The nice(1) command and the nice(2) function work as in previous versions of the UNIX system. They let you change the priority of a time-sharing process. Use lower numeric values to assign higher time-sharing priorities with these functions.
To change the scheduler class of a process or to specify a real-time priority, you must use one of the priocntl functions. Use higher numeric values to assign higher priorities with the priocntl(2) functions.