NAME

       sched_setscheduler, sched_getscheduler - set and get scheduling policy/parameters

SYNOPSIS

       #include <sched.h>

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

       int sched_getscheduler(pid_t pid);

DESCRIPTION

       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

       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

       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

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

NOTES

       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

       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

       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

       This page is part of release 5.10 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/.