The oom-killer generally has a bad reputation among Linux users. This may be part of the reason Linux invokes it only when it has absolutely no other choice. It will swap out the desktop environment, drop the whole page cache and empty every buffer before it will ultimately kill a process. At least that's what I think that it will do. I have yet to be patient enough to wait for it, sitting in front of an unresponsive system.
This made me and other people wonder if the oom-killer could be configured to step in earlier: reddit r/linux, superuser.com, unix.stackexchange.com.
As it turns out, no, it can't. At least using the in-kernel oom-killer. In the user space, however, we can do whatever we want.
earlyoom checks the amount of available memory and free swap up to 10
times a second (less often if there is a lot of free memory).
By default if both are below 10%, it will kill the largest process (highest oom_score
).
The percentage value is configurable via command line
arguments.
In the free -m
output below, the available memory is 2170 MiB and
the free swap is 231 MiB.
total used free shared buff/cache available
Mem: 7842 4523 137 841 3182 2170
Swap: 1023 792 231
Why is "available" memory checked as opposed to "free" memory? On a healthy Linux system, "free" memory is supposed to be close to zero, because Linux uses all available physical memory to cache disk access. These caches can be dropped any time the memory is needed for something else.
The "available" memory accounts for that. It sums up all memory that is unused or can be freed immediately.
Note that you need a recent version of
free
and Linux kernel 3.14+ to see the "available" column. If you have
a recent kernel, but an old version of free
, you can get the value
from grep MemAvailable /proc/meminfo
.
When both your available memory and free swap drop below 10% of the total,
it will send the SIGTERM
signal to the process that uses the most memory in the opinion of
the kernel (/proc/*/oom_score
). It can optionally (-i
option) ignore
any positive adjustments set in /proc/*/oom_score_adj
to protect innocent
victims (see below).
- nohang, a similar project like earlyoom, written in Python and with additional features and configuration options.
- facebooks's pressure stall information (psi) kernel patches and the accompanying oomd userspace helper. The patches are merged in Linux 4.20.
Earlyoom does not use echo f > /proc/sysrq-trigger
because the Chrome people made
their browser (and all electron-based apps - vscode, skype, discord etc) always be
the first (innocent!) victim by setting oom_score_adj
very high.
Instead, earlyoom finds out itself by reading through /proc/*/status
(actually /proc/*/statm
, which contains the same information but is easier to
parse programmatically).
Additionally, in recent kernels (tested on 4.0.5), triggering the kernel oom killer manually may not work at all. That is, it may only free some graphics memory (that will be allocated immediately again) and not actually kill any process. Here you can see how this looks like on my machine (Intel integrated graphics).
About 2 MiB
(VmRSS
), though only 220 kiB
is private memory (RssAnon
).
The rest is the libc library (RssFile
) that is shared with other processes.
All memory is locked using mlockall()
to make sure earlyoom does not slow down in low memory situations.
Compiling yourself is easy:
git clone https://github.com/rfjakob/earlyoom.git
cd earlyoom
make
Optional: Run the integrated self-tests:
make test
Start earlyoom automatically by registering it as a service:
sudo make install # systemd
sudo make install-initscript # non-systemd
Note that for systems with SELinux disabled (Ubuntu 19.04, Debian 9 ...) chcon warnings reporting failure to set the context can be safely ignored.
For Debian 10+ and Ubuntu 18.04+, there's a Debian package:
sudo apt install earlyoom
For Fedora and RHEL 8 with EPEL, there's a Fedora package:
sudo dnf install earlyoom
sudo systemctl enable --now earlyoom
For Arch Linux, there's an Arch Linux package:
sudo pacman -S earlyoom
sudo systemctl enable --now earlyoom
Availability in other distributions: see repology page.
Just start the executable you have just compiled:
./earlyoom
It will inform you how much memory and swap you have, what the minimum is, how much memory is available and how much swap is free.
./earlyoom
earlyoom v1.4-6-ga4021ae
mem total: 9823 MiB, swap total: 9823 MiB
sending SIGTERM when mem <= 10 % and swap <= 10 %,
SIGKILL when mem <= 5 % and swap <= 5 %
Could not lock memory - continuing anyway: Cannot allocate memory
mem avail: 5091 of 9823 MiB (51 %), swap free: 9823 of 9823 MiB (100 %)
mem avail: 5084 of 9823 MiB (51 %), swap free: 9823 of 9823 MiB (100 %)
mem avail: 5086 of 9823 MiB (51 %), swap free: 9823 of 9823 MiB (100 %)
[...]
If the values drop below the minimum, processes are killed until it is above the minimum again. Every action is logged to stderr. If you are running earlyoom as a systemd service, you can view the last 10 lines using
systemctl status earlyoom
Since version 1.6, earlyoom can send notifications about killed processes
via the system d-bus. Pass -n
to enable them.
To actually see the notifications in your GUI session, you need to have systembus-notify running as your user.
The command-line flag --prefer
specifies processes to prefer killing;
likewise, --avoid
specifies
processes to avoid killing. The list of processes is specified by a regex expression.
For instance, to avoid having foo
and bar
be killed:
earlyoom --avoid '^(foo|bar)$'
The regex is matched against the basename of the process as shown
in /proc/PID/stat
.
