nohang

nohang package provides a highly configurable daemon for Linux which is able to correctly prevent out of memory (OOM) and keep system responsiveness in low memory conditions.

The package also includes additional diagnostic tools (oom-sort, psi2log, psi-top).

What is the problem?

OOM conditions may cause freezes, livelocks, drop caches and processes to be killed (via sending SIGKILL) instead of trying to terminate them correctly (via sending SIGTERM or takes other corrective action). Some applications may crash if it's impossible to allocate memory.

Here are the statements of some users:

"How do I prevent Linux from freezing when out of memory? Today I (accidentally) ran some program on my Linux box that quickly used a lot of memory. My system froze, became unresponsive and thus I was unable to kill the offender. How can I prevent this in the future? Can't it at least keep a responsive core or something running?"

— serverfault

"With or without swap it still freezes before the OOM killer gets run automatically. This is really a kernel bug that should be fixed (i.e. run OOM killer earlier, before dropping all disk cache). Unfortunately kernel developers and a lot of other folk fail to see the problem. Common suggestions such as disable/enable swap, buy more RAM, run less processes, set limits etc. do not address the underlying problem that the kernel's low memory handling sucks camel's balls."

— serverfault

"The traditional Linux OOM killer works fine in some cases, but in others it kicks in too late, resulting in the system entering a livelock for an indeterminate period."

— engineering.fb.com

Also look at these discussions:

Why are low memory conditions handled so badly? [r/linux]
Memory management "more effective" on Windows than Linux? (in preventing total system lockup) [r/linux]
Let's talk about the elephant in the room - the Linux kernel's inability to gracefully handle low memory pressure [original LKML post | r/linux | Hacker News | slashdot | phoronix | opennet.ru | linux.org.ru]

Solution

Use one of the userspace OOM killers:

earlyoom: This is a simple, stable and tiny OOM prevention daemon written in C (the best choice for emedded and old servers). It has a minimum dependencies and can work with oldest kernels. It is enabled by default on Fedora 32 Workstation (and F33 KDE).
oomd: This is a userspace OOM killer for linux systems written in C++ and developed by Facebook. This is the best choice for use in large data centers. It needs Linux 4.20+.
systemd-oomd: Provided by systemd as systemd-oomd.service that uses cgroups-v2 and pressure stall information (PSI) to monitor and take action on processes before an OOM occurs in kernel space. It's used by default on desktop versions of Fedora 34.
low-memory-monitor: There's a project announcement.
psi-monitor: It's used by default on Endless OS.
nohang: nohang is earlyoom on steroids and has many useful features, see below. Maybe this is a good choice for modern desktops and servers if you need fine-tuning. It's used by default on Garuda Linux.

Use these tools to improve responsiveness during heavy swapping:

le9-patch: [PATCH] mm: Protect clean file pages under memory pressure to prevent thrashing, avoid high latency and prevent livelock in near-OOM conditions. It's kernel-side solution that can fix the OOM killer behavior.
prelockd: Lock executables and shared libraries in memory to improve system responsiveness under low-memory conditions.
memavaild: Keep amount of available memory by evicting memory of selected cgroups into swap space.
uresourced: This daemon will give resource allocations to active graphical users. It's enabled by default on Fedora 33 Workstation.

Of course, you can also download more RAM, tune virtual memory, use zram/zswap and use limits for cgroups.

Features

Sending the SIGTERM signal is default corrective action. If the victim does not respond to SIGTERM, with a further drop in the level of memory it gets SIGKILL;
Customizing victim selection: impact on the badness of processes via matching their names, cgroups, exe realpathes, environs, cmdlines and euids with specified regular expressions;
Customizing corrective actions: if the name or control group of the victim matches a certain regex pattern, you can run any command instead of sending the SIGTERM signal (the default corrective action) to the victim. For example:
- systemctl restart foo;
- kill -INT $PID (you can override the signal sent to the victim, $PID will be replaced by the victim's PID).
GUI notifications:
- Notification of corrective actions taken and displaying the name and PID of the victim;
- Low memory warnings.
zram support (mem_used_total as a trigger);
PSI (pressure stall information) support;
Optional checking kernel messages for OOM events;
Easy setup with configuration files (nohang.conf, nohang-desktop.conf).

Demo

nohang prevents Out Of Memory with GUI notifications:

https://youtu.be/ChTNu9m7uMU – just old demo without swap space.
https://youtu.be/UCwZS5uNLu0 – running multiple fast memory hogs at the same time without swap space.
https://youtu.be/PLVWgNrVNlc – opening multiple chromium tabs with 2.3 GiB memory and 1.8 GiB swap space on zram.

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.

Memory and CPU usage

VmRSS is about 10–14 MiB instead of the settings, about 10–11 MiB by default (with Python <= 3.8), about 16–17 MiB with Python 3.9.
CPU usage depends on the level of available memory and monitoring intensity.

Warnings

the daemon runs with super-user privileges and has full access to all private memory of all processes and sensitive user data;
the daemon does not forbid you to shoot yourself in the foot: with some settings, unwanted killings of processes can occur;
the daemon is not a panacea: there are no universal settings that reliably protect against all types of threats.

