.\" 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 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

nice \- change process priority

.SH SYNOPSIS

.B #include <unistd.h>

.PP

.BI "int nice(int " inc );

.PP

.in -4n

Feature Test Macro Requirements for glibc (see

.BR feature_test_macros (7)):

.in

.PP

.BR nice ():

_XOPEN_SOURCE

    || /* Since glibc 2.19: */ _DEFAULT_SOURCE

    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

.SH DESCRIPTION

.BR nice ()

adds

.I inc

to the nice value for the calling thread.

(A higher nice value means a low priority.)

.PP

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.

.PP

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

.BR RLIMIT_NICE

soft limit; see

.BR getrlimit (2)

for details.

.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.

.PP

A successful call can legitimately return \-1.

To detect an error, set

.I errno

to 0 before the call, and check whether it is nonzero after

.BR nice ()

returns \-1.

.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

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.

.\" SVr4 documents an additional

.\" .B EINVAL

.\" error code.

.SH NOTES

For further details on the nice value, see

.BR sched (7).

.PP

.IR 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

.BR sched (7).

.\"

.SS C library/kernel differences

POSIX.1 specifies that

.BR nice ()

should return the new nice value.

However, the raw Linux system call returns 0 on success.

Likewise, the

.BR nice ()

wrapper function provided in glibc 2.2.3 and earlier returns 0 on success.

.PP

Since glibc 2.2.4, the

.BR nice ()

wrapper function provided by glibc provides conformance to POSIX.1 by calling

.BR getpriority (2)

to obtain the new nice value, which is then returned to the caller.

.SH SEE ALSO

.BR nice (1),

.BR renice (1),

.BR fork (2),

.BR getpriority (2),

.BR getrlimit (2),

.BR setpriority (2),

.BR capabilities (7),

.BR sched (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.