Nohang is a highly configurable daemon for Linux which is able to correctly prevent out of memory (OOM) and keep system responsiveness in low memory conditions.
OOM conditions may cause freezes, livelocks, drop caches and processes to be killed (via sending SIGKILL) instead of trying to terminate them correctly (via sending SIGTERM or takes other corrective action). Some applications may crash if it's impossible to allocate memory.
Here are the statements of some users:
"How do I prevent Linux from freezing when out of memory? Today I (accidentally) ran some program on my Linux box that quickly used a lot of memory. My system froze, became unresponsive and thus I was unable to kill the offender. How can I prevent this in the future? Can't it at least keep a responsive core or something running?"
"With or without swap it still freezes before the OOM killer gets run automatically. This is really a kernel bug that should be fixed (i.e. run OOM killer earlier, before dropping all disk cache). Unfortunately kernel developers and a lot of other folk fail to see the problem. Common suggestions such as disable/enable swap, buy more RAM, run less processes, set limits etc. do not address the underlying problem that the kernel's low memory handling sucks camel's balls."
Also look at Why are low memory conditions handled so badly? (discussion with 480+ posts on r/linux).
- Use of earlyoom. This is a simple and lightweight OOM preventer written in C.
- Use of oomd. This is a userspace OOM killer for linux systems whitten in C++ and developed by Facebook.
- Use of nohang.
SIGKILL
andSIGTERM
as signals that can be sent to the victim- impact on the badness of processes via matching their names, cmdlines and UIDs with regular expressions
- possibility of restarting processes via command like
systemctl restart something
if the process is selected as a victim (or run any other command) - GUI notifications:
- OOM prevention results (displays sended signal and displays PID and name of victim)
- Low memory warnings (displays available memory and name of fattest process)
zram
support (mem_used_total
as a trigger)PSI
support (since Linux 4.20+, using/proc/pressure/memory
andsome avg10
as a trigger)- customizable intensity of monitoring
- convenient configuration with a
wellcommented config file
For basic usage:
Linux
3.14+ (sinceMemAvailable
appeared in/proc/meminfo
)Linux
4.20+ if you want to usePSI
Python
3.3+ (not tested with previous)
To show GUI notifications:
libnotify
(Fedora, Arch Linux) orlibnotify-bin
(Debian GNU/Linux, Ubuntu)sudo
if nohang started with UID=0
- VmRSS is 10 — 14 MiB depending on the settings (about 10 MiB by default)
- CPU usage depends on the level of available memory (the frequency of memory status checks increases as the amount of available memory decreases) and monitoring intensity (can be changed by the user via the config)
Please use the latest release version. Current version may be more unstable.
$ git clone https://github.com/hakavlad/nohang.git
$ cd nohang
Run without installing (low memory warnings may not work; note that processes with UID != your UID will not receive signals if nohang is started as a regular user):
$ ./nohang
To install:
$ sudo make install
To enable and start on systems with systemd:
$ sudo make systemd
To uninstall:
$ sudo make uninstall
For Arch Linux, there's an AUR package. Use your favorite AUR helper.
./nohang -h
usage: nohang [-h] [-c CONFIG]
optional arguments:
-h, --help show this help message and exit
-c CONFIG, --config CONFIG
path to the config file, default values:
./nohang.conf, /etc/nohang/nohang.conf
The program can be configured by editing the config file. The configuration includes the following sections:
- Memory levels to respond to as an OOM threat
- The frequency of checking the level of available memory (and CPU usage)
- The prevention of killing innocent victims
- Impact on the badness of processes via matching their names, cmdlines and UIDs with regular expressions
- The execution of a specific command instead of sending the SIGTERM signal
- GUI notifications:
- results of preventing OOM
- low memory warnings
- Preventing the slowing down of the program
- Output verbosity
Just read the description of the parameters and edit the values. Please restart nohang to apply changes. Default path to the config after installing is /etc/nohang/nohang.conf
.
oom-sort
is an additional diagnostic tool that will be installed with nohang
package. It sorts the processes in descending order of their oom_score
and also displays oom_score_adj
, Uid
, Pid
, Name
, VmRSS
, VmSwap
and optionally cmdline
. Run oom-sort --help
for more info.