If you are running earlyoom as a system service (through systemd or init.d), you can adjust its configuration via the file provided in /etc/default/earlyoom
. The file already contains some examples in the comments, which you can use to build your own set of configuration based on the supported command line options, for example:
EARLYOOM_ARGS="-m 5 -r 60 --avoid '(^|/)(init|Xorg|ssh)$' --prefer '(^|/)(java|chromium)$'"
After adjusting the file, simply restart the service to apply the changes. For example, for systemd:
systemctl restart earlyoom
Please note that this configuration file has no effect on earlyoom instances outside of systemd/init.d.
./earlyoom -h
earlyoom v1.6-preview
Usage: ./earlyoom [OPTION]...
-m PERCENT[,KILL_PERCENT] set available memory minimum to PERCENT of total
(default 10 %).
earlyoom sends SIGTERM once below PERCENT, then
SIGKILL once below KILL_PERCENT (default PERCENT/2).
-s PERCENT[,KILL_PERCENT] set free swap minimum to PERCENT of total (default
10 %).
Note: both memory and swap must be below minimum for
earlyoom to act.
-M SIZE[,KILL_SIZE] set available memory minimum to SIZE KiB
-S SIZE[,KILL_SIZE] set free swap minimum to SIZE KiB
-i user-space oom killer should ignore positive
oom_score_adj values
-n enable d-bus notifications
-d enable debugging messages
-v print version information and exit
-r INTERVAL memory report interval in seconds (default 1), set
to 0 to disable completely
-p set niceness of earlyoom to -20 and oom_score_adj to
-100
--prefer REGEX prefer to kill processes matching REGEX
--avoid REGEX avoid killing processes matching REGEX
--dryrun dry run (do not kill any processes)
-h, --help this help text
See the man page for details.
Bug reports and pull requests are welcome via github. In particular, I am glad to accept
- Use case reports and feedback
-
v1.6.2, 2020-10-14
-
1.6.1, 2020-07-07
-
1.6, 2020-04-11
- Replace old
notify-send
GUI notification logic withdbus-send
/ systembus-notify (#183)-n
/-N
now enables the new logic- You need to have systembus-notify running in your GUI session for notifications for work
- Handle
/proc
mounted with hidepid gracefully (issue #184)
- Replace old
-
v1.5, 2020-03-22
-
v1.4, 2020-03-01
- Make victim selection logic 50% faster by lazy-loading process attributes
- Log the user id
uid
of killed processes in addition to pid and name - Color debug log in light grey
- Code clean-up
- Use block-local variables where possible
- Introduce PATH_LEN to replace several hardcoded buffer lengths
- Expand testsuite (
make test
) - Run
cppcheck
when available - Add unit-test benchmarks (
make bench
) - Drop root privileges in systemd unit file
earlyoom.service
-
v1.3.1, 2020-02-27
- Fix spurious testsuite failure on systems with a lot of RAM (issue #156)
-
v1.3, 2019-05-26
- Wait for processes to actually exit when sending a signal
- This fixes the problem that earlyoom sometimes kills more than one process when one would be enough (issue #121)
- Be more liberal in what limits to accepts for SIGTERM and SIGKILL
(issue #97)
- Don't exit with a fatal error if SIGTERM limit < SIGKILL limit
- Allow zero SIGKILL limit
- Reformat startup output to make it clear that BOTH swap and mem must be <= limit
- Add notify_all_users.py helper script
- Add CODE_OF_CONDUCT.md (Contributor Covenant 1.4) (#102)
- Fix possibly truncated UTF8 app names in log output (#110)
- Wait for processes to actually exit when sending a signal
-
v1.2, 2018-10-28
- Implement adaptive sleep time (= adaptive poll rate) to lower CPU usage further (issue #61)
- Remove option to use kernel oom-killer (
-k
, now ignored for compatibility) (issue #80) - Gracefully handle the case of swap being added or removed after earlyoom was started (issue 62, commit)
- Implement staged kill: first SIGTERM, then SIGKILL, with configurable limits (issue #67)
-
v1.1, 2018-07-07
- Fix possible shell code injection through GUI notifications (commit)
- On failure to kill any process, only sleep 1 second instead of 10 (issue #74)
- Send the GUI notification after killing, not before (issue #73)
- Accept
--help
in addition to-h
- Fix wrong process name in log and in kill notification (commit 1, commit 2, issue #52, issue #65, issue #194)
- Fix possible division by zero with
-S
(commit)
-
v1.0, 2018-01-28
- Add
--prefer
and--avoid
options (@TomJohnZ) - Add support for GUI notifications, add options
-n
and-N
- Add
-
v0.12: Add
-M
and-S
options (@nailgun); add man page, parameterize Makefile (@yangfl) -
v0.11: Fix undefined behavoir in get_entry_fatal (missing return, commit)
-
v0.10: Allow to override Makefile's VERSION variable to make packaging easier, add
-v
command-line option -
v0.9: If oom_score of all processes is 0, use VmRss to find a victim
-
v0.8: Use a guesstimate if the kernel does not provide MemAvailable
-
v0.7: Select victim by oom_score instead of VmRSS, add options
-i
and-d
-
v0.6: Add command-line options
-m
,-s
,-k
-
v0.5: Add swap support
-
v0.4: Add SysV init script (thanks @joeytwiddle), use the new
MemAvailable
from/proc/meminfo
(needs Linux 3.14+, commit) -
v0.2: Add systemd unit file
-
v0.1: Initial release