Known problems

The documentation is terrible.
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 openzfs/zfs#10255). See also rfjakob/earlyoom#191 and hakavlad#89.
Linux kernels without CONFIG_CGROUP_CPUACCT=y (linux-ck, for example) provide incorrect PSI metrics, see issue.

nohang vs nohang-desktop

nohang comes with two configs: nohang.conf and nohang-desktop.conf. nohang comes with two systemd service unit files: nohang.service and nohang-desktop.service. Choose one.

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.

How to install

To install on Fedora:

$ sudo dnf install nohang-desktop
$ sudo systemctl enable --now nohang-desktop.service

To install on RHEL 7 and RHEL 8:

nohang is avaliable in EPEL repos.

$ sudo yum install nohang
$ sudo systemctl enable nohang.service
$ sudo systemctl start nohang.service

To enable PSI on RHEL 8 pass psi=1 to kernel boot cmdline.

For Arch Linux there's an AUR package

Use your favorite AUR helper. For example,

$ yay -S nohang-git
$ sudo systemctl enable --now nohang-desktop.service

To install on Ubuntu 20.04/20.10

To install from PPA:

$ sudo add-apt-repository ppa:oibaf/test
$ sudo apt update
$ sudo apt install nohang
$ sudo systemctl enable --now nohang-desktop.service

To install on Debian and Ubuntu-based systems:

Outdated and buggy nohang v0.1 release was packaged for Debian 11 and Ubuntu 20.10.

It's easy to build a deb package with the latest git snapshot. Install build dependencies:

$ sudo apt install make fakeroot

Clone the latest git snapshot and run the build script to build the package:

$ git clone https://github.com/hakavlad/nohang.git && cd nohang
$ deb/build.sh

Install the package:

$ sudo apt install --reinstall ./deb/package.deb

Start and enable nohang.service or nohang-desktop.service after installing the package:

$ sudo systemctl enable --now nohang-desktop.service

To install on Gentoo and derivatives (e.g. Funtoo):

Add the eph kit overlay, for example using layman or as a local repository. Then update your repos:

$ sudo layman -S # if added via layman
$ sudo emerge --sync # local repo on Gentoo
$ sudo ego sync # local repo on Funtoo

Install:

$ sudo emerge -a nohang

Start the service:

$ sudo rc-service nohang-desktop start

Optionally add to startup:

$ sudo rc-update add nohang-desktop default

To install the latest version on any distro:

$ git clone https://github.com/hakavlad/nohang.git && cd nohang
$ sudo make install

Config files will be located in /usr/local/etc/nohang/. To enable and start unit without GUI notifications:

$ sudo systemctl enable --now nohang.service

To enable and start unit with GUI notifications:

$ sudo systemctl enable --now nohang-desktop.service

On systems with OpenRC:

$ sudo make install-openrc

To uninstall:

$ sudo make uninstall

Command line options

./nohang -h
usage: nohang [-h|--help] [-v|--version] [-m|--memload]
              [-c|--config CONFIG] [--check] [--monitor] [--tasks]

optional arguments:
  -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

How to configure

The program can be configured by editing the config file. The configuration includes the following sections:

Checking kernel messages for OOM events;
Common zram settings;
Common PSI settings;
Poll rate;
Warnings and notifications;
Soft threshold;
Hard threshold;
Customize victim selection;
Customize soft corrective actions;
Misc settings;
Verbosity, debug, logging.

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

How to test nohang

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.

Tasks state

Run sudo nohang -c/--config CONFIG --tasks to see the table of prosesses with their badness values, oom_scores, names, UIDs etc.

