Provided by: systemd_257.9-0ubuntu2_amd64 
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)