Provided by: systemd_255.4-1ubuntu8.4_amd64 
NAME
sysupdate.d - Transfer Definition Files for Automatic Updates
SYNOPSIS
/etc/sysupdate.d/*.conf
/run/sysupdate.d/*.conf
/usr/lib/sysupdate.d/*.conf
DESCRIPTION
sysupdate.d/*.conf files describe how specific resources on the local system shall be
updated from a remote source. Each such file defines one such transfer: typically a remote
HTTP/HTTPS resource as source; and a local file, directory or partition as target. This
may be used as a simple, automatic, atomic update mechanism for the OS itself, for
containers, portable services or system extension images — but in fact may be used to
update any kind of file from a remote source.
The systemd-sysupdate(8) command reads these files and uses them to determine which local
resources should be updated, and then executes the update.
Both the remote HTTP/HTTPS source and the local target typically exist in multiple,
concurrent versions, in order to implement flexible update schemes, e.g. A/B updating (or
a superset thereof, e.g. A/B/C, A/B/C/D, ...).
Each *.conf file defines one transfer, i.e. describes one resource to update. Typically,
multiple of these files (i.e. multiple of such transfers) are defined together, and are
bound together by a common version identifier in order to update multiple resources at
once on each update operation, for example to update a kernel, a root file system and a
Verity partition in a single, combined, synchronized operation, so that only a combined
update of all three together constitutes a complete update.
Each *.conf file contains three sections: [Transfer], [Source] and [Target].
BASIC MODE OF OPERATION
Disk-image based OS updates typically consist of multiple different resources that need to
be updated together, for example a secure OS update might consist of a root file system
image to drop into a partition, a matching Verity integrity data partition image, and a
kernel image prepared to boot into the combination of the two partitions. The first two
resources are files that are downloaded and placed in a disk partition, the latter is a
file that is downloaded and placed in a regular file in the boot file system (e.g. EFI
system partition). Hence, during an update of a hypothetical operating system "foobarOS"
to a hypothetical version 47 the following operations should take place:
1. A file "https://download.example.com/foobarOS_47.root.xz" should be downloaded,
decompressed and written to a previously unused partition with GPT partition type UUID
4f68bce3-e8cd-4db1-96e7-fbcaf984b709 for x86-64, as per Discoverable Partitions
Specification[1].
2. Similarly, a file "https://download.example.com/foobarOS_47.verity.xz" should be
downloaded, decompressed and written to a previously empty partition with GPT
partition type UUID of 2c7357ed-ebd2-46d9-aec1-23d437ec2bf5 (i.e. the partition type
for Verity integrity information for x86-64 root file systems).
3. Finally, a file "https://download.example.com/foobarOS_47.efi.xz" (a unified kernel,
as per Boot Loader Specification[2] Type #2) should be downloaded, decompressed and
written to the $BOOT file system, i.e. to EFI/Linux/foobarOS_47.efi in the ESP or
XBOOTLDR partition.
The version-independent generalization of this would be (using the special marker "@v" as
wildcard for the version identifier):
1. A transfer of a file "https://download.example.com/foobarOS_@v.root.xz" → a local,
previously empty GPT partition of type 4f68bce3-e8cd-4db1-96e7-fbcaf984b709, with the
label to be set to "foobarOS_@v".
2. A transfer of a file "https://download.example.com/foobarOS_@v.verity.xz" → a local,
previously empty GPT partition of type 2c7357ed-ebd2-46d9-aec1-23d437ec2bf5, with the
label to be set to "foobarOS_@v_verity".
3. A transfer of a file "https://download.example.com/foobarOS_@v.efi.xz" → a local file
$BOOT/EFI/Linux/foobarOS_@v.efi.
An update can only complete if the relevant URLs provide their resources for the same
version, i.e. for the same value of "@v".
The above may be translated into three *.conf files in sysupdate.d/, one for each resource
to transfer. The *.conf files configure the type of download, and what place to write the
download to (i.e. whether to a partition or a file in the file system). Most importantly
these files contain the URL, partition name and filename patterns shown above that
describe how these resources are called on the source and how they shall be called on the
target.
