NICE(2) Linux Programmer's Manual NICE(2)NAMEnice - change process priority
SYNOPSIS
#include <unistd.h>
int nice(int inc);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
nice(): _XOPEN_SOURCE
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTIONnice() adds inc to the nice value for the calling thread. (A higher
nice value means a low priority.)
The range of the nice value is +19 (low priority) to -20 (high prior‐
ity). Attempts to set a nice value outside the range are clamped to
the range.
Traditionally, only a privileged process could lower the nice value
(i.e., set a higher priority). However, since Linux 2.6.12, an unpriv‐
ileged process can decrease the nice value of a target process that has
a suitable RLIMIT_NICE soft limit; see getrlimit(2) for details.
RETURN VALUE
On success, the new nice value is returned (but see NOTES below). On
error, -1 is returned, and errno is set appropriately.
A successful call can legitimately return -1. To detect an error, set
errno to 0 before the call, and check whether it is nonzero after
nice() returns -1.
ERRORS
EPERM The calling process attempted to increase its priority by sup‐
plying a negative inc but has insufficient privileges. Under
Linux, the CAP_SYS_NICE capability is required. (But see the
discussion of the RLIMIT_NICE resource limit in setrlimit(2).)
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD. However, the raw system call
and (g)libc (earlier than glibc 2.2.4) return value is nonstandard, see
below.
NOTES
For further details on the nice value, see sched(7).
Note: the addition of the "autogroup" feature in Linux 2.6.38 means
that the nice value no longer has its traditional effect in many cir‐
cumstances. For details, see sched(7).
C library/kernel differences
POSIX.1 specifies that nice() should return the new nice value. How‐
ever, the raw Linux system call returns 0 on success. Likewise, the
nice() wrapper function provided in glibc 2.2.3 and earlier returns 0
on success.
Since glibc 2.2.4, the nice() wrapper function provided by glibc pro‐
vides conformance to POSIX.1 by calling getpriority(2) to obtain the
new nice value, which is then returned to the caller.
SEE ALSOnice(1), renice(1), fork(2), getpriority(2), getrlimit(2), setprior‐
ity(2), capabilities(7), sched(7)COLOPHON
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Linux 2017-09-15 NICE(2)
