systemd.swap

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 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.

       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 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) 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 247                                                      SYSTEMD.SWAP(5)