nice command is used to modify scheduling priority of some running command or application. If we give a process a higher priority, then Kernel will allocate more CPU time to that process.
There are two terms which one should pay attention.
Priority Value :
The priority value is the process’s actual priority which is used by the Linux kernel to schedule a task.
In Linux system priorities are 0 to 139 in which 0 to 99 for real-time and 100 to 139 for users.
Nice Value :
Nice values are user-space values that we can use to control the priority of a process. The nice value range is -20 to +19 where -20 is highest, 0 default and +19 is lowest.
The relation between nice value and priority is as such –
Priority_Value = Nice_Value + 20
In above picture you can see both – Priority and Nice Level.
You can also check the same with
# ps -elx
■ Setting Priority of running process
# nice -10 /usr/sbin/httpd
■ Assign negative Priority of running process
# nice --10 /usr/sbin/httpd
■ Change nice level of running process.
# renice -n 15 -p 1260 1260 (process ID) old priority 0, new priority 15