The scheduling priority of the process is augmented by incr. Positive priorities get less service than normal. Priority 10 is recommended to users who wish to execute long-running
programs without undue impact on system performance.
Negative increments are illegal, except when specified by the privileged user. The priority is limited to the range -20 (most urgent) to 20 (least). Requests for values above or below these
limits result in the scheduling priority being set to the corresponding limit.
The priority of a process is passed to a child process by fork(2).
For a privileged process to return to normal priority from an unknown state, nice() should be called successively with arguments -40 (goes to priority -20 because of truncation),
20 (to get to 0), then 0 (to maintain compatibility with previous versions of this call).
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