Output example

Config: /etc/nohang/nohang.conf
###################################################################################################################
#    PID     PPID  badness  oom_score  oom_score_adj        eUID  S  VmSize  VmRSS  VmSwap  Name             CGroup
#-------  -------  -------  ---------  -------------  ----------  -  ------  -----  ------  ---------------  --------
#    336        1        1          1              0           0  S      85     25       0  systemd-journal  /system.slice/systemd-journald.service
#    383        1        0          0          -1000           0  S      46      5       0  systemd-udevd    /system.slice/systemd-udevd.service
#    526     2238        7          7              0        1000  S     840     96       0  kate             /user.slice/user-1000.slice/session-7.scope
#    650        1        3          3              0        1000  S     760     50       0  kate             /user.slice/user-1000.slice/session-7.scope
#    731        1        0          0              0         100  S     126      4       0  systemd-timesyn  /system.slice/systemd-timesyncd.service
#    756        1        0          0              0         105  S     181      3       0  rtkit-daemon     /system.slice/rtkit-daemon.service
#    759        1        0          0              0           0  S     277      7       0  accounts-daemon  /system.slice/accounts-daemon.service
#    761        1        0          0              0           0  S     244      3       0  rsyslogd         /system.slice/rsyslog.service
#    764        1        0          0           -900         108  S      45      5       0  dbus-daemon      /system.slice/dbus.service
#    805        1        0          0              0           0  S      46      5       0  systemd-logind   /system.slice/systemd-logind.service
#    806        1        0          0              0           0  S      35      3       0  irqbalance       /system.slice/irqbalance.service
#    813        1        0          0              0           0  S      29      3       0  cron             /system.slice/cron.service
#    814        1       11         11              0           0  S     176    160       0  memlockd         /system.slice/memlockd.service
#    815        1        0          0            -10           0  S      32      9       0  python3          /fork.slice/fork-bomb.slice/fork-bomb-killer.slice/fork-bomb-killer.service
#    823        1        0          0              0           0  S      25      4       0  smartd           /system.slice/smartd.service
#    826        1        0          0              0         113  S      46      3       0  avahi-daemon     /system.slice/avahi-daemon.service
#    850      826        0          0              0         113  S      46      0       0  avahi-daemon     /system.slice/avahi-daemon.service
#    868        1        0          0              0           0  S     281      8       0  polkitd          /system.slice/polkit.service
#    903        1        1          1              0           0  S    4094     16       0  stunnel4         /system.slice/stunnel4.service
#    940        1        0          0           -600           0  S      39     10       0  python3          /nohang.slice/nohang.service
#   1014        1        0          0              0          13  S      22      2       0  obfs-local       /system.slice/obfs-local.service
#   1015        1        0          0              0        1000  S      36      4       0  ss-local         /system.slice/ss-local.service
#   1023        1        0          0              0         116  S      33      2       0  dnscrypt-proxy   /system.slice/dnscrypt-proxy.service
#   1029        1        1          1              0         119  S    4236     16       0  privoxy          /system.slice/privoxy.service
#   1035        1        0          0              0           0  S     355      6       0  lightdm          /system.slice/lightdm.service
#   1066        1        0          0              0           0  S      45      7       0  wpa_supplicant   /system.slice/wpa_supplicant.service
#   1178        1        0          0              0           0  S      14      2       0  agetty           /system.slice/system-getty.slice/getty@tty1.service
#   1294        1        0          0          -1000           0  S       4      1       0  watchdog         /system.slice/watchdog.service
#   1632        1        1          1              0        1000  S    1391     22       0  pulseaudio       /user.slice/user-1000.slice/session-2.scope
#   1689     1632        0          0              0        1000  S     125      5       0  gconf-helper     /user.slice/user-1000.slice/session-2.scope
#   1711        1        0          0              0           0  S     367      8       0  udisksd          /system.slice/udisks2.service
#   1819        1        0          0              0           0  S     304      8       0  upowerd          /system.slice/upower.service
#   1879        1        0          0              0        1000  S      64      7       0  systemd          /user.slice/user-1000.slice/user@1000.service/init.scope
#   1880     1879        0          0              0        1000  S     229      2       0  (sd-pam)         /user.slice/user-1000.slice/user@1000.service/init.scope
#   1888        1        0          0              0           0  S      14      2       0  agetty           /system.slice/system-getty.slice/getty@tty2.service
#   1889        1        0          0              0           0  S      14      2       0  agetty           /system.slice/system-getty.slice/getty@tty3.service
#   1890        1        0          0              0           0  S      14      2       0  agetty           /system.slice/system-getty.slice/getty@tty4.service
#   1891        1        0          0              0           0  S      14      2       0  agetty           /system.slice/system-getty.slice/getty@tty5.service
#   1892        1        0          0              0           0  S      14      2       0  agetty           /system.slice/system-getty.slice/getty@tty6.service
#   1893     1035       14         14              0           0  R     623    208       0  Xorg             /system.slice/lightdm.service
#   1904        1        0          0              0         111  S      64      7       0  systemd          /user.slice/user-111.slice/user@111.service/init.scope
#   1905     1904        0          0              0         111  S     229      2       0  (sd-pam)         /user.slice/user-111.slice/user@111.service/init.scope
#   1916     1904        0          0              0         111  S      44      3       0  dbus-daemon      /user.slice/user-111.slice/user@111.service/dbus.service
#   1920        1        0          0              0         111  S     215      5       0  at-spi2-registr  /user.slice/user-111.slice/session-c2.scope
#   1922     1904        0          0              0         111  S     278      6       0  gvfsd            /user.slice/user-111.slice/user@111.service/gvfs-daemon.service
#   1935     1035        0          0              0           0  S     238      6       0  lightdm          /user.slice/user-1000.slice/session-7.scope
#   1942        1        0          0              0        1000  S     210      9       0  gnome-keyring-d  /user.slice/user-1000.slice/session-7.scope
#   1944     1935        1          1              0        1000  S     411     21       0  mate-session     /user.slice/user-1000.slice/session-7.scope
#   1952     1879        0          0              0        1000  S      45      5       0  dbus-daemon      /user.slice/user-1000.slice/user@1000.service/dbus.service
#   1981     1944        0          0              0        1000  S      11      0       0  ssh-agent        /user.slice/user-1000.slice/session-7.scope
#   1984     1879        0          0              0        1000  S     278      6       0  gvfsd            /user.slice/user-1000.slice/user@1000.service/gvfs-daemon.service
#   1990     1879        0          0              0        1000  S     341      5       0  at-spi-bus-laun  /user.slice/user-1000.slice/user@1000.service/at-spi-dbus-bus.service
#   1995     1990        0          0              0        1000  S      44      4       0  dbus-daemon      /user.slice/user-1000.slice/user@1000.service/at-spi-dbus-bus.service
#   1997     1879        0          0              0        1000  S     215      5       0  