linux: renice

from : http://linux.about.com/library/cmd/blcmdl8_renice.htm

Users other than the super-user may only alter the priority of processes they own, and can only monotonically increase their ``nice value'' within the range 0 to PRIO_MAX (20). (This prevents overriding administrative fiats.) The super-user may alter the priority of any process and set the priority to any value in the range PRIO_MIN (-20) to PRIO_MAX Useful priorities are: 20 (the affected processes will run only when nothing else in the system wants to), 0 (the ``base'' scheduling priority), anything negative (to make things go very fast).