getpriority(2) — Linux manual page
getpriority(2) — Linux manual page
https://man7.org/linux/man-pages/man2/setpriority.2.html
| NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | BUGS | SEE ALSO | COLOPHON |
getpriority(2) System Calls Manual getpriority(2) NAME top getpriority, setpriority - get/set program scheduling priority LIBRARY top Standard C library (libc, -lc) SYNOPSIS top #include <sys/resource.h>
int getpriority(int which, id_t who);
int setpriority(int which, id_t who, int prio); DESCRIPTION top
The scheduling priority of the process, process group, or user, as
indicated by which and who is obtained with the getpriority() call
and set with the 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).
The value which is one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER,
and who is interpreted relative to which (a process identifier for
PRIO_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.
The 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.
The getpriority() call 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 details. RETURN VALUE top
On success, getpriority() returns the calling thread's nice value,
which may be a negative number. On error, it returns -1 and sets
errno to indicate the error.
Since a successful call to getpriority() can legitimately return
the value -1, it is necessary to clear errno prior to the call,
then check errno afterward to determine if -1 is an error or a
legitimate value.
setpriority() returns 0 on success. On failure, it returns -1 and
sets errno to indicate the error. ERRORS top
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 CAP_SYS_NICE
capability).
EINVAL which was not one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER.
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
CAP_SYS_NICE capability). But see HISTORY below.
ESRCH No process was located using the which and who values
specified. STANDARDS top
POSIX.1-2024. HISTORY top
POSIX.1-2001, SVr4, 4.4BSD (these interfaces first appeared in
4.2BSD).
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 Linux
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 the process
who. 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. NOTES top
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).
A child created by fork(2) inherits its parent's nice value. The
nice value is preserved across execve(2).
C library/kernel differences The getpriority system call returns nice values translated to the range 40..1, since a negative return value would be interpreted as an error. The glibc wrapper function for getpriority() translates the value back according to the formula unice = 20 - knice (thus, the 40..1 range returned by the kernel corresponds to the range -20..19 as seen by user space). BUGS top 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 behaviour, which may be made standards conformant in the future. SEE ALSO top nice(1), renice(1), fork(2), capabilities(7), sched(7)
Documentation/scheduler/sched-nice-design.txt in the Linux kernel
source tree (since Linux 2.6.23) COLOPHON top
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Linux man-pages 6.16 2025-10-29 getpriority(2) Pages that refer to this page: renice(1), getrlimit(2), ioprio_set(2), nice(2), sched_rr_get_interval(2), sched_setaffinity(2), sched_setattr(2), sched_setparam(2), sched_setscheduler(2), syscalls(2), errno(3), id_t(3type), proc_pid_stat(5), systemd.exec(5), capabilities(7), credentials(7), pid_namespaces(7), pthreads(7), sched(7)
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