at-spi2-registr  /user.slice/user-1000.slice/user@1000.service/at-spi-dbus-bus.service
#   2000     1879        0          0              0        1000  S     184      5       0  dconf-service    /user.slice/user-1000.slice/user@1000.service/dbus.service
#   2009     1944        2          2              0        1000  S    1308     35       0  mate-settings-d  /user.slice/user-1000.slice/session-7.scope
#   2013     1944        2          2              0        1000  S     436     32       0  marco            /user.slice/user-1000.slice/session-7.scope
#   2024     1944        4          4              0        1000  S    1258     55       0  caja             /user.slice/user-1000.slice/session-7.scope
#   2032        1        1          1              0        1000  S     333     18       0  msd-locate-poin  /user.slice/user-1000.slice/session-7.scope
#   2033     1879        0          0              0        1000  S     348     11       0  gvfs-udisks2-vo  /user.slice/user-1000.slice/user@1000.service/gvfs-udisks2-volume-monitor.service
#   2036     1944        1          1              0        1000  S     331     17       0  polkit-mate-aut  /user.slice/user-1000.slice/session-7.scope
#   2038     1944        5          5              0        1000  S     682     78       0  mate-panel       /user.slice/user-1000.slice/session-7.scope
#   2041     1944        2          2              0        1000  S     514     31       0  nm-applet        /user.slice/user-1000.slice/session-7.scope
#   2046     1944        1          1              0        1000  S     495     25       0  mate-power-mana  /user.slice/user-1000.slice/session-7.scope
#   2047     1944        2          2              0        1000  S     692     32       0  mate-volume-con  /user.slice/user-1000.slice/session-7.scope
#   2049     1944        3          3              0        1000  S     548     44       0  mate-screensave  /user.slice/user-1000.slice/session-7.scope
#   2059     1879        0          0              0        1000  S     263      5       0  gvfs-goa-volume  /user.slice/user-1000.slice/user@1000.service/gvfs-goa-volume-monitor.service
#   2076     1879        0          0              0        1000  S     352      7       0  gvfsd-trash      /user.slice/user-1000.slice/user@1000.service/gvfs-daemon.service
#   2077     1879        0          0              0        1000  S     362      7       0  gvfs-afc-volume  /user.slice/user-1000.slice/user@1000.service/gvfs-afc-volume-monitor.service
#   2087     1879        0          0              0        1000  S     263      5       0  gvfs-mtp-volume  /user.slice/user-1000.slice/user@1000.service/gvfs-mtp-volume-monitor.service
#   2093     1879        0          0              0        1000  S     275      6       0  gvfs-gphoto2-vo  /user.slice/user-1000.slice/user@1000.service/gvfs-gphoto2-volume-monitor.service
#   2106     1879        3          3              0        1000  S     544     42       0  wnck-applet      /user.slice/user-1000.slice/user@1000.service/dbus.service
#   2108     1879        1          1              0        1000  S     396     21       0  notification-ar  /user.slice/user-1000.slice/user@1000.service/dbus.service
#   2112     1879        1          1              0        1000  S     499     25       0  mate-sensors-ap  /user.slice/user-1000.slice/user@1000.service/dbus.service
#   2113     1879        1          1              0        1000  S     390     21       0  mate-brightness  /user.slice/user-1000.slice/user@1000.service/dbus.service
#   2114     1879        1          1              0        1000  S     534     22       0  mate-multiload-  /user.slice/user-1000.slice/user@1000.service/dbus.service
#   2118     1879        2          2              0        1000  S     547     29       0  clock-applet     /user.slice/user-1000.slice/user@1000.service/dbus.service
#   2152     1879        1          1              0        1000  S     218     22       0  gvfsd-metadata   /user.slice/user-1000.slice/user@1000.service/gvfs-metadata.service
#   2206        1        3          3              0         110  S     106     48       0  tor              /system.slice/system-tor.slice/tor@default.service
#   2229        1        3          3              0        1000  S     999     42       0  kactivitymanage  /user.slice/user-1000.slice/session-7.scope
#   2238        1        0          0              0        1000  S     150      9       0  kdeinit5         /user.slice/user-1000.slice/session-7.scope
#   2239     2238        3          3              0        1000  S     648     41       0  klauncher        /user.slice/user-1000.slice/session-7.scope
#   3959        1        1          1              0           0  S     615     18       0  NetworkManager   /system.slice/NetworkManager.service
#   3977     3959        0          0              0           0  S      20      4       0  dhclient         /system.slice/NetworkManager.service
#   5626     1879        0          0              0        1000  S     355      7       0  gvfsd-network    /user.slice/user-1000.slice/user@1000.service/gvfs-daemon.service
#   5637     1879        1          1              0        1000  S     623     14       0  gvfsd-smb-brows  /user.slice/user-1000.slice/user@1000.service/gvfs-daemon.service
#   6296     1879        0          0              0        1000  S     435      7       0  gvfsd-dnssd      /user.slice/user-1000.slice/user@1000.service/gvfs-daemon.service
#  11129     1879        3          3              0        1000  S     597     42       0  kded5            /user.slice/user-1000.slice/user@1000.service/dbus.service
#  11136     1879        2          2              0        1000  S     639     39       0  kuiserver5       /user.slice/user-1000.slice/user@1000.service/dbus.service
#  11703     1879        3          3              0        1000  S     500     45       0  mate-system-mon  /user.slice/user-1000.slice/user@1000.service/dbus.service
#  16798     1879        0          0              0        1000  S     346     10       0  gvfsd-http       /user.slice/user-1000.slice/user@1000.service/gvfs-daemon.service
#  18133        1        3          3              0        1000  S     760     49       0  kate             /user.slice/user-1000.slice/session-7.scope
#  18144     2038        1          1              0        1000  S     301     23       0  lxterminal       /user.slice/user-1000.slice/session-7.scope
#  18147    18144        0          0              0        1000  S      14      2       0  gnome-pty-helpe  /user.slice/user-1000.slice/session-7.scope
#  18148    18144        1          1              0        1000  S      42     26       0  bash             /user.slice/user-1000.slice/session-7.scope
#  18242     2238        1          1              0        1000  S     194     14       0  file.so          /user.slice/user-1000.slice/session-7.scope
#  18246    18148        0          0              0           0  S      54      4       0  sudo             /user.slice/user-1000.slice/session-7.scope
#  19003        1        0          0              0           0  S     310     12       0  packagekitd      /system.slice/packagekit.service
#  26993     2038       91         91              0        1000  S    3935   1256       0  firefox-esr      /user.slice/user-1000.slice/session-7.scope
#  27275    26993      121        121              0        1000  S    3957   1684       0  Web Content      /user.slice/user-1000.slice/session-7.scope
#  30374        1        1          1              0        1000  S     167     14       0  VBoxXPCOMIPCD    /user.slice/user-1000.slice/session-7.scope
#  30380        1        2          2              0        1000  S     958     27       0  VBoxSVC          /user.slice/user-1000.slice/session-7.scope
#  30549    30380       86         86              0        1000  S    5332   1192       0  VirtualBox       /user.slice/user-1000.slice/session-7.scope
#  30875        1        1          1              0        1000  S     345     26       0  leafpad          /user.slice/user-1000.slice/session-7.scope
#  32689        1        7          7              0        1000  S     896     99       0  dolphin          /user.slice/user-1000.slice/session-7.scope
###################################################################################################################
Process with highest badness (found in 55 ms):
  PID: 27275, Name: Web Content, badness: 121

