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)):
nice(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
nice() adds inc to the nice value for the calling process. (A higher nice value means a
low priority.) Only the superuser may specify a negative increment, or priority increase.
The range for nice values is described in getpriority(2).
On success, the new nice value is returned (but see NOTES below). On error, -1 is
returned, and errno is set appropriately.
EPERM The calling process attempted to increase its priority by supplying 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 setr-
SVr4, 4.3BSD, POSIX.1-2001. However, the Linux and (g)libc (earlier than glibc 2.2.4)
return value is nonstandard, see below. SVr4 documents an additional EINVAL error code.
SUSv2 and POSIX.1-2001 specify that nice() should return the new nice value. However, the
Linux syscall and the nice() library function provided in older versions of (g)libc (ear-
lier than glibc 2.2.4) return 0 on success. The new nice value can be found using getpri-
Since glibc 2.2.4, nice() is implemented as a library function that calls getpriority(2)
to obtain the new nice value to be returned to the caller. With this implementation, a
successful call can legitimately return -1. To reliably detect an error, set errno to 0
before the call, and check its value when nice() returns -1.
nice(1), renice(1), fork(2), getpriority(2), setpriority(2), capabilities(7)
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Linux 2007-07-26 NICE(2)