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