/usr/ucb/renice priority pid ...
/usr/ucb/renice priority [-p pid ...] [-g pgrp ...] [-u username ...]
Users other than the privileged user may only alter the priority of processes they own, and can only monotonically increase their nice value within the range 0 to 20. This prevents overriding administrative fiats. The privileged user may alter the priority of any process and set the priority to any value in the range -20 to 20. Useful priorities are: 19 (the affected processes will run only when nothing else in the system wants to), 0 (the base scheduling priority) and any negative value (to make things go very fast).
If only the priority is specified, the current process (alternatively, process group or user) is used.
To regain control you must make the priority greater than zero.
Users other than the privileged user cannot increase scheduling priorities of their own processes, even if they were the ones that decreased the priorities in the first place.
The priocntl command subsumes the function of renice.