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.
For basic usage
- Linux (>= 3.14, since MemAvailable appeared in /proc/meminfo)
- Python (>= 3.3)
To respond to PSI metrics (optional)
- Linux (>= 4.20) with CONFIG_PSI=y
To show GUI notifications (optional)
- notification server (most of desktop environments use their own implementations)
- libnotify (Arch Linux, Fedora, openSUSE) or libnotify-bin (Debian GNU/Linux, Ubuntu)
- sudo if nohang started with UID=0.
show this help message and exit
show version of installed package and exit
consume memory until 40 MiB (MemAvailable + SwapFree) remain free, and terminate the process
-c CONFIG, --config CONFIG
path to the config file. This should only be used with one of the following options: --monitor, --tasks, --check
check and show the configuration and exit. This should only be used with -c/--config CONFIG option
start monitoring. This should only be used with -c/--config CONFIG option
show tasks state and exit. This should only be used with -c/--config CONFIG option
path to vanilla nohang configuration file
path to configuration file with settings optimized for desktop usage
optional log file that stores entries if separate_log=True in the config
logrotate config file that controls rotation in /var/log/nohang/
nohang.conf vs nohang-desktop.conf
- nohang.conf provides vanilla default settings without PSI checking enabled, without any badness correction and without GUI notifications enabled.
- nohang-desktop.conf provides default settings optimized for desktop usage.
The next problems can occur with out-of-tree kernels and modules:
- The ZFS ARC cache is memory-reclaimable, like the Linux buffer cache. However, in contrast to the buffer cache, it currently does not count to MemAvailable . See also  and .
- Linux kernels without CONFIG_CGROUP_CPUACCT=y (linux-ck, for example) provide incorrect PSI metrics, see this thread .
How to Configure
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
- Response on PSI memory metrics
- 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 or sending any signal instead of sending the SIGTERM signal
- notifications of corrective actions taken
- low memory warnings
Just read the description of the parameters and edit the values. Restart the daemon to apply the changes.
Check the config for errors:
$ nohang --check --config /path/to/config
How to Test
The safest way is to run nohang --memload. This causes memory consumption, and the process will exits before OOM occurs. Another way is to run tail /dev/zero. This causes fast memory comsumption and causes OOM at the end. If testing occurs while nohang is running, these processes should be terminated before OOM occurs.
To view the latest entries in the log (for systemd users):
$ sudo journalctl -eu nohang.service
$ sudo journalctl -eu nohang-desktop.service
You can also enable separate_log in the config to logging in /var/log/nohang/nohang.log.
Sending SIGTERM, SIGINT, SIGQUIT or SIGHUP signals to the nohang process causes it displays corrective action stats and exits.
Please ask any questions and report bugs at <https://github.com/hakavlad/nohang/issues>.
Written by Alexey Avramov <firstname.lastname@example.org>.
Homepage is <https://github.com/hakavlad/nohang>.
oom-sort(1), psi-top(1), psi2log(1)
oom-sort(1), psi2log(1), psi-top(1).