Manpages - nice.2
Table of Contents
NAME
nice - 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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
*nice*() adds inc to the nice value for the calling thread. (A higher nice value means a lower 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.
RETURN VALUE
On success, the new nice value is returned (but see NOTES below). On error, -1 is returned, and errno is set to indicate the error.
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 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).)
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 circumstances. For details, see *sched*(7).
C library/kernel differences
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.
SEE ALSO
*nice*(1), *renice*(1), *fork*(2), *getpriority*(2), *getrlimit*(2), *setpriority*(2), *capabilities*(7), *sched*(7)
COLOPHON
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