nice - change process priority
#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
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 priority).
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 unprivileged 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 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 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 below.
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
circumstances. For details, see
sched(7).
POSIX.1 specifies that
nice() should return the new nice value. However,
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 provides
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),
setpriority(2),
capabilities(7),
sched(7)