NAME

       nohang - A sophisticated low memory handler

SYNOPSIS

       nohang [OPTION]...

DESCRIPTION

       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.

REQUIREMENTS

   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.

COMMAND-LINE OPTIONS

   -h, --help
       show this help message and exit

   -v, --version
       show version of installed package and exit

   -m, --memload
       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
       check and show the configuration and exit.  This should only be used with -c/--config CONFIG option

   --monitor
       start monitoring.  This should only be used with -c/--config CONFIG option

   --tasks
       show tasks state and exit.  This should only be used with -c/--config CONFIG option

FILES

   /etc/nohang/nohang.conf
       path to vanilla nohang configuration file

   /etc/nohang/nohang-desktop.conf
       path to configuration file with settings optimized for desktop usage

   /usr/share/nohang/nohang.conf
       path to file with default nohang.conf values

   /usr/share/nohang/nohang-desktop.conf
       path to file with default nohang-desktop.conf values

   /var/log/nohang/nohang.log
       optional log file that stores entries if separate_log=True in the config

   /etc/logrotate.d/nohang
       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 correc‐
         tion and without GUI notifications enabled.

       • nohang-desktop.conf provides default settings optimized for desktop usage.

PROBLEMS

       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 [1].  See also [2] and [3].

       • Linux  kernels  without  CONFIG_CGROUP_CPUACCT=y (linux-ck, for example) provide incorrect PSI metrics,
         see this thread [4].

HOW TO CONFIGURE

       The program can be configured by editing the config file.  The configuration includes the following  sec‐
       tions:

       • 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

       • GUI notifications:

         • notifications of corrective actions taken

         • low memory warnings

       • Verbosity

       • Misc

       Just  read  the  description  of  the  parameters  and  edit the values.  Restart the daemon to apply the
       changes.

CHECK CONFIG

       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.

LOGGING

       To view the latest entries in the log (for systemd users):

       $ sudo journalctl -eu nohang.service

       or

       $ sudo journalctl -eu nohang-desktop.service

       You can also enable separate_log in the config to logging in /var/log/nohang/nohang.log.

SIGNALS

       Sending SIGTERM, SIGINT, SIGQUIT or SIGHUP signals to the nohang process causes  it  displays  corrective
       action stats and exits.

REPORTING BUGS

       Please ask any questions and report bugs at <https://github.com/hakavlad/nohang/issues>.

AUTHOR

       Written by Alexey Avramov <hakavlad@gmail.com>.

HOMEPAGE

       Homepage is <https://github.com/hakavlad/nohang>.

SEE ALSO

       oom-sort(1), psi-top(1), psi2log(1)

NOTES

       1. https://github.com/openzfs/zfs/issues/10255

       2. https://github.com/rfjakob/earlyoom/pull/191#issuecomment-622314296

       3. https://github.com/hakavlad/nohang/issues/89

       4. https://github.com/hakavlad/nohang/issues/25#issuecomment-521390412

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