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NAME | SYNOPSIS | DESCRIPTION | SETUP INFORMATION | USAGE RECOMMENDATIONS | 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 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.
The system must be running systemd with a full unified cgroup
hierarchy for the expected cgroups-v2 features. Furthermore,
resource accounting must be turned on for all units monitored by
systemd-oomd. The easiest way to turn on resource accounting is
by ensuring the values for DefaultCPUAccounting,
DefaultIOAccounting, DefaultMemoryAccounting, and
DefaultTasksAccounting are 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.
The system must also have swap enabled for systemd-oomd to
function correctly. 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.
Be aware that if you intend to enable monitoring and actions on
user.slice, user-$UID.slice, or their ancestor cgroups, it is
highly recommended that your programs be managed by the systemd
user manager to prevent running too many processes under the same
session scope (and thus avoid a situation where memory intensive
tasks trigger systemd-oomd to kill everything under the cgroup).
If you're using a desktop environment like GNOME, it already
spawns many session components with the systemd user manager.
ManagedOOMSwap= works with the system-wide swap values, so
setting it on the root slice -.slice, and allowing all descendant
cgroups to be eligible candidates may make the most sense.
ManagedOOMMemoryPressure= tends to work better on the cgroups
below the root slice -.slice. For units which tend to have
processes that are less latency sensitive (e.g. system.slice), a
higher limit like the default of 60% may be acceptable, as those
processes can usually ride out slowdowns caused by lack of memory
without serious consequences. However, something like
user@$UID.service may prefer a much lower value like 40%.
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 2020-12-18. (At that
time, the date of the most recent commit that was found in the
repository was 2020-12-18.) 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 247 SYSTEMD-OOMD.SERVICE(8)
Pages that refer to this page: oomctl(1), oomd.conf(5), org.freedesktop.oom1(5), systemd.resource-control(5), systemd.directives(7), systemd.index(7)
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