Linux nice/renice Command Summary

1. Nice command

The kernel determines how much processor time the process needs based on the nice value of the process. The value range for nice values is: 20 to 20. A process with a nice value of 20 has a high priority. A process with a nice value of 20 has a low priority.

1) Display the nice value of all running processes with PS Axl

# PS Axl

F UID PID PPID PRI NI VSZ RSS wchan STAT TTY time COMMAND

4 0 1 0 0 2172 552-s? 0:17 Init [5]

1 0 3 1 0 0 ksofti SN? 3:18 [ksoftirqd/0]

1 0 1 5-10 0 0 worker s<? 0:01 [events/0]

4 0 5145 1 32124 18592-sns? 0:08/usr/bin/python/usr/bin/rhn-applet-gui--sm-client-id DEFAULT4

4 0 5147 5142 0 3528 604-s? 0:00/sbin/pam_timestamp_check-d Root

1 503 17552 4180 0 14208 3920-s? 0:01/home/www/apache2/bin/httpd-f/home/www/apache2/conf/httpd.conf-k Start

2) How to assign a low priority to a shell script (a higher nice value)?

In the following example, when I launch the nice-test.sh script in the background, the nice value is 0.

$./nice-test.sh &

[3] 13009

$ ps Axl | grep nice-test

0 509 13009 12863 0 4652 972 wait S pts/1 0:00/bin/bash./nice-test.sh

[Note: The sixth column is a nice value of 0]

Now execute the same script with a different nice value, as follows:

$ nice-10./nice-test.sh &

[1] 13016

$ ps Axl | grep nice-test

0 509 13016 12863 4236 968 wait SN pts/1 0:00/bin/bash./nice-test.sh

[Note: The sixth column of value 10 is the nice value of the shell script]

3) How to assign a high priority (lower nice value) to a shell script?

In the example below, the nice value assigned to the shell script nice-test.sh a "-10".

$ nice--10./nice-test.sh &

[1] 13021

$ nice:cannot Set Priority:permission denied

Note: Only the root user can set a negative nice value. Try again with the root user login. Note that there is a double dash in front of 10 in the Nice command below.

# nice--10./nice-test.sh &

[1] 13060

# PS Axl | grep nice-test

4 0 13060 13024 10-10 5388 964 wait s< pts/1 0:00/bin/bash./nice-test.sh

[Note: The Sixth column value is-10 is the nice value of the shell script]

2. Renice command

Renice can set the scheduling priority for a running process.

1) How to lower the priority of a running process (add nice value)?

In the following example, an existing shell script runs with a nice value of 10. (6th column of PS output)

$ ps Axl | grep nice-test

0 509 13245 13216 5244 968 wait SN pts/1 0:00/bin/bash./nice-test.sh

To increase the Nice value (and therefore lower the priority), execute the renice command as follows.

$ renice 16-p 13245

13245:old priority Ten, new priority 16

$ ps Axl | grep nice-test

0 509 13245 13216 5244 968 wait SN pts/1 0:00/bin/bash./nice-test.sh

[Note: Now, the 6th column of nice-test.sh (PID 13245) shows that the new nice value is 16]

2) How to increase the priority of the running process (reduce the nice value)?

In the following example, an existing shell script runs with a nice value of 10. (PS output 6th column)

$ ps Axl | grep nice-test

0 509 13254 13216 4412 968 wait SN pts/1 0:00/bin/bash./nice-test.sh

To elevate its priority, give it a lower nice value. However, only root can increase the priority of the running process, or you will get the following error message.

$ renice 5-p 13254

Renice:13254:setpriority:permission denied

Login as root to increase the priority of a running

Process

$ Su-

# Renice 5-p 13254

13254:old priority Ten, new priority 5

# PS Axl | grep nice-test

0 509 13254 13216 5 4412 968 wait SN pts/1 0:00/bin/bash./nice-test.sh

Note: The 6th column now shows a lower nice value of 5 (elevation priority)]