How to Adjust Process Niceness (priority) on Most Linux Distributions

In GNU/Linux systems, "niceness" is used to define the CPU priority of a process. Essentially, it is the opposite of priority. So the nicer a process is, the less priority it has and vice versa. It is useful to adjust the niceness of a process, for example, when a non-important program is hindering CPU performance. By default, all processes have a niceness of 0. The niceness scale goes from -20 to 19.

As a non-root user, you can only increase niceness of processes you own. Root privileges are required to decrease the niceness of any process.

In this article, I will assume that you have root privileges (either logged in as the root user, or using sudo).

Show niceness of a process

In htop and top, niceness is listed for each process under the "NI" field:

root@demo:~# top
PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                                                   
 1 root      20   0   56892   6580   5216 S   0.0  1.3   0:01.09 systemd                                                                                                                          
 2 root      20   0       0      0      0 S   0.0  0.0   0:00.00 kthreadd                                                                                                                  
 3 root      20   0       0      0      0 S   0.0  0.0   0:00.00 ksoftirqd/0                                                                                                               
 5 root       0 -20       0      0      0 S   0.0  0.0   0:00.00 kworker/0:0H                                                                                                              
 7 root      20   0       0      0      0 S   0.0  0.0   0:00.07 rcu_sched        

Start a process with a specific niceness value

You can use the nice command to execute a command with a niceness value of your choice. For example:

nice -n 10 apt upgrade

This would run apt upgrade but with a niceness of 10, instead of the default value of 0.

The general format of the command above is as follows:

nice -n NICENESS COMMAND

Where NICENESS is any number between -20 and 19, and COMMAND is any command you would normally type in a shell.

Change niceness of a process

To modify the nice value of a process that is already running you would use renice. For example:

root@demo:~# renice -10 -p 564
564 (process ID) old priority 0, new priority -10

This command re-assigns a nice value of -10 to the process with the PID 564. The general format is as follows:

renice NICENESS -p PID

Where NICENESS is any number between -20 and 19, and PID is the process ID of the targeted process.