|
HTML rendering created 2026-05-24 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. |
|
|
NAME | SYNOPSIS | DESCRIPTION | CONFIGURATION DIRECTORIES AND PRECEDENCE | PREKILL EVENT | OOM RULESETS | [OOM] SECTION OPTIONS | SEE ALSO | NOTES | COLOPHON |
|
|
|
OOMD.CONF(5) oomd.conf OOMD.CONF(5)
oomd.conf, oomd.conf.d - Global systemd-oomd configuration files
/etc/systemd/oomd.conf
/run/systemd/oomd.conf
/usr/local/lib/systemd/oomd.conf
/usr/lib/systemd/oomd.conf
/etc/systemd/oomd.conf.d/*.conf
/run/systemd/oomd.conf.d/*.conf
/usr/local/lib/systemd/oomd.conf.d/*.conf
/usr/lib/systemd/oomd.conf.d/*.conf
These files configure the various parameters of the systemd(1)
userspace out-of-memory (OOM) killer, systemd-oomd.service(8). See
systemd.syntax(7) for a general description of the syntax.
The default configuration is set during compilation, so
configuration is only needed when it is necessary to deviate from
those defaults. The main configuration file is loaded from one of
the listed directories in order of priority, only the first file
found is used: /etc/systemd/, /run/systemd/,
/usr/local/lib/systemd/ [1], /usr/lib/systemd/. The vendor version
of the file contains commented out entries showing the defaults as
a guide to the administrator. Local overrides can also be created
by creating drop-ins, as described below. The main configuration
file can also be edited for this purpose (or a copy in /etc/ if it
is shipped under /usr/), however using drop-ins for local
configuration is recommended over modifications to the main
configuration file.
In addition to the main configuration file, drop-in configuration
snippets are read from /usr/lib/systemd/*.conf.d/,
/usr/local/lib/systemd/*.conf.d/, and /etc/systemd/*.conf.d/.
Those drop-ins have higher precedence and override the main
configuration file. Files in the *.conf.d/ configuration
subdirectories are sorted by their filename in lexicographic
order, regardless of in which of the subdirectories they reside.
When multiple files specify the same option, for options which
accept just a single value, the entry in the file sorted last
takes precedence, and for options which accept a list of values,
entries are collected as they occur in the sorted files.
When packages need to customize the configuration, they can
install drop-ins under /usr/. Files in /etc/ are reserved for the
local administrator, who may use this logic to override the
configuration files installed by vendor packages. Drop-ins have to
be used to override package drop-ins, since the main configuration
file has lower precedence. It is recommended to prefix all
filenames in those subdirectories with a two-digit number and a
dash, to simplify the ordering. This also defines a concept of
drop-in priorities to allow OS vendors to ship drop-ins within a
specific range lower than the range used by users. This should
lower the risk of package drop-ins overriding accidentally
drop-ins defined by users. It is recommended to use the range
10-40 for drop-ins in /usr/ and the range 60-90 for drop-ins in
/etc/ and /run/, to make sure that local and transient drop-ins
take priority over drop-ins shipped by the OS vendor.
To disable a configuration file supplied by the vendor, the
recommended way is to place a symlink to /dev/null in the
configuration directory in /etc/, with the same filename as the
vendor configuration file.
systemd-oomd supports notifying external components before killing
a control group. This is done by sending a notification over
varlink to all sockets found in /run/systemd/oomd.prekill.hook/
folder. Each socket should implement the io.systemd.oom.Prekill
interface. The notification contains the control group path to
allow the hook to identify which control group is being killed.
This allows external components to perform any necessary cleanup
or logging before the control group is terminated. The hook is not
intended as a way to avoid the kill, but rather as a notification
mechanism. Note that this is a privileged option as, even if it
has a timeout, is synchronous and delays the kill, so use with
care. The typically preferable mechanism to process memory
pressure is to do what Resource Pressure Handling[2] describes
which is unprivileged, asynchronous and does not delay the kill.
systemd-oomd supports custom rulesets that define conditions and
actions for OOM handling on a per-unit basis. Ruleset files use
the .oomrule extension and are loaded from
/etc/systemd/oomd/rules.d/, /run/systemd/oomd/rules.d/,
/usr/local/lib/systemd/oomd/rules.d/, and
/usr/lib/systemd/oomd/rules.d/. Units opt into rulesets via the
OOMRules= setting in systemd.resource-control(5), which takes a
space-separated list of ruleset names (the file name without the
.oomrule extension).
Each ruleset file contains a "[Rule]" section with the following
options. At least one of MemoryPressureAbove= or SwapUsageMax=
must be configured; rulesets with no conditions are ignored. If
both are set, the conditions are combined with AND, i.e. the
action is only triggered when both thresholds are exceeded
simultaneously.
