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.
AUTOMATIC DEPENDENCIES
Implicit Dependencies
The following dependencies are implicitly added:
o 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:
o 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.
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.
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.
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).
OPTIONS
Swap 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) and systemd.kill(5). The options
specific to the [Swap] section of swap units are the following:
What=
Takes an absolute path 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 "%%".
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.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 245 SYSTEMD.SWAP(5)