In order to enumerate available versions and figuring out candidates to update to, a
mechanism is necessary to list suitable files:
• For partitions: the surrounding GPT partition table contains a list of defined
partitions, including a partition type UUID and a partition label (in this scheme the
partition label plays a role for the partition similar to the filename for a regular
file).
• For regular files: the directory listing of the directory the files are contained in
provides a list of existing files in a straightforward way.
• For HTTP/HTTPS sources a simple scheme is used: a manifest file SHA256SUMS, following
the format defined by sha256sum(1), lists file names and their SHA256 hashes.
Transfers are done in the alphabetical order of the .conf file names they are defined in.
First, the resource data is downloaded directly into a target file/directory/partition.
Once this is completed for all defined transfers, in a second step the
files/directories/partitions are renamed to their final names as defined by the target
MatchPattern=, again in the order the .conf transfer file names dictate. This step is not
atomic, however it is guaranteed to be executed strictly in order with suitable disk
synchronization in place. Typically, when updating an OS one of the transfers defines the
entry point when booting. Thus it is generally a good idea to order the resources via the
transfer configuration file names so that the entry point is written last, ensuring that
any abnormal termination does not leave an entry point around whose backing is not
established yet. In the example above it would hence make sense to establish the EFI
kernel image last and thus give its transfer configuration file the alphabetically last
name.
See below for an extended, more specific example based on the above.
RESOURCE TYPES
Each transfer file defines one source resource to transfer to one target resource. The
following resource types are supported:
1. Resources of type "url-file" encapsulate a file on a web server, referenced via a HTTP
or HTTPS URL. When an update takes place, the file is downloaded and decompressed and
then written to the target file or partition. This resource type is only available for
sources, not for targets. The list of available versions of resources of this type is
encoded in SHA256SUMS manifest files, accompanied by SHA256SUMS.gpg detached
signatures.
2. The "url-tar" resource type is similar, but the file must be a .tar archive. When an
update takes place, the file is decompressed and unpacked into a directory or btrfs
subvolume. This resource type is only available for sources, not for targets. Just
like "url-file", "url-tar" version enumeration makes use of SHA256SUMS files,
authenticated via SHA256SUMS.gpg.
3. The "regular-file" resource type encapsulates a local regular file on disk. During
updates the file is uncompressed and written to the target file or partition. This
resource type is available both as source and as target. When updating no integrity or
authentication verification is done for resources of this type.
4. The "partition" resource type is similar to "regular-file", and encapsulates a GPT
partition on disk. When updating, the partition must exist already, and have the
correct GPT partition type. A partition whose GPT partition label is set to "_empty"
is considered empty, and a candidate to place a newly downloaded resource in. The GPT
partition label is used to store version information, once a partition is updated.
This resource type is only available for target resources.
5. The "tar" resource type encapsulates local .tar archive files. When an update takes
place, the files are uncompressed and unpacked into a target directory or btrfs
subvolume. Behaviour of "tar" and "url-tar" is generally similar, but the latter
downloads from remote sources, and does integrity and authentication checks while the
former does not. The "tar" resource type is only available for source resources.
6. The "directory" resource type encapsulates local directory trees. This type is
available both for source and target resources. If an update takes place on a source
resource of this type, a recursive copy of the directory is done.
7. The "subvolume" resource type is identical to "directory", except when used as the
target, in which case the file tree is placed in a btrfs subvolume instead of a plain
directory, if the backing file system supports it (i.e. is btrfs).
