sched_setscheduler, sched_getscheduler — set and get scheduling policy/parameters


#include <sched.h>
int sched_setscheduler( pid_t pid,
  int policy,
  const struct sched_param *param);
int sched_getscheduler( pid_t pid);


The sched_setscheduler() system call sets both the scheduling policy and parameters for the thread whose ID is specified in pid. If pid equals zero, the scheduling policy and parameters of the calling thread will be set.

The scheduling parameters are specified in the param argument, which is a pointer to a structure of the following form:

struct sched_param {
    int sched_priority;

In the current implementation, the structure contains only one field, sched_priority. The interpretation of param depends on the selected policy.

Currently, Linux supports the following "normal" (i.e., non-real-time) scheduling policies as values that may be specified in policy:


the standard round-robin time-sharing policy;


for "batch" style execution of processes; and


for running very low priority background jobs.

For each of the above policies, param−>sched_priority must be 0.

Various "real-time" policies are also supported, for special time-critical applications that need precise control over the way in which runnable threads are selected for execution. For the rules governing when a process may use these policies, see sched(7). The real-time policies that may be specified in policy are:


a first-in, first-out policy; and


a round-robin policy.

For each of the above policies, param−>sched_priority specifies a scheduling priority for the thread. This is a number in the range returned by calling sched_get_priority_min(2) and sched_get_priority_max(2) with the specified policy. On Linux, these system calls return, respectively, 1 and 99.

Since Linux 2.6.32, the SCHED_RESET_ON_FORK flag can be ORed in policy when calling sched_setscheduler(). As a result of including this flag, children created by fork(2) do not inherit privileged scheduling policies. See sched(7) for details.

sched_getscheduler() returns the current scheduling policy of the thread identified by pid. If pid equals zero, the policy of the calling thread will be retrieved.


On success, sched_setscheduler() returns zero. On success, sched_getscheduler() returns the policy for the thread (a nonnegative integer). On error, both calls return −1, and errno is set to indicate the error.



Invalid arguments: pid is negative or param is NULL.


(sched_setscheduler()) policy is not one of the recognized policies.


(sched_setscheduler()) param does not make sense for the specified policy.


The calling thread does not have appropriate privileges.


The thread whose ID is pid could not be found.


POSIX.1-2001, POSIX.1-2008 (but see BUGS below). The SCHED_BATCH and SCHED_IDLE policies are Linux-specific.


Further details of the semantics of all of the above "normal" and "real-time" scheduling policies can be found in the sched(7) manual page. That page also describes an additional policy, SCHED_DEADLINE, which is settable only via sched_setattr(2).

POSIX systems on which sched_setscheduler() and sched_getscheduler() are available define _POSIX_PRIORITY_SCHEDULING in <unistd.h>

POSIX.1 does not detail the permissions that an unprivileged thread requires in order to call sched_setscheduler(), and details vary across systems. For example, the Solaris 7 manual page says that the real or effective user ID of the caller must match the real user ID or the save set-user-ID of the target.

The scheduling policy and parameters are in fact per-thread attributes on Linux. The value returned from a call to gettid(2) can be passed in the argument pid. Specifying pid as 0 will operate on the attributes of the calling thread, and passing the value returned from a call to getpid(2) will operate on the attributes of the main thread of the thread group. (If you are using the POSIX threads API, then use pthread_setschedparam(3), pthread_getschedparam(3), and pthread_setschedprio(3), instead of the sched_*(2) system calls.)


POSIX.1 says that on success, sched_setscheduler() should return the previous scheduling policy. Linux sched_setscheduler() does not conform to this requirement, since it always returns 0 on success.


chrt(1), nice(2), sched_get_priority_max(2), sched_get_priority_min(2), sched_getaffinity(2), sched_getattr(2), sched_getparam(2), sched_rr_get_interval(2), sched_setaffinity(2), sched_setattr(2), sched_setparam(2), sched_yield(2), setpriority(2), capabilities(7), cpuset(7), sched(7)


This page is part of release 5.11 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at−pages/.

  Copyright (C) 2014 Michael Kerrisk <>

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.