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 pol‐
       icy/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
       appropriately.

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 sched(7).

       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 4.08 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                            2015-08-08            SCHED_SETSCHEDULER(2)