Section (2) getpriority
getpriority, setpriority — get/set program scheduling priority
#include <sys/time.h> #include <sys/resource.h>
The scheduling priority of the process, process group, or
user, as indicated by
who is obtained with the
getpriority() call and set with
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 nice(2).
who is interpreted relative to
which (a process
process group identifier for
PRIO_PGRP, and a user ID for
PRIO_USER). A zero value for
who denotes (respectively) the
calling process, the process group of the calling process, or
the real user ID of the calling process.
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
returns the highest priority (lowest numerical value) enjoyed
by any of the specified processes. The
setpriority() call sets the priorities of
all of the specified processes to the specified value.
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
returns the calling thread_zsingle_quotesz_s nice value, which may be a
negative number. On error, it returns −1 and sets
errno to indicate the cause of
the error. Since a successful call to
getpriority() can legitimately return the
value −1, it is necessary to clear the external
errno prior to the
call, then check it afterward to determine if −1 is an
error or a legitimate value.
setpriority() returns 0 on
success. On error, it returns −1 and sets
errno to indicate the cause of the
whichwas not one of
No process was located using the
In addition to the errors indicated above,
setpriority() may fail if:
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
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
CAP_SYS_NICEcapability). But see NOTES below.
For further details on the nice value, see sched(7).
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).
The details on the condition for 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
who (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
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.
is not required these days, but increases portability.
> defines the
rusage structure with fields
of type struct timeval
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
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
unice = 20 −
knice. (Thus, the kernel_zsingle_quotesz_s 40..1 range
corresponds to the range −20..19 as seen by user
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.
in the Linux kernel source tree (since Linux 2.6.23)
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(#)getpriority.2 6.9 (Berkeley) 3/10/91
Modified 1993-07-24 by Rik Faith <faithcs.unc.edu>
Modified 1996-07-01 by Andries Brouwer <aebcwi.nl>
Modified 1996-11-06 by Eric S. Raymond <esrthyrsus.com>
Modified 2001-10-21 by Michael Kerrisk <mtk.manpagesgmail.com>
Corrected statement under EPERM to clarify privileges required
Modified 2002-06-21 by Michael Kerrisk <mtk.manpagesgmail.com>
Clarified meaning of 0 value for _zsingle_quotesz_who_zsingle_quotesz_ argument
Modified 2004-05-27 by Michael Kerrisk <mtk.manpagesgmail.com>