As already indicated, only a subset of source and target resource type combinations are
supported:
Table 1. Resource Types
┌─────────────┬─────────────┬───────────┬───────────────┬────────────────┬───────────────┬───────────┬──────────────┐
│Identifier │ Description │ Usable as │ When Used │ When Used │ When Used │ Usable as │ When Used │
│ │ │ Source │ as Source: │ as Source: │ as Source: │ Target │ as Target: │
│ │ │ │ Compatible │ Integrity + │ Decompression │ │ Compatible │
│ │ │ │ Targets │ Authentication │ │ │ Sources │
├─────────────┼─────────────┼───────────┼───────────────┼────────────────┼───────────────┼───────────┼──────────────┤
│url-file │ HTTP/HTTPS │ yes │ regular-file, │ yes │ yes │ no │ - │
│ │ files │ │ partition │ │ │ │ │
├─────────────┼─────────────┼───────────┼───────────────┼────────────────┼───────────────┼───────────┼──────────────┤
│url-tar │ HTTP/HTTPS │ yes │ directory, │ yes │ yes │ no │ - │
│ │ .tar │ │ subvolume │ │ │ │ │
│ │ archives │ │ │ │ │ │ │
├─────────────┼─────────────┼───────────┼───────────────┼────────────────┼───────────────┼───────────┼──────────────┤
│regular-file │ Local files │ yes │ regular-file, │ no │ yes │ yes │ url-file, │
│ │ │ │ partition │ │ │ │ regular-file │
├─────────────┼─────────────┼───────────┼───────────────┼────────────────┼───────────────┼───────────┼──────────────┤
│partition │ Local GPT │ no │ - │ - │ - │ yes │ url-file, │
│ │ partitions │ │ │ │ │ │ regular-file │
├─────────────┼─────────────┼───────────┼───────────────┼────────────────┼───────────────┼───────────┼──────────────┤
│tar │ Local .tar │ yes │ directory, │ no │ yes │ no │ - │
│ │ archives │ │ subvolume │ │ │ │ │
├─────────────┼─────────────┼───────────┼───────────────┼────────────────┼───────────────┼───────────┼──────────────┤
│directory │ Local │ yes │ directory, │ no │ no │ yes │ url-tar, │
│ │ directories │ │ subvolume │ │ │ │ tar, │
│ │ │ │ │ │ │ │ directory, │
│ │ │ │ │ │ │ │ subvolume │
├─────────────┼─────────────┼───────────┼───────────────┼────────────────┼───────────────┼───────────┼──────────────┤
│subvolume │ Local btrfs │ yes │ directory, │ no │ no │ yes │ url-tar, │
│ │ subvolumes │ │ subvolume │ │ │ │ tar, │
│ │ │ │ │ │ │ │ directory, │
│ │ │ │ │ │ │ │ subvolume │
└─────────────┴─────────────┴───────────┴───────────────┴────────────────┴───────────────┴───────────┴──────────────┘
MATCH PATTERNS
Both the source and target resources typically exist in multiple versions concurrently. An
update operation is done whenever the newest of the source versions is newer than the
newest of the target versions. To determine the newest version of the resources a
directory listing, partition listing or manifest listing is used, a subset of qualifying
entries selected from that, and the version identifier extracted from the file names or
partition labels of these selected entries. Subset selection and extraction of the version
identifier (plus potentially other metadata) is done via match patterns, configured in
MatchPattern= in the [Source] and [Target] sections. These patterns are strings that
describe how files or partitions are named, with named wildcards for specific fields such
as the version identifier. The following wildcards are defined:
Table 2. Match Pattern Wildcards
┌─────────┬─────────────────────┬─────────────────────┬─────────────────────┐
│Wildcard │ Description │ Format │ Notes │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@v" │ Version identifier │ Valid version │ Mandatory │
│ │ │ string │ │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@u" │ GPT partition UUID │ Valid 128-Bit UUID │ Only relevant if │
│ │ │ string │ target resource │
│ │ │ │ type chosen as │
│ │ │ │ partition │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@f" │ GPT partition flags │ Formatted │ Only relevant if │
│ │ │ hexadecimal integer │ target resource │
│ │ │ │ type chosen as │
│ │ │ │ partition │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@a" │ GPT partition flag │ Either "0" or "1" │ Controls NoAuto bit │
