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NAME | SYNOPSIS | DESCRIPTION | AUTOMATIC DEPENDENCIES | FSTAB | OPTIONS | SEE ALSO | COLOPHON |
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SYSTEMD.SWAP(5) systemd.swap SYSTEMD.SWAP(5)
systemd.swap - Swap unit configuration
swap.swap
A unit configuration file whose name ends in ".swap" encodes
information about a swap device or file for memory paging
controlled and supervised by systemd.
This man page lists the configuration options specific to this
unit type. See systemd.unit(5) for the common options of all unit
configuration files. The common configuration items are
configured in the generic [Unit] and [Install] sections. The swap
specific configuration options are configured in the [Swap]
section.
Additional options are listed in systemd.exec(5), which define
the execution environment the swapon(8) program is executed in,
in systemd.kill(5), which define the way these processes are
terminated, and in systemd.resource-control(5), which configure
resource control settings for these processes of the unit.
Swap units must be named after the devices or files they control.
Example: the swap device /dev/sda5 must be configured in a unit
file dev-sda5.swap. For details about the escaping logic used to
convert a file system path to a unit name, see systemd.unit(5).
Note that swap units cannot be templated, nor is possible to add
multiple names to a swap unit by creating additional symlinks to
it.
Note that swap support on Linux is privileged, swap units are
hence only available in the system service manager (and root's
user service manager), but not in unprivileged user's service
manager.
Implicit Dependencies
The following dependencies are implicitly added:
• All swap units automatically get the BindsTo= and After=
dependencies on the device units or the mount units of the
files they are activated from.
Additional implicit dependencies may be added as result of
execution and resource control parameters as documented in
systemd.exec(5) and systemd.resource-control(5).
Default Dependencies
The following dependencies are added unless
DefaultDependencies=no is set:
• Swap units automatically acquire a Conflicts= and a Before=
dependency on umount.target so that they are deactivated at
shutdown as well as a Before=swap.target dependency.
Swap units may either be configured via unit files, or via
/etc/fstab (see fstab(5) for details). Swaps listed in /etc/fstab
will be converted into native units dynamically at boot and when
the configuration of the system manager is reloaded. See
systemd-fstab-generator(8) for details about the conversion.
If a swap device or file is configured in both /etc/fstab and a
unit file, the configuration in the latter takes precedence.
When reading /etc/fstab, a few special options are understood by
systemd which influence how dependencies are created for swap
units.
noauto, auto
With noauto, the swap unit will not be added as a dependency
for swap.target. This means that it will not be activated
automatically during boot, unless it is pulled in by some
other unit. The auto option has the opposite meaning and is
the default.
Added in version 218.
nofail
With nofail, the swap unit will be only wanted, not required
by swap.target. This means that the boot will continue even
if this swap device is not activated successfully.
Added in version 218.
x-systemd.device-timeout=
Configure how long systemd should wait for a device to show
up before giving up on an entry from /etc/fstab. Specify a
time in seconds or explicitly append a unit such as "s",
"min", "h", "ms".
Note that this option can only be used in /etc/fstab, and
will be ignored when part of the Options= setting in a unit
file.
Added in version 215.
x-systemd.makefs
The swap structure will be initialized on the device. If the
device is not "empty", i.e. it contains any signature, the
operation will be skipped. It is hence expected that this
option remains set even after the device has been
initialized.
Note that this option can only be used in /etc/fstab, and
will be ignored when part of the Options= setting in a unit
file.
See systemd-mkswap@.service(8) and the discussion of
wipefs(8) in systemd.mount(5).
Added in version 240.
Swap unit files may include [Unit] and [Install] sections, which
are described in systemd.unit(5).
Swap unit files must include a [Swap] section, which carries
information about the swap device it supervises. A number of
options that may be used in this section are shared with other
unit types. These options are documented in systemd.exec(5),
systemd.kill(5) and systemd.resource-control(5). The options
specific to the [Swap] section of swap units are the following:
What=
Takes an absolute path or a fstab-style identifier of a
device node or file to use for paging. See swapon(8) for
details. If this refers to a device node, a dependency on the
respective device unit is automatically created. (See
systemd.device(5) for more information.) If this refers to a
file, a dependency on the respective mount unit is
automatically created. (See systemd.mount(5) for more
information.) This option is mandatory. Note that the usual
specifier expansion is applied to this setting, literal
percent characters should hence be written as "%%".
Priority=
Swap priority to use when activating the swap device or file.
This takes an integer. This setting is optional and ignored
when the priority is set by pri= in the Options= key.
Options=
May contain an option string for the swap device. This may be
used for controlling discard options among other
functionality, if the swap backing device supports the
discard or trim operation. (See swapon(8) for more
information.) Note that the usual specifier expansion is
applied to this setting, literal percent characters should
hence be written as "%%".
Added in version 217.
TimeoutSec=
Configures the time to wait for the swapon command to finish.
If a command does not exit within the configured time, the
swap will be considered failed and be shut down again. All
commands still running will be terminated forcibly via
SIGTERM, and after another delay of this time with SIGKILL.
(See KillMode= in systemd.kill(5).) Takes a unit-less value
in seconds, or a time span value such as "5min 20s". Pass "0"
to disable the timeout logic. Defaults to
DefaultTimeoutStartSec= from the manager configuration file
(see systemd-system.conf(5)).
Check systemd.unit(5), systemd.exec(5), and systemd.kill(5) for
more settings.
systemd(1), systemctl(1), systemd-system.conf(5),
systemd.unit(5), systemd.exec(5), systemd.kill(5),
systemd.resource-control(5), systemd.device(5), systemd.mount(5),
swapon(8), systemd-fstab-generator(8), systemd.directives(7)
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
man-pages@man7.org
systemd 257~devel SYSTEMD.SWAP(5)
Pages that refer to this page: systemd(1), systemd.exec(5), systemd.kill(5), systemd.resource-control(5), systemd.unit(5), systemd.directives(7), systemd.index(7), systemd.syntax(7), systemd-fstab-generator(8), systemd-gpt-auto-generator(8)
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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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