MemoryPressureAbove=
Sets the memory pressure threshold above which the rule's
action will be triggered. The memory pressure represents the
fraction of time in a 10 second window in which all tasks in
the control group were delayed (PSI "full avg10"). Takes a
value specified in percent (when suffixed with "%"), permille
("‰") or permyriad ("‱"), between 0% and 100%, inclusive. If
unset, this condition is not evaluated. A value of "100%" can
never be exceeded and is therefore rejected with a warning; a
value of "0%" makes the condition true on any observed
pressure, which is usually not useful.
Added in version 261.
SwapUsageMax=
Sets the system-wide swap usage threshold above which the
rule's action will be triggered. Takes a value specified in
percent (when suffixed with "%"), permille ("‰") or permyriad
("‱"), between 0% and 100%, inclusive. If unset, this
condition is not evaluated. A value of "100%" can never be
exceeded and is therefore rejected with a warning; a value of
"0%" fires as soon as any swap is in use, which is usually not
useful.
Added in version 261.
Action=
Specifies the action to take when the rule's conditions are
met. Takes one of "kill-all", "kill-by-pgscan", or
"kill-by-swap". This setting is mandatory; rulesets without
Action= are ignored.
• "kill-all" sends SIGKILL to every process in the unit's
cgroup hierarchy, including any descendant cgroups.
• "kill-by-pgscan" selects and kills the descendant cgroup
with the highest recent page scan (reclaim) rate.
• "kill-by-swap" selects and kills the descendant cgroup
with the highest swap usage.
Added in version 261.
LastingSec=
Sets the duration the conditions must be continuously met
before the action is taken. Takes a time span value, see
systemd.time(7) for details on the permitted syntax. Defaults
to 0, i.e. the action is taken immediately when the conditions
are met.
Added in version 261.
The following options are available in the [OOM] section:
SwapUsedLimit=
Sets the limit for memory and swap usage on the system before
systemd-oomd will take action. If the fraction of memory used
and the fraction of swap used on the system are both more than
what is defined here, systemd-oomd will act on eligible
descendant control groups with swap usage greater than 5% of
total swap, starting from the ones with the highest swap
usage. Which control groups are monitored and what action gets
taken depends on what the unit has configured for
ManagedOOMSwap=. Takes a value specified in percent (when
suffixed with "%"), permille ("‰") or permyriad ("‱"), between
0% and 100%, inclusive. Defaults to 90%.
Added in version 247.
DefaultMemoryPressureLimit=
Sets the limit for memory pressure on the unit's control group
before systemd-oomd will take action. A unit can override this
value with ManagedOOMMemoryPressureLimit=. The memory pressure
for this property represents the fraction of time in a 10
second window in which all tasks in the control group were
delayed. For each monitored control group, if the memory
pressure on that control group exceeds the limit set for
longer than the duration set by
DefaultMemoryPressureDurationSec=, systemd-oomd will act on
eligible descendant control groups, starting from the ones
with the most reclaim activity to the least reclaim activity.
Which control groups are monitored and what action gets taken
depends on what the unit has configured for
ManagedOOMMemoryPressure=. Takes a fraction specified in the
same way as SwapUsedLimit= above. Defaults to 60%.
Added in version 247.
DefaultMemoryPressureDurationSec=
Sets the amount of time a unit's control group needs to have
exceeded memory pressure limits before systemd-oomd will take
action. A unit can override this value with
ManagedOOMMemoryPressureDurationSec=. Memory pressure limits
are defined by DefaultMemoryPressureLimit= and
ManagedOOMMemoryPressureLimit=. Must be set to 0, or at least
1 second. Defaults to 30 seconds when unset or 0.
Added in version 248.
PrekillHookTimeoutSec=
Sets the amount of time systemd-oomd will wait for pre-kill
hooks to complete, before proceeding with the control group
termination. Pre-kill hooks work by placing varlink socket to
/run/systemd/oomd.prekill.hook/ folder. Each socket should
implement interface for notification to work. systemd-oomd
sends a notification before killing a control group for each
discovered socket. The timeout is intended to be global and
not per hook. If all hooks return earlier, the kill is
performed as soon as possible. The timeout must be at least
1s. Defaults to 0, which means systemd-oomd will not wait and
no notifications will be sent.
Added in version 260.
systemd(1), systemd.resource-control(5), systemd-oomd.service(8),
oomctl(1)
1. 💣💥🧨💥💥💣 Please note that those configuration files must
be available at all times. If /usr/local/ is a separate
partition, it may not be available during early boot, and must
not be used for configuration.
2. Resource Pressure Handling
https://systemd.io/PRESSURE
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 2026-05-24. (At that
time, the date of the most recent commit that was found in the
repository was 2026-05-24.) 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 261~rc1 OOMD.CONF(5)
Pages that refer to this page: oomctl(1), systemd.resource-control(5), systemd.directives(7), systemd.index(7), systemd-oomd.service(8)
|
HTML rendering created 2026-05-24 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. |
|