[tlug] Tip of the Day: My system is slow because of some big process (so I want to change its priority)

["Josh Glover" <jmglov@example.com>]

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                       This TotD is also available in the wiki:

http://tlug.jp/wiki/Linux_Help:Tip_of_the_Day:My_system_is_slow_because_of_some_big_process_%28so_I_want_to_change_its_priority%29
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If you started some big hungry process (e.g. backing up a DVD) and now
your system is not responsive enough for your Firefox / XEmacs /
GQview / jUploadr workload, simply drop (well, "raise", in UNIX Land)
the priority of the CPU hogging process:

  1. Identify the process ID of the hog:

     ps -u "${USER}" -O pcpu --sort pcpu | sed -e 1d | sort -nr -k 2 | head

     See #Identifying the Process for an explanation
  2. Change the priority of the process:

     PID=<pid> # where <pid> is process ID from the previous step
     NICENESS=10 # or change 10 to any integer between 1 and 20, inclusive
     renice +${NICENESS} ${PID}

Your system should get noticeably more responsive!

See man 8 renice for more details.


[edit]
Identifying the Process

Here is a breakdown of the pipeline (Wikipedia) we used above:

  1.

     ps -u "${USER}" -O pcpu --sort pcpu

     (man 1 ps); show all processes for the current user, adding CPU
usage (percentage) to the default display columns, sorting by CPU
usage (percentage)
  2.

     sed -e 1d

     (man 1 sed); delete the first line (i.e. ps's header)
  3.

     sort -nr -k 2

     (man 1 sort); sort numerically in reverse (i.e. descending
order) on column 2
  4.

     head

     (man 1 head); display the first few lines only

--
Cheers,
Josh