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.

oom-sort

oom-sort is an additional diagnostic tool that will be installed with nohang package. It sorts the processes in descending order of their oom_score and also displays oom_score_adj, Uid, Pid, Name, VmRSS, VmSwap and optionally cmdline. Run oom-sort --help for more info. Man page: oom-sort.manpage.md.

Usage:

$ oom-sort

Output example

oom_score oom_score_adj  UID   PID Name            VmRSS   VmSwap   cmdline
--------- ------------- ---- ----- --------------- ------- -------- -------
       23             0    0   964 Xorg               58 M     22 M /usr/libexec/Xorg -background none :0 vt01 -nolisten tcp -novtswitch -auth /var/run/lxdm/lxdm-:0.auth
       13             0 1000  1365 pcmanfm            38 M     10 M pcmanfm --desktop --profile LXDE
       10             0 1000  1408 dnfdragora-upda     9 M     27 M /usr/bin/python3 /bin/dnfdragora-updater
        5             0    0   822 firewalld           0 M     19 M /usr/bin/python3 /usr/sbin/firewalld --nofork --nopid
        5             0 1000  1364 lxpanel            18 M      2 M lxpanel --profile LXDE
        5             0 1000  1685 nm-applet           6 M     12 M nm-applet
        5             0 1000  1862 lxterminal         16 M      2 M lxterminal
        4             0  996   890 polkitd             8 M      6 M /usr/lib/polkit-1/polkitd --no-debug
        4             0 1000  1703 pnmixer             6 M     11 M pnmixer
        3             0    0   649 systemd-journal    10 M      1 M /usr/lib/systemd/systemd-journald
        3             0 1000  1360 openbox             9 M      2 M openbox --config-file /home/user/.config/openbox/lxde-rc.xml
        3             0 1000  1363 notification-da     3 M     10 M /usr/libexec/notification-daemon
        2             0 1000  1744 clipit              5 M      3 M clipit
        2             0 1000  2619 python3             9 M      0 M python3 /bin/oom-sort
        1             0    0   809 rsyslogd            3 M      3 M /usr/sbin/rsyslogd -n
        1             0    0   825 udisksd             2 M      2 M /usr/libexec/udisks2/udisksd
        1             0    0   873 sssd_nss            4 M      1 M /usr/libexec/sssd/sssd_nss --uid 0 --gid 0 --logger=files
        1             0    0   876 systemd-logind      2 M      2 M /usr/lib/systemd/systemd-logind
        1             0    0   907 abrt-dump-journ     2 M      1 M /usr/bin/abrt-dump-journal-oops -fxtD
        1             0    0   920 NetworkManager      3 M      2 M /usr/sbin/NetworkManager --no-daemon
        1             0 1000  1115 systemd             4 M      1 M /usr/lib/systemd/systemd --user
        1             0 1000  1118 (sd-pam)            0 M      5 M (sd-pam)
        1             0 1000  1366 xscreensaver        5 M      0 M xscreensaver -no-splash
        1             0 1000  1851 gvfsd-trash         3 M      1 M /usr/libexec/gvfsd-trash --spawner :1.6 /org/gtk/gvfs/exec_spaw/0
        1             0 1000  1969 gvfsd-metadata      6 M      0 M /usr/libexec/gvfsd-metadata
        1             0 1000  2262 bash                5 M      0 M bash
        0         -1000    0   675 systemd-udevd       0 M      4 M /usr/lib/systemd/systemd-udevd
        0         -1000    0   787 auditd              0 M      1 M /sbin/auditd
        0             0    0   807 ModemManager        0 M      1 M /usr/sbin/ModemManager
        0             0    0   808 smartd              0 M      1 M /usr/sbin/smartd -n -q never
        0             0    0   810 alsactl             0 M      0 M /usr/sbin/alsactl -s -n 19 -c -E ALSA_CONFIG_PATH=/etc/alsa/alsactl.conf --initfile=/lib/alsa/init/00main rdaemon
        0             0    0   811 mcelog              0 M      0 M /usr/sbin/mcelog --ignorenodev --daemon --foreground
        0             0  172   813 rtkit-daemon        0 M      0 M /usr/libexec/rtkit-daemon
        0             0    0   814 VBoxService         0 M      1 M /usr/sbin/VBoxService -f
        0             0    0   817 rngd                0 M      1 M /sbin/rngd -f
        0          -900   81   818 dbus-daemon         3 M      0 M /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
        0             0    0   823 irqbalance          0 M      0 M /usr/sbin/irqbalance --foreground
        0             0   70   824 avahi-daemon        0 M      0 M avahi-daemon: running [linux.local]
        0             0    0   826 sssd                0 M      2 M /usr/sbin/sssd -i --logger=files
        0             0  995   838 chronyd             1 M      0 M /usr/sbin/chronyd
        0             0    0   849 gssproxy            0 M      1 M /usr/sbin/gssproxy -D
        0             0    0   866 abrtd               0 M      2 M /usr/sbin/abrtd -d -s
        0             0   70   870 avahi-daemon        0 M      0 M avahi-daemon: chroot helper
        0             0    0   871 sssd_be             0 M      2 M /usr/libexec/sssd/sssd_be --domain implicit_files --uid 0 --gid 0 --logger=files
        0             0    0   875 accounts-daemon     0 M      1 M /usr/libexec/accounts-daemon
        0             0    0   906 abrt-dump-journ     1 M      2 M /usr/bin/abrt-dump-journal-core -D -T -f -e
        0             0    0   908 abrt-dump-journ     1 M      2 M /usr/bin/abrt-dump-journal-xorg -fxtD
        0             0    0   950 crond               2 M      1 M /usr/sbin/crond -n
        0             0    0   951 atd                 0 M      0 M /usr/sbin/atd -f
        0             0    0   953 lxdm-binary         0 M      0 M /usr/sbin/lxdm-binary
        0             0    0  1060 dhclient            0 M      2 M /sbin/dhclient -d -q -sf /usr/libexec/nm-dhcp-helper -pf /var/run/dhclient-enp0s3.pid -lf /var/lib/NetworkManager/dhclient-939eab05-4796-3792-af24-9f76cf53ca7f-enp0s3.lease -cf /var/lib/NetworkManager/dhclient-enp0s3.conf enp0s3
        0             0    0  1105 lxdm-session        0 M      1 M /usr/libexec/lxdm-session
        0             0 1000  1123 pulseaudio          0 M      3 M /usr/bin/pulseaudio --daemonize=no
        0             0 1000  1124 lxsession           1 M      2 M /usr/bin/lxsession -s LXDE -e LXDE
        0             0 1000  1134 dbus-daemon         2 M      0 M /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
        0             0 1000  1215 imsettings-daem     0 M      1 M /usr/libexec/imsettings-daemon
        0             0 1000  1218 gvfsd               3 M      1 M /usr/libexec/gvfsd
        0             0 1000  1223 gvfsd-fuse          0 M      1 M /usr/libexec/gvfsd-fuse /run/user/1000/gvfs -f -o big_writes
        0             0 1000  1309 VBoxClient          0 M      0 M /usr/bin/VBoxClient --display
        0             0 1000  1310 VBoxClient          0 M      0 M /usr/bin/VBoxClient --clipboard
        0             0 1000  1311 VBoxClient          0 M      0 M /usr/bin/VBoxClient --draganddrop
        0             0 1000  1312 VBoxClient          0 M      0 M /usr/bin/VBoxClient --display
        0             0 1000  1313 VBoxClient          1 M      0 M /usr/bin/VBoxClient --clipboard
        0             0 1000  1316 VBoxClient          0 M      0 M /usr/bin/VBoxClient --seamless
        0             0 1000  1318 VBoxClient          0 M      0 M /usr/bin/VBoxClient --seamless
        0             0 1000  1320 VBoxClient          0 M      0 M /usr/bin/VBoxClient --draganddrop
        0             0 1000  1334 ssh-agent           0 M      0 M /usr/bin/ssh-agent /bin/sh -c exec -l bash -c "/usr/bin/startlxde"
        0             0 1000  1362 lxpolkit            0 M      1 M lxpolkit
        0             0 1000  1370 lxclipboard         0 M      1 M lxclipboard
        0             0 1000  1373 ssh-agent           0 M      1 M /usr/bin/ssh-agent -s
        0             0 1000  1485 agent               0 M      1 M /usr/libexec/geoclue-2.0/demos/agent
        0             0 1000  1751 menu-cached         0 M      1 M /usr/libexec/menu-cache/menu-cached /run/user/1000/menu-cached-:0
        0             0 1000  1780 at-spi-bus-laun     0 M      1 M /usr/libexec/at-spi-bus-launcher
        0             0 1000  1786 dbus-daemon         1 M      0 M /usr/bin/dbus-daemon --config-file=/usr/share/defaults/at-spi2/accessibility.conf --nofork --print-address 3
        0             0 1000  1792 at-spi2-registr     1 M      1 M /usr/libexec/at-spi2-registryd --use-gnome-session
        0             0 1000  1840 gvfs-udisks2-vo     0 M      2 M /usr/libexec/gvfs-udisks2-volume-monitor
        0             0 1000  1863 gnome-pty-helpe     1 M      0 M gnome-pty-helper
        0             0 1000  1864 bash                0 M      1 M bash
        0             0    0  1899 sudo                0 M      1 M sudo -i
        0             0    0  1901 bash                0 M      1 M -bash
        0             0    0  1953 oomd_bin            0 M      0 M oomd_bin -f /sys/fs/cgroup/unified
        0          -600    0  2562 python3            10 M      0 M python3 /usr/sbin/nohang --config /etc/nohang/nohang.conf

Kthreads, zombies and Pid 1 will not be displayed.

psi-top

psi-top is script that prints the PSI metrics values for every cgroup. It requires Linux >= 4.20 with CONFIG_PSI=y. Man page: psi-top.manpage.md.

Output example

$ psi-top
cgroup2 mountpoint: /sys/fs/cgroup
      avg10  avg60 avg300         avg10  avg60 avg300  cgroup2
      -----  ----- ------         -----  ----- ------  ---------
some   0.00   0.21   1.56 | full   0.00   0.16   1.14  [SYSTEM_WIDE]
some   0.00   0.21   1.56 | full   0.00   0.16   1.14
some   0.00   0.15   1.11 | full   0.00   0.12   0.89  /user.slice
some  45.92  28.77  20.19 | full  45.05  28.17  19.56  /user.slice/user-1000.slice
some   1.44   4.67   9.24 | full   1.44   4.65   9.20  /user.slice/user-1000.slice/user@1000.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /user.slice/user-1000.slice/user@1000.service/pulseaudio.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /user.slice/user-1000.slice/user@1000.service/gvfs-daemon.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /user.slice/user-1000.slice/user@1000.service/dbus.socket
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /user.slice/user-1000.slice/user@1000.service/gvfs-udisks2-volume-monitor.service
some   0.25   1.97   4.05 | full   0.25   1.96   4.03  /user.slice/user-1000.slice/user@1000.service/xfce4-notifyd.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /user.slice/user-1000.slice/user@1000.service/init.scope
some   0.00   0.66   1.99 | full   0.00   0.66   1.97  /user.slice/user-1000.slice/user@1000.service/gpg-agent.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /user.slice/user-1000.slice/user@1000.service/gvfs-gphoto2-volume-monitor.service
some   0.93   0.75   0.20 | full   0.93   0.75   0.20  /user.slice/user-1000.slice/user@1000.service/at-spi-dbus-bus.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /user.slice/user-1000.slice/user@1000.service/gvfs-metadata.service
some   0.00   2.44   6.78 | full   0.00   2.43   6.74  /user.slice/user-1000.slice/user@1000.service/dbus.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /user.slice/user-1000.slice/user@1000.service/gvfs-mtp-volume-monitor.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /user.slice/user-1000.slice/user@1000.service/gvfs-afc-volume-monitor.service
some  44.99  28.30  19.41 | full  44.10  27.70  18.79  /user.slice/user-1000.slice/session-2.scope
some   0.00   0.31   0.53 | full   0.00   0.31   0.53  /init.scope
some   7.25  11.40  13.34 | full   7.23  11.32  13.24  /system.slice
some   0.00   0.01   0.02 | full   0.00   0.01   0.02  /system.slice/systemd-udevd.service
some   0.00   0.58   1.55 | full   0.00   0.58   1.55  /system.slice/cronie.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /system.slice/sys-kernel-config.mount
some   0.00   0.22   0.35 | full   0.00   0.22   0.35  /system.slice/polkit.service
some   0.00   0.06   0.20 | full   0.00   0.06   0.20  /system.slice/rtkit-daemon.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /system.slice/sys-kernel-debug.mount
some   0.00   0.14   0.62 | full   0.00   0.14   0.62  /system.slice/accounts-daemon.service
some   7.86  11.48  12.56 | full   7.84  11.42  12.51  /system.slice/lightdm.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /system.slice/ModemManager.service
some   0.00   1.82   5.47 | full   0.00   1.81   5.43  /system.slice/systemd-journald.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /system.slice/dev-mqueue.mount
some   0.00   1.64   4.07 | full   0.00   1.64   4.07  /system.slice/NetworkManager.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /system.slice/tmp.mount
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /system.slice/lvm2-lvmetad.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /system.slice/dev-disk-by\x2duuid-5d7355c0\x2dc131\x2d40c5\x2d8541\x2d1e04ad7c8b8d.swap
some   0.00   0.09   0.11 | full   0.00   0.09   0.11  /system.slice/upower.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /system.slice/udisks2.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /system.slice/dev-hugepages.mount
some   0.00   0.27   0.49 | full   0.00   0.27   0.48  /system.slice/dbus.service
some   0.00   0.00   0.00 | full   0.00   0.00   0.00  /system.slice/system-getty.slice
some   0.00   0.12   0.20 | full   0.00   0.12   0.20  /system.slice/avahi-daemon.service
some   0.00   0.18   0.30 | full   0.00   0.18   0.30  /system.slice/systemd-logind.service

psi2log

psi2log is a CLI tool that can check and log PSI metrics from specified target. It requires Linux >= 4.20 with CONFIG_PSI=y. Man page: psi2log.manpage.md.

Output example

$ psi2log
Starting psi2log
target: SYSTEM_WIDE
period: 2
------------------------------------------------------------------------------------------------------------------
 some cpu pressure   || some memory pressure | full memory pressure ||  some io pressure    |  full io pressure
---------------------||----------------------|----------------------||----------------------|---------------------
 avg10  avg60 avg300 ||  avg10  avg60 avg300 |  avg10  avg60 avg300 ||  avg10  avg60 avg300 |  avg10  avg60 avg300
------ ------ ------ || ------ ------ ------ | ------ ------ ------ || ------ ------ ------ | ------ ------ ------
  0.13   0.26   0.08 ||   3.36  10.31   3.47 |   2.68   7.69   2.56 ||  20.24  26.90   8.60 |  18.80  23.16   7.33
  0.11   0.25   0.08 ||   2.75   9.97   3.45 |   2.20   7.44   2.54 ||  18.38  26.34   8.61 |  17.21  22.73   7.35
  0.09   0.25   0.07 ||   2.25   9.65   3.43 |   1.80   7.20   2.52 ||  15.05  25.48   8.55 |  14.09  21.99   7.30
  0.07   0.24   0.07 ||   1.84   9.33   3.40 |   1.47   6.96   2.51 ||  13.05  24.78   8.52 |  12.26  21.40   7.28
^C
Peak values:  avg10  avg60 avg300
-----------  ------ ------ ------
some cpu       0.13   0.26   0.08
-----------  ------ ------ ------
some memory    3.36  10.31   3.47
full memory    2.68   7.69   2.56
-----------  ------ ------ ------
some io       20.24  26.90   8.61
full io       18.80  23.16   7.35
$ psi2log -t /user.slice -l pm.log
Starting psi2log
target: /user.slice
period: 2
log file: pm.log
cgroup2 mountpoint: /sys/fs/cgroup
------------------------------------------------------------------------------------------------------------------
 some cpu pressure   || some memory pressure | full memory pressure ||  some io pressure    |  full io pressure
---------------------||----------------------|----------------------||----------------------|---------------------
 avg10  avg60 avg300 ||  avg10  avg60 avg300 |  avg10  avg60 avg300 ||  avg10  avg60 avg300 |  avg10  avg60 avg300
------ ------ ------ || ------ ------ ------ | ------ ------ ------ || ------ ------ ------ | ------ ------ ------
 28.32  11.97   3.03 ||   0.00   1.05   1.65 |   0.00   0.85   1.33 ||   0.55   7.79   7.21 |   0.54   7.52   6.80
 29.53  12.72   3.25 ||   0.00   1.01   1.64 |   0.00   0.82   1.32 ||   0.81   7.60   7.17 |   0.44   7.27   6.76
 29.80  13.32   3.44 ||   0.00   0.98   1.63 |   0.00   0.79   1.31 ||   0.66   7.35   7.12 |   0.36   7.03   6.71
 29.83  13.86   3.62 ||   0.00   0.95   1.62 |   0.00   0.77   1.30 ||   0.54   7.11   7.08 |   0.30   6.80   6.66
 29.86  14.39   3.80 ||   0.00   0.91   1.60 |   0.00   0.74   1.29 ||   0.44   6.88   7.03 |   0.24   6.58   6.62
 30.07  14.94   3.99 ||   0.00   0.88   1.59 |   0.00   0.72   1.28 ||   0.36   6.65   6.98 |   0.20   6.36   6.57
^C
Peak values:  avg10  avg60 avg300
-----------  ------ ------ ------
some cpu      30.07  14.94   3.99
-----------  ------ ------ ------
some memory    0.00   1.05   1.65
full memory    0.00   0.85   1.33
-----------  ------ ------ ------
some io        0.81   7.79   7.21
full io        0.54   7.52   6.80

4aMgLn4 / nohang

nohang

What is the problem?

Solution

Features

Demo

Requirements

Memory and CPU usage

Warnings

Known problems

nohang vs nohang-desktop

How to install

To install on Fedora:

To install on RHEL 7 and RHEL 8:

For Arch Linux there's an AUR package

To install on Ubuntu 20.04/20.10

To install on Debian and Ubuntu-based systems:

To install on Gentoo and derivatives (e.g. Funtoo):

To install the latest version on any distro:

Command line options

How to configure

How to test nohang

Tasks state

Logging

oom-sort

psi-top

psi2log

Contribution

Documentation

License

About

Languages