---
name: "nohang"
section: "8"
platform: "linux"
package: "nohang"
version: "0.2.0-3"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/nohang"
---

# nohang(8)

A sophisticated low memory handler

## 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)](/oom-sort/1.md), [psi-top(1)](/psi-top/1.md), [psi2log(1)](/psi2log/1.md)

## 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