Usage:
$ oom-sort
Output like follow:
oom_score oom_score_adj Uid Pid Name VmRSS VmSwap cmdline
--------- ------------- ----- ----- --------------- -------- -------- -------
314 300 1000 991 chromium 84 M 0 M /usr/lib/chromium/chromium --type=renderer --field-trial-handle=868244496792098610,5765419126773948943,131072 --service-pipe-token=14782672631740123203 --lang=ru --user-data-dir=/tmp/tmp.TJ91B6F0zB --disable-client-side-phishing-detection --enable-offline-auto-reload --enable-offline-auto-reload-visible-only --num-raster-threads=1 --service-request-channel-token=14782672631740123203 --renderer-client-id=4 --no-v8-untrusted-code-mitigations --shared-files=v8_context_snapshot_data:100,v8_natives_data:101
307 300 1000 1124 chromium 44 M 0 M /usr/lib/chromium/chromium --type=renderer --field-trial-handle=868244496792098610,5765419126773948943,131072 --service-pipe-token=10276223625123198448 --lang=ru --user-data-dir=/tmp/tmp.TJ91B6F0zB --disable-client-side-phishing-detection --enable-offline-auto-reload --enable-offline-auto-reload-visible-only --num-raster-threads=1 --service-request-channel-token=10276223625123198448 --renderer-client-id=6 --no-v8-untrusted-code-mitigations --shared-files=v8_context_snapshot_data:100,v8_natives_data:101
217 200 1000 962 chromium 99 M 0 M /usr/lib/chromium/chromium --type=gpu-process --field-trial-handle=868244496792098610,5765419126773948943,131072 --user-data-dir=/tmp/tmp.TJ91B6F0zB --disable-breakpad --gpu-preferences=KAAAAAAAAACAAABAAQAAAAAAAAAAAGAAAAAAAAEAAAAIAAAAAAAAAAgAAAAAAAAA --user-data-dir=/tmp/tmp.TJ91B6F0zB --service-request-channel-token=2848128951654484113
202 200 1000 1032 chromium 16 M 0 M /usr/lib/chromium/chromium --type=-broker
43 0 1000 736 firefox-esr 251 M 0 M /usr/lib/firefox-esr/firefox-esr
21 0 1000 914 chromium 124 M 0 M /usr/lib/chromium/chromium --show-component-extension-options --ignore-gpu-blacklist --no-default-browser-check --disable-pings --media-router=0 --enable-remote-extensions --user-data-dir=/tmp/tmp.TJ91B6F0zB
17 0 1000 844 Web Content 103 M 0 M /usr/lib/firefox-esr/plugin-container -greomni /usr/lib/firefox-esr/omni.ja -appomni /usr/lib/firefox-esr/browser/omni.ja -appdir /usr/lib/firefox-esr/browser 736 true tab
16 0 1000 31555 dolphin 95 M 0 M dolphin
15 0 0 863 Xorg 92 M 0 M /usr/lib/xorg/Xorg :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
8 0 110 860 tor 50 M 0 M /usr/bin/tor --defaults-torrc /usr/share/tor/tor-service-defaults-torrc -f /etc/tor/torrc --RunAsDaemon 0
8 0 1000 918 chromium 48 M 0 M /usr/lib/chromium/chromium --type=zygote --user-data-dir=/tmp/tmp.TJ91B6F0zB
7 0 1000 1106 mate-panel 43 M 0 M mate-panel
6 0 1000 1157 wnck-applet 35 M 0 M /usr/lib/mate-panel/wnck-applet
Kthreads, zombies and Pid 1 will not be displayed.
Interactive OOM trigger (not implemented)
To view the latest entries in the log (for systemd users):
$ sudo journalctl -eu nohang
See also man journalctl
.
- Awful documentation
- Slowly starting, slowly looking for a victim, especially when using swapspace
- It is written in an interpreted language and is actually a prototype
Please create issues. Use cases, feature requests and any questions are welcome. See also CoC.
-
In progress
- Improve modifing badness by matching with RE pattern:
- Add suppot matching
cmdline
andUID
with regular expressions - Fix: replace
re.fullmatch()
byre.search()
- Validation RE patterns at startup
- Add suppot matching
- Improve output:
- Display
UID
,oom_score
,oom_score_adj
,VmSize
,RssAnon
,RssFile
,RssShmem
andcmdline
of the victim in corrective action reports - Print in terminal with colors
- Print statistics on corrective actions after each corrective action
- Display
- Optimize limiting
oom_score_adj
: now it can works without UID=0 - Optimize GUI warnings: find env without run
ps
andenv
- Fix conf parsing: use of
line.partition('=')
instead ofline.split('=')
- Add
PSI
support (using/proc/pressure/memory
, need Linux 4.20+) - Add
oom-sort
- Add
oom-trigger
- Adoption of the code of conduct
- Redesign of the config
- Improve modifing badness by matching with RE pattern:
-
v0.1, 2018-11-23
- 1st release