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[thirdparty/man-pages.git] / man2 / nice.2

.\" Copyright (c) 1992 Drew Eckhardt <drew@cs.colorado.edu>, March 28, 1992
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.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1996-11-04 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 2001-06-04 by aeb
.\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.TH NICE 2 2007-07-26 "Linux" "Linux Programmer's Manual"
.SH NAME
nice \- change process priority
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.BI "int nice(int " inc );
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR nice ():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
.SH DESCRIPTION
.BR nice ()
adds
.I inc
to the nice value for the calling process.
(A higher nice value means a low priority.)
Only the super\%user may specify a negative increment,
or priority increase.
The range for nice values is described in
.BR getpriority (2).
.SH RETURN VALUE
On success, the new nice value is returned (but see NOTES below).
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EPERM
The calling process attempted to increase its priority by
supplying a negative
.I inc
but has insufficient privileges.
Under Linux the
.B CAP_SYS_NICE
capability is required.
(But see the discussion of the
.B RLIMIT_NICE
resource limit in
.BR setrlimit (2).)
.SH CONFORMING TO
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
.B EINVAL
error code.
.SH NOTES
SUSv2 and POSIX.1-2001 specify that
.BR nice ()
should return the new nice value.
However, the Linux syscall and the
.BR nice ()
library function provided in older versions of (g)libc
(earlier than glibc 2.2.4) return 0 on success.
The new nice value can be found using
.BR getpriority (2).

Since glibc 2.2.4,
.BR nice ()
is implemented as a library function that calls
.BR 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
.I errno
to 0 before the call, and check its value when
.BR nice ()
returns \-1.
.SH SEE ALSO
.BR nice (1),
.BR renice (1),
.BR fork (2),
.BR getpriority (2),
.BR setpriority (2),
.BR capabilities (7)