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NAME | SYNOPSIS | DESCRIPTION | SYSTEM REQUIREMENTS AND CONFIGURATION | USAGE RECOMMENDATIONS | OPTIONS | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD-OOMD.SERVICE(8) systemd-oomd.service SYSTEMD-OOMD.SERVICE(8)
systemd-oomd.service, systemd-oomd - A userspace out-of-memory
(OOM) killer
systemd-oomd.service
/usr/lib/systemd/systemd-oomd
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.
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-$UID.slice, or their ancestor cgroups, it is
highly recommended that your programs be managed by the systemd
user manager to prevent running too many processes under the same
session scope (and thus avoid a situation where memory intensive
tasks trigger systemd-oomd to kill everything under the cgroup).
If you're using a desktop environment like GNOME or KDE, it
already spawns many session components with the systemd user
manager.
ManagedOOMSwap= works with the system-wide swap values, so
setting it on the root slice -.slice, and allowing all descendant
cgroups to be eligible candidates may make the most sense.
ManagedOOMMemoryPressure= tends to work better on the cgroups
below the root slice. For units which tend to have processes that
are less latency sensitive (e.g. system.slice), a higher limit
like the default of 60% may be acceptable, as those processes can
usually ride out slowdowns caused by lack of memory without
serious consequences. However, something like user@$UID.service
may prefer a much lower value like 40%.
--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.
systemd(1), systemd-system.conf(5), systemd.resource-control(5),
oomd.conf(5), oomctl(1)
1. "In defence of swap: common misconceptions"
https://chrisdown.name/2018/01/02/in-defence-of-swap.html
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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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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