sched_setscheduler(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON

SCHED_SETSCHEDULER(2)   Linux Programmer's Manual  SCHED_SETSCHEDULER(2)

NAME         top

       sched_setscheduler, sched_getscheduler - set and get scheduling
       policy/parameters

SYNOPSIS         top

       #include <sched.h>

       int sched_setscheduler(pid_t pid, int policy,
                              const struct sched_param *param);
       int sched_getscheduler(pid_t pid);

DESCRIPTION         top

       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:

       SCHED_OTHER
              the standard round-robin time-sharing policy;

       SCHED_BATCH
              for "batch" style execution of processes; and

       SCHED_IDLE
              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:

       SCHED_FIFO
              a first-in, first-out policy; and

       SCHED_RR
              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.

RETURN VALUE         top

       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.

ERRORS         top

       EINVAL Invalid arguments: pid is negative or param is NULL.

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

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

       EPERM  The calling thread does not have appropriate privileges.

       ESRCH  The thread whose ID is pid could not be found.

CONFORMING TO         top

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

NOTES         top

       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.)

BUGS         top

       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.

SEE ALSO         top

       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)

COLOPHON         top

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

Linux                          2021-03-22          SCHED_SETSCHEDULER(2)

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