│ │ NoAuto │ │ of the GPT │
│ │ │ │ partition flags, as │
│ │ │ │ per Discoverable │
│ │ │ │ Partitions │
│ │ │ │ Specification[1]; │
│ │ │ │ only relevant if │
│ │ │ │ target resource │
│ │ │ │ type chosen as │
│ │ │ │ partition │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@g" │ GPT partition flag │ Either "0" or "1" │ Controls │
│ │ GrowFileSystem │ │ GrowFileSystem bit │
│ │ │ │ of the GPT │
│ │ │ │ partition flags, as │
│ │ │ │ per Discoverable │
│ │ │ │ Partitions │
│ │ │ │ Specification[1]; │
│ │ │ │ only relevant if │
│ │ │ │ target resource │
│ │ │ │ type chosen as │
│ │ │ │ partition │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@r" │ Read-only flag │ Either "0" or "1" │ Controls ReadOnly │
│ │ │ │ bit of the GPT │
│ │ │ │ partition flags, as │
│ │ │ │ per Discoverable │
│ │ │ │ Partitions │
│ │ │ │ Specification[1] │
│ │ │ │ and other output │
│ │ │ │ read-only flags, │
│ │ │ │ see ReadOnly= below │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@t" │ File modification │ Formatted decimal │ Only relevant if │
│ │ time │ integer, μs since │ target resource │
│ │ │ UNIX epoch Jan 1st │ type chosen as │
│ │ │ 1970 │ regular-file │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@m" │ File access mode │ Formatted octal │ Only relevant if │
│ │ │ integer, in UNIX │ target resource │
│ │ │ fashion │ type chosen as │
│ │ │ │ regular-file │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@s" │ File size after │ Formatted decimal │ Useful for │
│ │ decompression │ integer │ measuring progress │
│ │ │ │ and to improve │
│ │ │ │ partition │
│ │ │ │ allocation logic │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@d" │ Tries done │ Formatted decimal │ Useful when │
│ │ │ integer │ operating with │
│ │ │ │ kernel image files, │
│ │ │ │ as per Automatic │
│ │ │ │ Boot Assessment[3] │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@l" │ Tries left │ Formatted decimal │ Useful when │
│ │ │ integer │ operating with │
│ │ │ │ kernel image files, │
│ │ │ │ as per Automatic │
│ │ │ │ Boot Assessment[3] │
├─────────┼─────────────────────┼─────────────────────┼─────────────────────┤
│"@h" │ SHA256 hash of │ 64 hexadecimal │ The SHA256 hash of │
│ │ compressed file │ characters │ the compressed │
│ │ │ │ file; not useful │
│ │ │ │ for url-file or │
│ │ │ │ url-tar where the │
│ │ │ │ SHA256 hash is │
│ │ │ │ already included in │
│ │ │ │ the manifest file │
│ │ │ │ anyway │
└─────────┴─────────────────────┴─────────────────────┴─────────────────────┘
Of these wildcards only "@v" must be present in a valid pattern, all other wildcards are
optional. Each wildcard may be used at most once in each pattern. A typical wildcard
matching a file system source image could be "MatchPattern=foobar_@v.raw.xz", i.e. any
file whose name begins with "foobar_", followed by a version ID and suffixed by ".raw.xz".
Do not confuse the "@" pattern matching wildcard prefix with the "%" specifier expansion
prefix. The former encapsulate a variable part of a match pattern string, the latter are
simple shortcuts that are expanded while the drop-in files are parsed. For details about
specifiers, see below.
[TRANSFER] SECTION OPTIONS
This section defines general properties of this transfer.
MinVersion=
Specifies the minimum version to require for this transfer to take place. If the
source or target patterns in this transfer definition match files older than this
version they will be considered obsolete, and never be considered for the update
operation.
Added in version 251.
ProtectVersion=
Takes one or more version strings to mark as "protected". Protected versions are never
removed while making room for new, updated versions. This is useful to ensure that the
currently booted OS version (or auxiliary resources associated with it) is not
replaced/overwritten during updates, in order to avoid runtime file system
corruptions.
