1SYSTEMD-OOMD.SERVICE(8)      systemd-oomd.service      SYSTEMD-OOMD.SERVICE(8)
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NAME

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

10       systemd-oomd.service
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12       /usr/lib/systemd/systemd-oomd
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DESCRIPTION

15       systemd-oomd is a system service that uses cgroups-v2 and pressure
16       stall information (PSI) to monitor and take action on processes before
17       an OOM occurs in kernel space.
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19       You can enable monitoring and actions on units by setting
20       ManagedOOMSwap= and/or ManagedOOMMemoryPressure= to the appropriate
21       value.  systemd-oomd will periodically poll enabled units' cgroup data
22       to detect when corrective action needs to occur. When an action needs
23       to happen, it will only be performed on the descendant cgroups of the
24       enabled units. More precisely, only cgroups with memory.oom.group set
25       to 1 and leaf cgroup nodes are eligible candidates. Action will be
26       taken recursively on all of the processes under the chosen candidate.
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28       See oomd.conf(5) for more information about the configuration of this
29       service.
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SETUP INFORMATION

32       The system must be running systemd with a full unified cgroup hierarchy
33       for the expected cgroups-v2 features. Furthermore, memory accounting
34       must be turned on for all units monitored by systemd-oomd. The easiest
35       way to turn on memory accounting is by ensuring the value for
36       DefaultMemoryAccounting= is set to true in systemd-system.conf(5).
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38       You will need a kernel compiled with PSI support. This is available in
39       Linux 4.20 and above.
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41       It is highly recommended for the system to have swap enabled for
42       systemd-oomd to function optimally. With swap enabled, the system
43       spends enough time swapping pages to let systemd-oomd react. Without
44       swap, the system enters a livelocked state much more quickly and may
45       prevent systemd-oomd from responding in a reasonable amount of time.
46       See "In defence of swap: common misconceptions"[1] for more details on
47       swap.
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49       Be aware that if you intend to enable monitoring and actions on
50       user.slice, user-$UID.slice, or their ancestor cgroups, it is highly
51       recommended that your programs be managed by the systemd user manager
52       to prevent running too many processes under the same session scope (and
53       thus avoid a situation where memory intensive tasks trigger
54       systemd-oomd to kill everything under the cgroup). If you're using a
55       desktop environment like GNOME, it already spawns many session
56       components with the systemd user manager.
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USAGE RECOMMENDATIONS

59       ManagedOOMSwap= works with the system-wide swap values, so setting it
60       on the root slice -.slice, and allowing all descendant cgroups to be
61       eligible candidates may make the most sense.
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63       ManagedOOMMemoryPressure= tends to work better on the cgroups below the
64       root slice -.slice. For units which tend to have processes that are
65       less latency sensitive (e.g.  system.slice), a higher limit like the
66       default of 60% may be acceptable, as those processes can usually ride
67       out slowdowns caused by lack of memory without serious consequences.
68       However, something like user@$UID.service may prefer a much lower value
69       like 40%.
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SEE ALSO

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

76        1. "In defence of swap: common misconceptions"
77           https://chrisdown.name/2018/01/02/in-defence-of-swap.html
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81systemd 248                                            SYSTEMD-OOMD.SERVICE(8)
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