NICE(2) Linux Programmer's Manual NICE(2)
nice - change process priority
int nice(int inc);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
nice() 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
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.
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.
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).)
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
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
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.
nice(1), renice(1), fork(2), getpriority(2), getrlimit(2), setprior-
ity(2), capabilities(7), sched(7)
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Linux 2017-09-15 NICE(2)