available disk
space is assigned the defined partitions according to their relative weights (subject to the size
constraints configured with
that a partition with weight 2000 gets double the space as one with weight 1000, and a partition with
weight 333 a third of that. Defaults to 1000.
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
SizeMaxBytes= with the same
value in order to fixate the size to one value, in which case the weight has no
Weight= but sets a weight for the free space after the
partition (the "padding"). When distributing available space the weights of all partitions and all
defined padding is summed, and then each partition and padding gets the fraction defined by its
weight. Defaults to 0, i.e. by default no padding is applied.
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.
Specifies minimum and maximum size constraints in bytes. Takes the usual K, M, G, T,
… suffixes (to the base of 1024). If
SizeMinBytes= is specified the partition is
created at or grown to at least the specified size. If
SizeMaxBytes= is specified
the partition is created at or grown to at most the specified size. The precise size is determined
through the weight value value configured with
Weight=, see above. When
SizeMinBytes= is set equal to
SizeMaxBytes= the configured
weight has no effect as the partition is explicitly sized to the specified fixed value. Note that
partitions are never created smaller than 4096 bytes, and since partitions are never shrunk the
previous size of the partition (in case the partition already exists) is also enforced as lower bound
for the new size. The values should be specified as multiples of 4096 bytes, and are rounded upwards
(in case of
SizeMinBytes=) or downwards (in case of
SizeMaxBytes=) otherwise. If the backing device does not provide enough space to
fulfill the constraints placing the partition will fail. For partitions that shall be created,
depending on the setting of
Priority= (see above) the partition might be dropped
and the placing algorithm restarted. By default a minimum size constraint of 10M and no maximum size
constraint is set.
Specifies minimum and maximum size constraints in bytes for the free space after the
partition (the "padding"). Semantics are similar to
SizeMaxBytes=, except that unlike partition sizes free space can be shrunk and can
be as small as zero. By default no size constraints on padding are set, so that only
PaddingWeight= determines the size of the padding applied.
Takes a path to a regular file, block device node or directory. If specified and the partition is newly created the data from the specified path is written to the newly created partition, on the block level. If a directory is specified the backing block device of the file system the directory is on is determined and the data read directly from that. This option is useful to efficiently replicate existing file systems on the block level on a new partition, for example to build a simple OS installer or OS image builder.
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.
Takes a boolean argument. If specified the partition is marked for removal during a factory reset operation. This functionality is useful to implement schemes where images can be reset into their original state by removing partitions and creating them anew. Defaults to off.
Specifiers may be used in the
Label= setting. The following expansions are understood:
Table 2. Specifiers available
|"||Architecture||A short string identifying the architecture of the local system. A string such as |
|"||Boot ID||The boot ID of the running system, formatted as string. See random(4) for more information.|
|"||Operating system build ID||The operating system build identifier of the running system, as read from the |
|"||Host name||The hostname of the running system.|
|"||Short host name||The hostname of the running system, truncated at the first dot to remove any domain component.|
|"||Machine ID||The machine ID of the running system, formatted as string. See machine-id(5) for more information.|
|"||Operating system ID||The operating system identifier of the running system, as read from the |
|"||Kernel release||Identical to uname -r output.|
|"||Operating system version ID||The operating system version identifier of the running system, as read from the |
|"||Operating system variant ID||The operating system variant identifier of the running system, as read from the |
|"||Single percent sign||Use "|
Example 1. Grow the root partition to the full disk size at first boot
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