Like many of the settings in these configuration files this setting supports specifier
expansion. It's particularly useful to set this setting to one of the "%A", "%B" or
"%w" specifiers to automatically refer to the current OS version of the running
system. See below for details on supported specifiers.
Added in version 251.
Verify=
Takes a boolean, defaults to yes. Controls whether to cryptographically verify
downloaded resources (specifically: validate the GPG signatures for downloaded
SHA256SUMS manifest files, via their detached signature files SHA256SUMS.gpg in
combination with the system keyring /usr/lib/systemd/import-pubring.gpg or
/etc/systemd/import-pubring.gpg).
This option is essential to provide integrity guarantees for downloaded resources and
thus should be left enabled, outside of test environments.
Note that the downloaded payload files are unconditionally checked against the SHA256
hashes listed in the manifest. This option only controls whether the signatures of
these manifests are verified.
This option only has an effect if the source resource type is selected as url-file or
url-tar, as integrity and authentication checking is only available for transfers from
remote sources.
Added in version 251.
[SOURCE] SECTION OPTIONS
This section defines properties of the transfer source.
Type=
Specifies the resource type of the source for the transfer. Takes one of url-file,
url-tar, tar, regular-file, directory or subvolume. For details about the resource
types, see above. This option is mandatory.
Note that only certain combinations of source and target resource types are supported,
see above.
Added in version 251.
Path=
Specifies where to find source versions of this resource.
If the source type is selected as url-file or url-tar this must be a HTTP/HTTPS URL.
The URL is suffixed with /SHA256SUMS to acquire the manifest file, with
/SHA256SUMS.gpg to acquire the detached signature file for it, and with the file names
listed in the manifest file in case an update is executed and a resource shall be
downloaded.
For all other source resource types this must be a local path in the file system,
referring to a local directory to find the versions of this resource in.
Added in version 251.
MatchPattern=
Specifies one or more file name match patterns that select the subset of files that
are update candidates as source for this transfer. See above for details on match
patterns.
This option is mandatory. Any pattern listed must contain at least the "@v" wildcard,
so that a version identifier may be extracted from the filename. All other wildcards
are optional.
If the source type is regular-file or directory, the pattern may contain slash
characters. In this case it will match the file or directory in corresponding
subdirectory. For example "MatchPattern=foo_@v/bar.efi" will match "bar.efi" in
directory "foo_1".
Added in version 251.
[TARGET] SECTION OPTIONS
This section defines properties of the transfer target.
Type=
Specifies the resource type of the target for the transfer. Takes one of partition,
regular-file, directory or subvolume. For details about the resource types, see above.
This option is mandatory.
Note that only certain combinations of source and target resource types are supported,
see above.
Added in version 251.
Path=
Specifies a file system path where to look for already installed versions or place
newly downloaded versions of this configured resource. If Type= is set to partition,
expects a path to a (whole) block device node, or the special string "auto" in which
case the block device which contains the root file system of the currently booted
system is automatically determined and used. If Type= is set to regular-file,
directory or subvolume, must refer to a path in the local file system referencing the
directory to find or place the version files or directories under.
Note that this mechanism cannot be used to create or remove partitions, in case Type=
is set to partition. Partitions must exist already, and a special partition label
"_empty" is used to indicate empty partitions. To automatically generate suitable
partitions on first boot, use a tool such as systemd-repart(8).
Added in version 251.
PathRelativeTo=
Specifies what partition Path= should be relative to. Takes one of root, esp,
xbootldr, or boot. If unspecified, defaults to root.
If set to boot, the specified Path= will be resolved relative to the mount point of
the $BOOT partition (i.e. the ESP or XBOOTLDR), as defined by the Boot Loader
Specification[2].
The values esp, xbootldr, and boot are only supported when Type= is set to
regular-file or directory.
Added in version 254.
MatchPattern=
Specifies one or more file name or partition label match patterns that select the
subset of files or partitions that are update candidates as targets for this transfer.
See above for details on match patterns.
