nice - change priority of a time-sharing process
int nice(int incr);
nice allows a process in the time-sharing scheduling class to change its
priority. The sched_setscheduler and schedctl system calls are more
general interfaces to scheduler functions.
nice adds the value of incr to the nice value of the calling process. A
process's nice value is a non-negative number for which a more positive
value results in lower CPU priority.
A maximum nice value of 39 and a minimum nice value of 0 are imposed by
the system. (The default nice value is 20.) Requests for values above
or below these limits result in the nice value being set to the
EPERM nice fails and does not change the nice value if incr is
negative or greater than 40 and the effective user ID of
the calling process is not super-user.
EINVAL nice fails if called by a process in a scheduling class
other than time-sharing.
exec(2), setpriority(2), sched_setscheduler(2). schedctl(2).
csh(1), sh(1), nice(1).
Upon successful completion, nice returns the new nice value minus 20.
Otherwise, a value of -1 is returned and errno is set to indicate the
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