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 correction 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 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

       • 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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