This option is mandatory. Any pattern listed must contain at least the "@v" wildcard,
so that a version identifier may be extracted from the filename. All other wildcards
are optional.
This pattern is both used for matching existing installed versions and for determining
the name of new versions to install. If multiple patterns are specified, the first
specified is used for naming newly installed versions.
If the target type is regular-file or directory, the pattern may contain slash
characters. In this case it will match the file or directory in corresponding
subdirectory. For example "MatchPattern=foo_@v/bar.efi" will match "bar.efi" in
directory "foo_1". Directories in the path will be created when file is installed.
Empty directories will be removed when file is removed.
Added in version 251.
MatchPartitionType=
When the target Type= is chosen as partition, specifies the GPT partition type to look
for. Only partitions of this type are considered, all other partitions are ignored. If
not specified, the GPT partition type linux-generic is used. Accepts either a literal
type UUID or a symbolic type identifier. For a list of supported type identifiers, see
the Type= setting in repart.d(5).
Added in version 251.
PartitionUUID=, PartitionFlags=, PartitionNoAuto=, PartitionGrowFileSystem=
When the target Type= is picked as partition, selects the GPT partition UUID and
partition flags to use for the updated partition. Expects a valid UUID string, a
hexadecimal integer, or booleans, respectively. If not set, but the source match
pattern includes wildcards for these fields (i.e. "@u", "@f", "@a", or "@g"), the
values from the patterns are used. If neither configured with wildcards or these
explicit settings, the values are left untouched. If both the overall PartitionFlags=
flags setting and the individual flag settings PartitionNoAuto= and
PartitionGrowFileSystem= are used (or the wildcards for them), then the latter
override the former, i.e. the individual flag bit overrides the overall flags value.
See Discoverable Partitions Specification[1] for details about these flags.
Note that these settings are not used for matching, they only have effect on newly
written partitions in case a transfer takes place.
Added in version 251.
ReadOnly=
Controls whether to mark the resulting file, subvolume or partition read-only. If the
target type is partition this controls the ReadOnly partition flag, as per
Discoverable Partitions Specification[1], similar to the PartitionNoAuto= and
PartitionGrowFileSystem= flags described above. If the target type is regular-file,
the writable bit is removed from the access mode. If the target type is subvolume, the
subvolume will be marked read-only as a whole. Finally, if the target Type= is
selected as directory, the "immutable" file attribute is set, see chattr(1) for
details.
Added in version 251.
Mode=
The UNIX file access mode to use for newly created files in case the target resource
type is picked as regular-file. Expects an octal integer, in typical UNIX fashion. If
not set, but the source match pattern includes a wildcard for this field (i.e. "@t"),
the value from the pattern is used.
Note that this setting is not used for matching, it only has an effect on newly
written files when a transfer takes place.
Added in version 251.
TriesDone=, TriesLeft=
These options take positive, decimal integers, and control the number of attempts done
and left for this file. These settings are useful for managing kernel images,
following the scheme defined in Automatic Boot Assessment[3], and only have an effect
if the target pattern includes the "@d" or "@l" wildcards.
Added in version 251.
InstancesMax=
Takes a decimal integer equal to or greater than 2. This configures how many
concurrent versions of the resource to keep. Whenever a new update is initiated it is
made sure that no more than the number of versions specified here minus one exist in
the target. Any excess versions are deleted (in case the target Type= of regular-file,
directory, subvolume is used) or emptied (in case the target Type= of partition is
used; emptying in this case simply means to set the partition label to the special
string "_empty"; note that no partitions are actually removed). After an update is
completed the number of concurrent versions of the target resources is equal to or
below the number specified here.
Note that this setting may be set differently for each transfer. However, it generally
is advisable to keep this setting the same for all transfers, since otherwise
incomplete combinations of files or partitions will be left installed.
If the target Type= is selected as partition, the number of concurrent versions to
keep is additionally restricted by the number of partition slots of the right type in
the partition table. I.e. if there are only 2 partition slots for the selected
partition type, setting this value larger than 2 is without effect, since no more than
2 concurrent versions could be stored in the image anyway.
