earlyoom
v1.8.2
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 wants to be simple and solid. It is written in pure C with no dependencies. An extensive test suite (unit- and integration tests) is written in Go.
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 memory available
to userspace processes (=total-shared),
it will send the SIGTERM signal to the process that uses the most memory in the opinion of
the kernel (/proc/*/oom_score).
earlyoom does not use echo f > /proc/sysrq-trigger because:
In some kernel versions (tested on v4.0.5), triggering the kernel oom killer manually does 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).
This problem has been fixed in Linux v5.17 (commit f530243a) .
Like the Linux kernel would, earlyoom finds its victim by reading through /proc/*/oom_score.
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
makeOptional: Run the integrated self-tests:
make testStart earlyoom automatically by registering it as a service:
sudo make install # systemd
sudo make install-initscript # non-systemdNote 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 earlyoomFor Fedora and RHEL 8 with EPEL, there's a Fedora package:
sudo dnf install earlyoom
sudo systemctl enable --now earlyoomFor Arch Linux, there's an Arch Linux package:
sudo pacman -S earlyoom
sudo systemctl enable --now earlyoomAvailability in other distributions: see repology page.
Just start the executable you have just compiled:
./earlyoomIt 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
eearlyoom v1.8
mem total: 23890 MiB, user mem total: 21701 MiB, swap total: 8191 MiB
sending SIGTERM when mem avail <= 10.00% and swap free <= 10.00%,
SIGKILL when mem avail <= 5.00% and swap free <= 5.00%
mem avail: 20012 of 21701 MiB (92.22%), swap free: 5251 of 8191 MiB (64.11%)
mem avail: 20031 of 21721 MiB (92.22%), swap free: 5251 of 8191 MiB (64.11%)
mem avail: 20033 of 21723 MiB (92.22%), swap free: 5251 of 8191 MiB (64.11%)
[...]
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 earlyoomIn order to see earlyoom in action, create/simulate a memory leak and let earlyoom do what it does:
tail /dev/zero
If you need any further actions after a process is killed by earlyoom (such as sending emails), you can parse the logs by:
sudo journalctl -u earlyoom | grep sending
Example output for above test command (tail /dev/zero) will look like:
Feb 20 10:59:34 debian earlyoom[10231]: sending SIGTERM to process 7378 uid 1000 "tail": oom_score 156, VmRSS 4962 MiB
For older versions of
earlyoom, use:sudo journalctl -u earlyoom | grep -iE "(sending|killing)"
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.
Additionally, earlyoom can execute a script for each process killed, providing
information about the process via the EARLYOOM_PID, EARLYOOM_UID and
EARLYOOM_NAME environment variables. Pass -N /path/to/script to enable.
Warning: In case of dryrun mode, the script will be executed in rapid succession, ensure you have some sort of rate-limit implemented.
The command-line flag --prefer specifies processes to prefer killing;
likewise, --avoid specifies
processes to avoid killing. See https://github.com/rfjakob/earlyoom/blob/master/MANPAGE.md#--prefer-regex for details.
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 earlyoomPlease note that this configuration file has no effect on earlyoom instances outside of systemd/init.d.
earlyoom v1.8
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
-n enable d-bus notifications
-N /PATH/TO/SCRIPT call script after oom kill
-g kill all processes within a process group
-d, --debug 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
--ignore-root-user do not kill processes owned by root
--sort-by-rss find process with the largest rss (default oom_score)
--prefer REGEX prefer to kill processes matching REGEX
--avoid REGEX avoid killing processes matching REGEX
--ignore REGEX ignore processes matching REGEX
--dryrun dry run (do not kill any processes)
--syslog use syslog instead of std streams
-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
v1.8.2, 2024-05-07
earlyoom.service systemd unit file
process_mrelease to allowed syscalls (commit)IPAddressDeny syntax (commit)-p (commit)v1.8.1, 2024-04-17
v1.8, 2024-04-15
user mem total / meminfo_t.UserMemTotal and calculate MemAvailablePercent based on it
(commit,
more info in man page)process_mrelease (#266)NO_COLOR (https://no-color.org/)--sort-by-rss, thanks @RanHuang! This will select a process to kill acc. to the largest RSS
instead of largest oom_score.v1.7, 2022-03-05
-N flag to run a script every time a process is killed (commit,
man page section)-g flag to kill whole process group (#247)-i flag (ignored for compatibility), it does
not work properly on Linux kernels 5.9+ (#234)v1.6.2, 2020-10-14
1.6.1, 2020-07-07
1.6, 2020-04-11
notify-send GUI notification logic with
dbus-send / systembus-notify
(#183)
-n/-N now enables the new logic/proc mounted with
hidepid
gracefully (issue #184)v1.5, 2020-03-22
-p: set oom_score_adj to -100 instead of -1000
(#170)-M and -m, and -S and -s. The
lower value (converted to percentages) will be used.earlyoom.default to 1 hour
instead of 1 minute (#177)v1.4, 2020-03-01
uid of killed processes in addition to pid and namemake test)cppcheck when availablemake bench)earlyoom.servicev1.3.1, 2020-02-27
v1.3, 2019-05-26
v1.2, 2018-10-28
-k, now ignored for compatibility)
(issue #80)v1.1, 2018-07-07
--help in addition to -h-S
(commit)v1.0, 2018-01-28
--prefer and --avoid options (@TomJohnZ)-n and -Nv0.12: Add -M and -S options (@nailgun); add man page, parameterize Makefile (@yangfl)
v0.11: Fix undefined behavior 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
