.\" Copyright (c) 1980, 1991 The Regents of the University of California.

.\" All rights reserved.

.\"

.\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)

.\" Redistribution and use in source and binary forms, with or without

.\" modification, are permitted provided that the following conditions

.\" are met:

.\" 1. Redistributions of source code must retain the above copyright

.\"    notice, this list of conditions and the following disclaimer.

.\" 2. Redistributions in binary form must reproduce the above copyright

.\"    notice, this list of conditions and the following disclaimer in the

.\"    documentation and/or other materials provided with the distribution.

.\" 3. All advertising materials mentioning features or use of this software

.\"    must display the following acknowledgement:

.\"	This product includes software developed by the University of

.\"	California, Berkeley and its contributors.

.\" 4. Neither the name of the University nor the names of its contributors

.\"    may be used to endorse or promote products derived from this software

.\"    without specific prior written permission.

.\"

.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND

.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE

.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

.\" SUCH DAMAGE.

.\" %%%LICENSE_END

.\"

.\"     @(#)getpriority.2	6.9 (Berkeley) 3/10/91

.\"

.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>

.\" Modified 1996-07-01 by Andries Brouwer <aeb@cwi.nl>

.\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>

.\" Modified 2001-10-21 by Michael Kerrisk <mtk.manpages@gmail.com>

.\"    Corrected statement under EPERM to clarify privileges required

.\" Modified 2002-06-21 by Michael Kerrisk <mtk.manpages@gmail.com>

.\"    Clarified meaning of 0 value for 'who' argument

.\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>

.\"

.TH GETPRIORITY 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

getpriority, setpriority \- get/set program scheduling priority

.SH SYNOPSIS

.B #include <sys/time.h>

.br

.B #include <sys/resource.h>

.PP

.BI "int getpriority(int " which ", id_t " who );

.br

.BI "int setpriority(int " which ", id_t " who ", int " prio );

.SH DESCRIPTION

The scheduling priority of the process, process group, or user, as

indicated by

.I which

and

.I who

is obtained with the

.BR getpriority ()

call and set with the

.BR setpriority ()

call.

The process attribute dealt with by these system calls is

the same attribute (also known as the "nice" value) that is dealt with by

.BR nice (2).

.PP

The value

.I which

is one of

.BR PRIO_PROCESS ,

.BR PRIO_PGRP ,

or

.BR PRIO_USER ,

and

.I who

is interpreted relative to

.I which

(a process identifier for

.BR PRIO_PROCESS ,

process group

identifier for

.BR PRIO_PGRP ,

and a user ID for

.BR PRIO_USER ).

A zero value for

.I who

denotes (respectively) the calling process, the process group of the

calling process, or the real user ID of the calling process.

.PP

The

.I prio

argument is a value in the range \-20 to 19 (but see NOTES below).

with \-20 being the highest priority and 19 being the lowest priority.

Attempts to set a priority outside this range

are silently clamped to the range.

The default priority is 0;

lower values give a process a higher scheduling priority.

.PP

The

.BR getpriority ()

call returns the highest priority (lowest numerical value)

enjoyed by any of the specified processes.

The

.BR setpriority ()

call sets the priorities of all of the specified processes

to the specified value.

.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,

.BR getpriority ()

returns the calling thread's nice value, which may be a negative number.

On error, it returns \-1 and sets

.I errno

to indicate the cause of the error.

Since a successful call to

.BR getpriority ()

can legitimately return the value \-1, it is necessary

to clear the external variable

.I errno

prior to the

call, then check it afterward to determine

if \-1 is an error or a legitimate value.

.PP

.BR setpriority ()

returns 0 on success.

On error, it returns \-1 and sets

.I errno

to indicate the cause of the error.

.SH ERRORS

.TP

.B EINVAL

.I which

was not one of

.BR PRIO_PROCESS ,

.BR PRIO_PGRP ,

or

.BR PRIO_USER .

.TP

.B ESRCH

No process was located using the

.I which

and

.I who

values specified.

.PP

In addition to the errors indicated above,

.BR setpriority ()

may fail if:

.TP

.B EACCES

The caller attempted to set a lower nice value

(i.e., a higher process priority), but did not

have the required privilege (on Linux: did not have the

.B CAP_SYS_NICE

capability).

.TP

.B EPERM

A process was located, but its effective user ID did not match

either the effective or the real user ID of the caller,

and was not privileged (on Linux: did not have the

.B CAP_SYS_NICE

capability).

But see NOTES below.

.SH CONFORMING TO

POSIX.1-2001, POSIX.1-2008,

SVr4, 4.4BSD (these interfaces first appeared in 4.2BSD).

.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).

.PP

A child created by

.BR fork (2)

inherits its parent's nice value.

The nice value is preserved across

.BR execve (2).

.PP

The details on the condition for

.B EPERM

depend on the system.

The above description is what POSIX.1-2001 says, and seems to be followed on

all System\ V-like systems.

Linux kernels before 2.6.12 required the real or

effective user ID of the caller to match

the real user of the process \fIwho\fP (instead of its effective user ID).

Linux 2.6.12 and later require

the effective user ID of the caller to match

the real or effective user ID of the process \fIwho\fP.

All BSD-like systems (SunOS 4.1.3, Ultrix 4.2,

4.3BSD, FreeBSD 4.3, OpenBSD-2.5, ...) behave in the same

manner as Linux 2.6.12 and later.

.PP

Including

.I <sys/time.h>

is not required these days, but increases portability.

(Indeed,

.I <sys/resource.h>

defines the

.I rusage

structure with fields of type

.I struct timeval

defined in

.IR <sys/time.h> .)

.\"

.SS C library/kernel differences

Within the kernel, nice values are actually represented

using the range 40..1

(since negative numbers are error codes) and these are the values

employed by the

.BR setpriority ()

and

.BR getpriority ()

system calls.

The glibc wrapper functions for these system calls handle the

translations between the user-land and kernel representations

of the nice value according to the formula

.IR "unice\ =\ 20\ \-\ knice" .

(Thus, the kernel's 40..1 range corresponds to the

range \-20..19 as seen by user space.)

.SH BUGS

According to POSIX, the nice value is a per-process setting.

However, under the current Linux/NPTL implementation of POSIX threads,

the nice value is a per-thread attribute:

different threads in the same process can have different nice values.

Portable applications should avoid relying on the Linux behavior,

which may be made standards conformant in the future.

.SH SEE ALSO

.BR nice (1),

.BR renice (1),

.BR fork (2),

.BR capabilities (7),

.BR sched (7)

.PP

.I Documentation/scheduler/sched-nice-design.txt

in the Linux kernel source tree (since Linux 2.6.23)

.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/.