1nohang(8)             Linux System Administrator's Manual            nohang(8)
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NAME

6       nohang - A sophisticated low memory handler
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SYNOPSIS

9       nohang [OPTION]...
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DESCRIPTION

12       nohang  is a highly configurable daemon for Linux which is able to cor‐
13       rectly prevent out of memory (OOM) and keep  system  responsiveness  in
14       low memory conditions.
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REQUIREMENTS

17   For basic usage:
18       · Linux (>= 3.14, since MemAvailable appeared in /proc/meminfo)
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20       · Python (>= 3.3)
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22   To respond to PSI metrics (optional):
23       · Linux (>= 4.20) with CONFIG_PSI=y
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25   To show GUI notifications (optional):
26       · notification  server  (most of desktop environments use their own im‐
27         plementations)
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29       · libnotify (Arch Linux, Fedora,  openSUSE)  or  libnotify-bin  (Debian
30         GNU/Linux, Ubuntu)
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32       · sudo if nohang started with UID=0.
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COMMAND-LINE OPTIONS

35   -h, --help
36       show this help message and exit
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38   -v, --version
39       show version of installed package and exit
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41   -m, --memload
42       consume  memory until 40 MiB (MemAvailable + SwapFree) remain free, and
43       terminate the process
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45   -c CONFIG, --config CONFIG
46       path to the config file.  This should only be used with one of the fol‐
47       lowing options: --monitor, --tasks, --check
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49   --check
50       check  and  show  the configuration and exit.  This should only be used
51       with -c/--config CONFIG option
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53   --monitor
54       start monitoring.  This should only be used with -c/--config CONFIG op‐
55       tion
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57   --tasks
58       show  tasks  state and exit.  This should only be used with -c/--config
59       CONFIG option
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FILES

62   /etc/nohang/nohang.conf
63       path to vanilla nohang configuration file
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65   /etc/nohang/nohang-desktop.conf
66       path to configuration file with settings optimized for desktop usage
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68   /usr/share/nohang/nohang.conf
69       path to file with default nohang.conf values
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71   /usr/share/nohang/nohang-desktop.conf
72       path to file with default nohang-desktop.conf values
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74   /var/log/nohang/nohang.log
75       optional log file that stores entries if separate_log=True in the  con‐
76       fig
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78   /etc/logrotate.d/nohang
79       logrotate config file that controls rotation in /var/log/nohang/
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nohang.conf vs nohang-desktop.conf

82       · nohang.conf  provides  vanilla  default settings without PSI checking
83         enabled, without any badness correction and without GUI notifications
84         enabled.
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86       · nohang-desktop.conf  provides  default settings optimized for desktop
87         usage.
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PROBLEMS

90       The next problems can occur with out-of-tree kernels and modules:
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92       · The ZFS ARC cache is memory-reclaimable, like the Linux buffer cache.
93         However, in contrast to the buffer cache, it currently does not count
94         to MemAvailable [1].  See also [2] and [3].
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96       · Linux kernels without CONFIG_CGROUP_CPUACCT=y (linux-ck, for example)
97         provide incorrect PSI metrics, see this thread [4].
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HOW TO CONFIGURE

100       The program can be configured by editing the config file.  The configu‐
101       ration includes the following sections:
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103       · Memory levels to respond to as an OOM threat
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105       · Response on PSI memory metrics
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107       · The frequency of checking the level of available memory (and CPU  us‐
108         age)
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110       · The prevention of killing innocent victims
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112       · Impact on the badness of processes via matching their names, cmdlines
113         and UIDs with regular expressions
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115       · The execution of a specific command or sending any signal instead  of
116         sending the SIGTERM signal
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118       · GUI notifications:
119
120         · notifications of corrective actions taken
121
122         · low memory warnings
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124       · Verbosity
125
126       · Misc
127
128       Just  read  the  description  of  the  parameters  and edit the values.
129       Restart the daemon to apply the changes.
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CHECK CONFIG

132       Check the config for errors:
133
134       $ nohang --check --config /path/to/config
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HOW TO TEST

137       The safest way is to run nohang --memload.  This causes memory consump‐
138       tion,  and the process will exits before OOM occurs.  Another way is to
139       run tail /dev/zero.  This causes fast memory comsumption and causes OOM
140       at the end.  If testing occurs while nohang is running, these processes
141       should be terminated before OOM occurs.
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LOGGING

144       To view the latest entries in the log (for systemd users):
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146       $ sudo journalctl -eu nohang.service
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148       or
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150       $ sudo journalctl -eu nohang-desktop.service
151
152       You  can  also  enable  separate_log  in  the  config  to  logging   in
153       /var/log/nohang/nohang.log.
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SIGNALS

156       Sending  SIGTERM,  SIGINT,  SIGQUIT  or  SIGHUP  signals  to the nohang
157       process causes it displays corrective action stats and exits.
158

REPORTING BUGS

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

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

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

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

173       1. https://github.com/openzfs/zfs/issues/10255
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175       2. https://github.com/rfjakob/earlyoom/pull/191#issuecomment-622314296
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177       3. https://github.com/hakavlad/nohang/issues/89
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179       4. https://github.com/hakavlad/nohang/issues/25#issuecomment-521390412
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