SYSTEMD-OOMD.SERVICE(8)	     systemd-oomd.service      SYSTEMD-OOMD.SERVICE(8)

NAME
       systemd-oomd.service, systemd-oomd - A userspace out-of-memory (OOM)
       killer

SYNOPSIS
       systemd-oomd.service

       /usr/lib/systemd/systemd-oomd

DESCRIPTION
       systemd-oomd is a system service that uses cgroups-v2 and pressure
       stall information (PSI) to monitor and take corrective action before an
       OOM occurs in the kernel space.

       You can enable monitoring and actions on units by setting
       ManagedOOMSwap= and ManagedOOMMemoryPressure= in the unit
       configuration, see systemd.resource-control(5).	systemd-oomd retrieves
       information about such units from systemd(1) when it starts and watches
       for subsequent changes.

       Cgroups of units with ManagedOOMSwap= or ManagedOOMMemoryPressure= set
       to kill will be monitored.  systemd-oomd periodically polls PSI
       statistics for the system and those cgroups to decide when to take
       action. If the configured limits are exceeded, systemd-oomd will select
       a cgroup to terminate, and send SIGKILL to all processes in it. Note
       that only descendant cgroups are eligible candidates for killing; the
       unit with its property set to kill is not a candidate (unless one of
       its ancestors set their property to kill). Also only leaf cgroups and
       cgroups with memory.oom.group set to 1 are eligible candidates; see
       OOMPolicy= in systemd.service(5).

       oomctl(1) can be used to list monitored cgroups and pressure
       information.

       See oomd.conf(5) for more information about the configuration of this
       service.

       See org.freedesktop.oom1(5) and org.freedesktop.LogControl1(5) for a
       description of the D-Bus API.

SYSTEM REQUIREMENTS AND CONFIGURATION
       The system must be running systemd with a full unified cgroup hierarchy
       for the expected cgroups-v2 features. Furthermore, memory accounting
       must be turned on for all units monitored by systemd-oomd. The easiest
       way to turn on memory accounting is by ensuring the value for
       DefaultMemoryAccounting= is set to true in systemd-system.conf(5).

       The kernel must be compiled with PSI support. This is available in
       Linux 4.20 and above.

       It is highly recommended for the system to have swap enabled for
       systemd-oomd to function optimally. With swap enabled, the system
       spends enough time swapping pages to let systemd-oomd react. Without
       swap, the system enters a livelocked state much more quickly and may
       prevent systemd-oomd from responding in a reasonable amount of time.
       See "In defence of swap: common misconceptions"[1] for more details on
       swap. Any swap-based actions on systems without swap will be ignored.
       While systemd-oomd can perform pressure-based actions on such a system,
       the pressure increases will be more abrupt and may require more tuning
       to get the desired thresholds and behavior.

       Be aware that if you intend to enable monitoring and actions on
       user.slice, user-$UID.slice, or their ancestor cgroups, it is highly
       recommended that your programs be managed by the systemd user manager
       to prevent running too many processes under the same session scope (and
       thus avoid a situation where memory intensive tasks trigger
       systemd-oomd to kill everything under the cgroup). If you're using a
       desktop environment like GNOME or KDE, it already spawns many session
       components with the systemd user manager.

USAGE RECOMMENDATIONS
       ManagedOOMSwap= works with the system-wide swap values, so setting it
       on the root slice -.slice, and allowing all descendant cgroups to be
       eligible candidates may make the most sense.

       ManagedOOMMemoryPressure= tends to work better on the cgroups below the
       root slice. For units which tend to have processes that are less
       latency sensitive (e.g.	system.slice), a higher limit like the default
       of 60% may be acceptable, as those processes can usually ride out
       slowdowns caused by lack of memory without serious consequences.
       However, something like user@$UID.service may prefer a much lower value
       like 40%.

OPTIONS
       --dry-run
	   Do a dry run of systemd-oomd: when a kill is triggered, print it to
	   the log instead of killing the cgroup.

	   Added in version 253.

       -h, --help
	   Print a short help text and exit.

       --version
	   Print a short version string and exit.

SIGNALS
       SIGHUP
	   Upon reception of the SIGHUP process signal systemd-oomd will
	   reload its configuration file.

	   Added in version 258.

SEE ALSO
       systemd(1), systemd-system.conf(5), systemd.resource-control(5),
       oomd.conf(5), oomctl(1), org.freedesktop.oom1(5)

NOTES
	1. "In defence of swap: common misconceptions"
	   https://chrisdown.name/2018/01/02/in-defence-of-swap.html

systemd 258					       SYSTEMD-OOMD.SERVICE(8)