SYSTEMD.SWAP(5) systemd.swap SYSTEMD.SWAP(5)
NAME
systemd.swap - Swap unit configuration
SYNOPSIS
swap.swap
DESCRIPTION
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.
AUTOMATIC DEPENDENCIES
Implicit Dependencies
The following dependencies are implicitly added:
• All swap units automatically get the Requires= 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.
FSTAB
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.
OPTIONS
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.
SEE ALSO
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)
systemd 257.9 SYSTEMD.SWAP(5)
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