SYSTEMD\&.SWAP
Section: systemd.swap (5)
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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:
-
•
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.
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.
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.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)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- AUTOMATIC DEPENDENCIES
-
- Implicit Dependencies
-
- Default Dependencies
-
- FSTAB
-
- OPTIONS
-
- SEE ALSO
-
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Time: 05:39:27 GMT, May 15, 2024