Use nice and renice commands. -20 highest priority, 19 lowest.

The default value of all the processes is 0.

nice -n 19 ./process_intensive_task

This will set the priority of process id no 123 to -1.

renice -1 123

This will set the priority of process id no 2345 to -4, which will in turn increase its priority over others.

renice -4 -p 2345 

This will set the priority of the process id 3456 to 13, and all the process owned by user “john” to the priority of 15.

renice 13 -p 3456 -u john 15

This will set all process owned by “john”,“peter” and also the group “custom” to 14.

renice 14 -u john,peter -g custom