Added in version 251.
RemoveTemporary=
Takes a boolean argument. If this option is enabled (which is the default) before
initiating an update, all left-over, incomplete updates from a previous attempt are
removed from the target directory. This only has an effect if the target resource
Type= is selected as regular-file, directory or subvolume.
Added in version 251.
CurrentSymlink=
Takes a symlink name as argument. If this option is used, as the last step of the
update a symlink under the specified name is created/updated pointing to the completed
update. This is useful in to provide a stable name always pointing to the newest
version of the resource. This is only supported if the target resource Type= is
selected as regular-file, directory or subvolume.
Added in version 251.
SPECIFIERS
Specifiers may be used in the MinVersion=, ProtectVersion=, Path=, MatchPattern= and
CurrentSymlink= settings. The following expansions are understood:
Table 3. Specifiers available
┌──────────┬──────────────────────────┬──────────────────────────┐
│Specifier │ Meaning │ Details │
├──────────┼──────────────────────────┼──────────────────────────┤
│"%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. │
├──────────┼──────────────────────────┼──────────────────────────┤
│"%A" │ Operating system image │ The operating system │
│ │ version │ image version identifier │
│ │ │ of the running system, │
│ │ │ as read from the │
│ │ │ IMAGE_VERSION= field of │
│ │ │ /etc/os-release. If not │
│ │ │ set, resolves to an │
│ │ │ empty string. See os- │
│ │ │ release(5) for more │
│ │ │ information. │
├──────────┼──────────────────────────┼──────────────────────────┤
│"%b" │ Boot ID │ The boot ID of the │
│ │ │ running system, │
│ │ │ formatted as string. See │
│ │ │ random(4) for more │
│ │ │ information. │
├──────────┼──────────────────────────┼──────────────────────────┤
│"%B" │ Operating system build │ The operating system │
│ │ ID │ 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. │
├──────────┼──────────────────────────┼──────────────────────────┤
│"%M" │ Operating system image │ The operating system │
│ │ identifier │ image identifier of the │
│ │ │ running system, as read │
│ │ │ from the IMAGE_ID= field │
│ │ │ of /etc/os-release. If │
│ │ │ not set, resolves to an │
│ │ │ empty string. See os- │
│ │ │ release(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 │ The operating system │
│ │ ID │ 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 │ The operating system │
│ │ ID │ 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. │
├──────────┼──────────────────────────┼──────────────────────────┤
│"%T" │ Directory for temporary │ This is either /tmp or │
│ │ files │ the path "$TMPDIR", │
│ │ │ "$TEMP" or "$TMP" are │
│ │ │ set to. (Note that the │
│ │ │ directory may be │
│ │ │ specified without a │
│ │ │ trailing slash.) │
├──────────┼──────────────────────────┼──────────────────────────┤
│"%V" │ Directory for larger and │ This is either /var/tmp │
│ │ persistent temporary │ or the path "$TMPDIR", │
│ │ files │ "$TEMP" or "$TMP" are │
│ │ │ set to. (Note that the │
│ │ │ directory may be │
│ │ │ specified without a │
│ │ │ trailing slash.) │
├──────────┼──────────────────────────┼──────────────────────────┤
│"%%" │ Single percent sign │ Use "%%" in place of "%" │
│ │ │ to specify a single │
│ │ │ percent sign. │
└──────────┴──────────────────────────┴──────────────────────────┘
Do not confuse the "%" specifier expansion prefix with the "@" pattern matching wildcard
prefix. The former are simple shortcuts that are expanded while the drop-in files are
parsed, the latter encapsulate a variable part of a match pattern string. For details
about pattern matching wildcards, see above.
EXAMPLES
Example 1. Updates for a Verity Enabled Secure OS
With the following three files we define a root file system partition, a matching Verity
partition, and a unified kernel image to update as one. This example is an extension of
the example discussed earlier in this man page.
