systemd-oomd.service(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | SETUP INFORMATION | USAGE RECOMMENDATIONS | SEE ALSO | NOTES | COLOPHON

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

NAME         top

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

SYNOPSIS         top

       systemd-oomd.service

       /usr/lib/systemd/systemd-oomd

DESCRIPTION         top

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

       You can enable monitoring and actions on units by setting
       ManagedOOMSwap= and/or ManagedOOMMemoryPressure= to the
       appropriate value.  systemd-oomd will periodically poll enabled
       units' cgroup data to detect when corrective action needs to
       occur. When an action needs to happen, it will only be performed
       on the descendant cgroups of the enabled units. More precisely,
       only cgroups with memory.oom.group set to 1 and leaf cgroup nodes
       are eligible candidates. Action will be taken recursively on all
       of the processes under the chosen candidate.

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

SETUP INFORMATION         top

       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).

       You will need a kernel 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 a system
       without swap, 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, it already
       spawns many session components with the systemd user manager.

USAGE RECOMMENDATIONS         top

       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 -.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%.

SEE ALSO         top

       systemd(1), systemd-system.conf(5), systemd.resource-control(5),
       oomd.conf(5), oomctl(1)

NOTES         top

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

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 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-27.)  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 249                                      SYSTEMD-OOMD.SERVICE(8)

Pages that refer to this page: oomctl(1)oomd.conf(5)org.freedesktop.oom1(5)systemd.resource-control(5)