systemd.swap(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | AUTOMATIC DEPENDENCIES | FSTAB | OPTIONS | SEE ALSO | COLOPHON

SYSTEMD.SWAP(5)               systemd.swap               SYSTEMD.SWAP(5)

NAME         top

       systemd.swap - Swap unit configuration

SYNOPSIS         top

       swap.swap

DESCRIPTION         top

       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         top

   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         top

       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         top

       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         top

       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)

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2021-04-01.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-04-01.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 248                                              SYSTEMD.SWAP(5)

Pages that refer to this page: systemd(1)systemd.exec(5)systemd.kill(5)systemd.resource-control(5)systemd.unit(5)systemd.directives(7)systemd.index(7)systemd.syntax(7)systemd-fstab-generator(8)systemd-gpt-auto-generator(8)