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

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.

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.

SEE ALSO

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

NOTES

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

COLOPHON

       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 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  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 257~devel                                SYSTEMD-OOMD.SERVICE(8)

Pages that refer to this page: oomctl(1), oomd.conf(5), org.freedesktop.oom1(5), systemd.resource-control(5), systemd.scope(5), systemd.service(5), systemd.directives(7), systemd.index(7)

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