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NAME | DESCRIPTION | FILTERING AND SORTING | EXAMPLE | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD.V(7) systemd.v SYSTEMD.V(7)
systemd.v - Directory with Versioned Resources
In various places systemd components accept paths whose trailing
components have the ".v/" suffix, pointing to a directory. These
components will then automatically look for suitable files inside
the directory, do a version comparison and open the newest file
found (by version). Available since version v256. Specifically,
two expressions are supported:
• When looking for files with a suffix .SUFFIX, and a path
...PATH/NAME.SUFFIX.v/ is specified, then all files
...PATH/NAME.SUFFIX.v/NAME_*.SUFFIX are enumerated, filtered,
sorted and the newest file used. The primary sorting key is
the variable part, here indicated by the wildcard "*".
• When a path ...PATH.v/NAME___.SUFFIX is specified (i.e. the
penultimate component of the path ends in ".v" and the final
component contains a triple underscore), then all files
...PATH.v/NAME_*.SUFFIX are enumerated, filtered, sorted and
the newest file used (again, by the variable part, here
indicated by the wildcard "*").
To illustrate this in an example, consider a directory
/var/lib/machines/mymachine.raw.v/, which is populated with three
files:
• mymachine_7.5.13.raw
• mymachine_7.5.14.raw
• mymachine_7.6.0.raw
Invoke a tool such as systemd-nspawn(1) with a command line like
the following:
# systemd-nspawn --image=/var/lib/machines/mymachine.raw.v --boot
Then this would automatically be resolved to the equivalent of:
# systemd-nspawn --image=/var/lib/machines/mymachine.raw.v/mymachine_7.6.0.raw --boot
Much of systemd's functionality that expects a path to a disk
image or OS directory hierarchy support the ".v/" versioned
directory mechanism, for example systemd-nspawn(1),
systemd-dissect(1) or the RootDirectory=/RootImage= settings of
service files (see systemd.exec(5)).
Use the systemd-vpick(1) tool to resolve ".v/" paths from the
command line, for example for usage in shell scripts.
The variable part of the filenames in the ".v/" directories are
filtered and compared primarily with a version comparison,
implementing Version Format Specification[1]. However, additional
rules apply:
• If the variable part is suffixed by one or two integer values
("tries left" and "tries done") in the formats +LEFT or
+LEFT-DONE, then these indicate usage attempt counters. The
idea is that each time before a file is attempted to be used,
its "tries left" counter is decreased, and the "tries done"
counter increased (simply by renaming the file). When the
file is successfully used (which for example could mean for
an OS image: successfully booted) the counters are removed
from the file name, indicating that the file has been
validated to work correctly. This mechanism mirrors the boot
assessment counters defined by Automatic Boot Assessment[2].
Any filenames with no boot counters or with a non-zero "tries
left" counter are sorted before filenames with a zero "tries
left" counter.
• Preceding the use counters (if they are specified), an
optional CPU architecture identifier may be specified in the
filename (separated from the version with an underscore), as
defined in the architecture vocabulary of the
ConditionArchitecture= unit file setting, as documented in
systemd.unit(5). Files whose name indicates an architecture
not supported locally are filtered and not considered for the
version comparison.
• The rest of the variable part is the version string.
Or in other words, the files in the ".v/" directories should
follow one of these naming structures:
• NAME_VERSION.SUFFIX
• NAME_VERSION_ARCHITECTURE.SUFFIX
• NAME_VERSION+LEFT.SUFFIX
• NAME_VERSION+LEFT-DONE.SUFFIX
• NAME_VERSION_ARCHITECTURE+LEFT.SUFFIX
• NAME_VERSION_ARCHITECTURE+LEFT-DONE.SUFFIX
Here's a more comprehensive example, further extending the one
described above. Consider a directory
/var/lib/machines/mymachine.raw.v/, which is populated with the
following files:
• mymachine_7.5.13.raw
• mymachine_7.5.14_x86-64.raw
• mymachine_7.6.0_arm64.raw
• mymachine_7.7.0_x86-64+0-5.raw
Now invoke the following command on an x86-64 machine:
$ systemd-vpick --suffix=.raw /var/lib/machines/mymachine.raw.v/
This would resolve the specified path to
/var/lib/machines/mymachine.raw.v/mymachine_7.5.14_x86-64.raw.
Explanation: even though mymachine_7.7.0_x86-64+0-5.raw has the
newest version, it is not preferred because its tries left
counter is zero. And even though mymachine_7.6.0_arm64.raw has
the second newest version it is also not considered, in this case
because we operate on an x86_64 system and the image is intended
for arm64 CPUs. Finally, the mymachine_7.5.13.raw image is not
considered because it is older than mymachine_7.5.14_x86-64.raw.
systemd(1), systemd-vpick(1), systemd-nspawn(1),
systemd-dissect(1), systemd.exec(5), systemd-sysupdate(1)
1. Version Format Specification
https://uapi-group.org/specifications/specs/version_format_specification/
2. Automatic Boot Assessment
https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT/
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel SYSTEMD.V(7)
Pages that refer to this page: portablectl(1), systemd-dissect(1), systemd-nspawn(1), systemd-vpick(1), org.freedesktop.portable1(5), systemd.exec(5), systemd.directives(7), systemd.index(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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