# /usr/lib/sysupdate.d/50-verity.conf
[Transfer]
ProtectVersion=%A
[Source]
Type=url-file
Path=https://download.example.com/
MatchPattern=foobarOS_@v_@u.verity.xz
[Target]
Type=partition
Path=auto
MatchPattern=foobarOS_@v_verity
MatchPartitionType=root-verity
PartitionFlags=0
ReadOnly=1
The above defines the update mechanism for the Verity partition of the root file system.
Verity partition images are downloaded from
"https://download.example.com/foobarOS_@v_@u.verity.xz" and written to a suitable local
partition, which is marked read-only. Under the assumption this update is run from the
image itself the current image version (i.e. the "%A" specifier) is marked as protected,
to ensure it is not corrupted while booted. Note that the partition UUID for the target
partition is encoded in the source file name. Fixating the partition UUID can be useful to
ensure that "roothash=" on the kernel command line is sufficient to pinpoint both the
Verity and root file system partition, and also encode the Verity root level hash (under
the assumption the UUID in the file names match their top-level hash, the way systemd-gpt-
auto-generator(8) suggests).
# /usr/lib/sysupdate.d/60-root.conf
[Transfer]
ProtectVersion=%A
[Source]
Type=url-file
Path=https://download.example.com/
MatchPattern=foobarOS_@v_@u.root.xz
[Target]
Type=partition
Path=auto
MatchPattern=foobarOS_@v
MatchPartitionType=root
PartitionFlags=0
ReadOnly=1
The above defines a matching transfer definition for the root file system.
# /usr/lib/sysupdate.d/70-kernel.conf
[Transfer]
ProtectVersion=%A
[Source]
Type=url-file
Path=https://download.example.com/
MatchPattern=foobarOS_@v.efi.xz
[Target]
Type=regular-file
Path=/EFI/Linux
PathRelativeTo=boot
MatchPattern=foobarOS_@v+@l-@d.efi \
foobarOS_@v+@l.efi \
foobarOS_@v.efi
Mode=0444
TriesLeft=3
TriesDone=0
InstancesMax=2
The above installs a unified kernel image into the $BOOT partition, as per Boot Loader
Specification[2] Type #2. This defines three possible patterns for the names of the kernel
images, as per Automatic Boot Assessment[3], and ensures when installing new kernels, they
are set up with 3 tries left. No more than two parallel kernels are kept.
With this setup the web server would serve the following files, for a hypothetical version
7 of the OS:
• SHA256SUMS – The manifest file, containing available files and their SHA256 hashes
• SHA256SUMS.gpg – The detached cryptographic signature for the manifest file
• foobarOS_7_8b8186b1-2b4e-4eb6-ad39-8d4d18d2a8fb.verity.xz – The Verity image for
version 7
• foobarOS_7_f4d1234f-3ebf-47c4-b31d-4052982f9a2f.root.xz – The root file system image
for version 7
• foobarOS_7_efi.xz – The unified kernel image for version 7
For each new OS release a new set of the latter three files would be added, each time with
an updated version. The SHA256SUMS manifest should then be updated accordingly, listing
all files for all versions that shall be offered for download.
Example 2. Updates for Plain Directory Container Image
[Source]
Type=url-tar
Path=https://download.example.com/
MatchPattern=myContainer_@v.tar.gz
[Target]
Type=subvolume
Path=/var/lib/machines
MatchPattern=myContainer_@v
CurrentSymlink=myContainer
On updates this downloads "https://download.example.com/myContainer_@v.tar.gz" and
decompresses/unpacks it to /var/lib/machines/myContainer_@v. After each update a symlink
/var/lib/machines/myContainer is created/updated always pointing to the most recent
update.
SEE ALSO
systemd(1), systemd-sysupdate(8), systemd-repart(8)
NOTES
1. Discoverable Partitions Specification
https://uapi-group.org/specifications/specs/discoverable_partitions_specification
2. Boot Loader Specification
https://uapi-group.org/specifications/specs/boot_loader_specification
3. Automatic Boot Assessment
https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT