Ubuntu – How to identify and kill hanging process, when system hangs and reacts slowly on user input

process

Recently when I tried to open a video with VLC, my system slowed down, the open applications webbrowser, VLC and filemanager and others didn't react any longer. The mouse just reacted still very slowly.

On a windows machine i would press a keycombi CTRL-ALT-DEL to open the taskmanager, search the process which caused the hang and kill it.

Since i'm fairly new with the use of linux i haven't figured out the best practice for solve such a situation in Ubuntu.

Which quick and effective way would you recommend to identify the hanging process and close it, when the system already reacts very slowly on user input?

Best Answer

There are two primary ways to identify hung processes. One is via the System Monitor GUI and the other is via top in command-line.

System Monitor

This can be found in System > Administration

account

You can also create a keyboard shortcut for this in this article.

Once the GUI launches you can select the Processes tab which will list all the running processes. Sort by the CPU column to find the most CPU intensive task

cpu

Lastly you can right click that task and choose to end it, stop it, or kill it. Killing it will immediately stop and remove that process from the system.

kill

Command-Line

If you have a terminal open you can simply type top this will list all the running processes similar to that of the Processes tab in the GUI

top

Within top it is CPU sorted by default - so the top most CPU intensive tasks are at the top. At anytime you can press the letter k to kill a process

Simply type the PID of the process you wish to kill and press enter. It will ask for a Kill signal to send. To kill the process nicely use the default 15 - to kill it right away "Do not pass go, do not collect $200" use 9.

sigkill

The process will then be terminated.

If you are experiencing sluggish interface you can try to SSH in remotely if that is enabled - or switch to a virtual console via Ctrl+Alt+F# Where F# is a Function Key (F3, F4, F5, etc). To return to the Desktop environment switch to either F7 or F8 depending on your version of Ubuntu.

Related Solutions

Ubuntu – In System monitor, what is the difference between Kill Process and End Process

Per the System Monitor manual, you should normally use "End Process", and only if that fails use "Kill Process":

You usually terminate a process only if you cannot end the process normally as described in To End a Process.

On a technical level this makes me think that End Process sends a SIGQUIT, which allows the process to trap and perform cleanup if needed, but if that fails, Kill Process should send a SIGKILL which should violently terminate the process, without chance of recovery. Use sparingly!

Ubuntu – How to identify the process locking a file

There is the infamous lsof:

sudo lsof /var/lib/dpkg/lock
COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF   NODE NAME
aptitude 4974 root    3uW  REG   8,23        0 815673 /var/lib/dpkg/lock

In this case aptitude is using the file. You should use root in case you are not sure which user is locking the file. It's useful for a bunch of things too, sadly it doesn't come installed with Ubuntu, so you have to install it first.

For the rest of mortals, there's the fuser command. This is peculiar since it only returns the PID instead of the name of the process:

➜  ~  sudo fuser /var/lib/dpkg/lock
/var/lib/dpkg/lock:   4974

Here it says that the file and PID, which is 4974, so we must investigate who is:

➜  ~  ps 4974
  PID TTY      STAT   TIME COMMAND
 4974 pts/1    Sl+    0:06 aptitude