NAME
nice — change priority of a process
SYNOPSIS
#include <unistd.h>
int nice(int priority_change);
DESCRIPTION
nice()
adds the value of
priority_change
to the nice value of the calling process.
A process's
nice value
is a positive 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.
Requests for values above or below these limits result in the nice value
being set to the corresponding limit.
If the calling process contains more than one thread or
lightweight process (i.e., the
process is multi-threaded) this function shall apply to all threads or
lightweight processes in the calling process.
RETURN VALUE
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 error.
Note that
nice()
assumes a user process priority value of 20.
If a user
having appropriate privileges
has changed the user process priority value
to something less than 20, certain values for
priority_change
can cause
nice()
to return -1, which is indistinguishable from an error return.
ERRORS
- [EPERM]
nice()
fails and does not change the nice value if
priority_change
is negative or greater than 40, and the effective user
ID
of the calling process is not a user
having appropriate privileges.
STANDARDS CONFORMANCE
nice(): AES, SVID2, SVID3, XPG2, XPG3, XPG4
