SCHED_SETSCHEDULER(3P)                              POSIX Programmer's Manual                             SCHED_SETSCHEDULER(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       sched_setscheduler - set scheduling policy and parameters (REALTIME)

SYNOPSIS
       #include <sched.h>

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


DESCRIPTION
       The  sched_setscheduler()  function shall set the scheduling policy and scheduling parameters of the process specified by
       pid to policy and the parameters specified in the sched_param structure pointed to by param, respectively. The  value  of
       the  sched_priority  member in the sched_param structure shall be any integer within the inclusive priority range for the
       scheduling policy specified by policy.  If the value of pid is negative, the behavior of the  sched_setscheduler()  func-
       tion is unspecified.

       The possible values for the policy parameter are defined in the <sched.h> header.

       If  a  process  specified  by pid exists, and if the calling process has permission, the scheduling policy and scheduling
       parameters shall be set for the process whose process ID is equal to pid.

       If pid is zero, the scheduling policy and scheduling parameters shall be set for the calling process.

       The conditions under which one process has the appropriate privilege to  change  the  scheduling  parameters  of  another
       process are implementation-defined.

       Implementations  may require that the requesting process have permission to set its own scheduling parameters or those of
       another process. Additionally, implementation-defined restrictions may apply as to the appropriate privileges required to
       set a process' own scheduling policy, or another process' scheduling policy, to a particular value.

       The  sched_setscheduler()  function  shall  be  considered successful if it succeeds in setting the scheduling policy and
       scheduling parameters of the process specified by pid to the values specified by policy and the structure pointed  to  by
       param, respectively.

       If  the  scheduling policy specified by policy is SCHED_SPORADIC, the value specified by the sched_ss_low_priority member
       of the param argument shall be any integer within the inclusive priority  range  for  the  sporadic  server  policy.  The
       sched_ss_repl_period  and  sched_ss_init_budget members of the param argument shall represent the time parameters used by
       the sporadic server scheduling policy for the target process. The sched_ss_max_repl member of the  param  argument  shall
       represent  the  maximum  number of replenishments that are allowed to be pending simultaneously for the process scheduled
       under this scheduling policy.

       The specified sched_ss_repl_period shall be greater than or equal to the specified sched_ss_init_budget for the  function
       to succeed; if it is not, then the function shall fail.

       The  value  of  sched_ss_max_repl  shall be within the inclusive range [1, {SS_REPL_MAX}] for the function to succeed; if
       not, the function shall fail.

       If  the  scheduling  policy  specified  by  policy  is  either  SCHED_FIFO  or   SCHED_RR,   the   sched_ss_low_priority,
       sched_ss_repl_period,  and  sched_ss_init_budget  members  of  the  param argument shall have no effect on the scheduling
       behavior.

       The effect of this function on individual threads is dependent on the scheduling contention scope of the threads:

        * For threads with system scheduling contention scope, these functions shall have no effect on their scheduling.

        * For threads with process scheduling contention scope, the threads' scheduling policy and associated  parameters  shall
          not  be affected. However, the scheduling of these threads with respect to threads in other processes may be dependent
          on the scheduling parameters of their process, which are governed using these functions.

       If an implementation supports a two-level scheduling model in which library threads are multiplexed  on  top  of  several
       kernel-scheduled  entities,  then  the underlying kernel-scheduled entities for the system contention scope threads shall
       not be affected by these functions.

       The underlying kernel-scheduled entities for the process contention scope threads shall have their scheduling policy  and
       associated  scheduling  parameters  changed  to  the values specified in policy and param, respectively. Kernel-scheduled
       entities for use by process contention scope threads that are created after  this  call  completes  shall  inherit  their
       scheduling policy and associated scheduling parameters from the process.

       This  function  is  not  atomic with respect to other threads in the process.  Threads may continue to execute while this
       function call is in the process of changing the scheduling policy and associated scheduling parameters for the underlying
       kernel-scheduled entities used by the process contention scope threads.

RETURN VALUE
       Upon  successful  completion,  the  function  shall  return the former scheduling policy of the specified process. If the
       sched_setscheduler() function fails  to  complete  successfully,  the  policy  and  scheduling  parameters  shall  remain
       unchanged, and the function shall return a value of -1 and set errno to indicate the error.

ERRORS
       The sched_setscheduler() function shall fail if:

       EINVAL The  value  of the policy parameter is invalid, or one or more of the parameters contained in param is outside the
              valid range for the specified scheduling policy.

       EPERM  The requesting process does not have permission to set either or both of the scheduling parameters or the schedul-
              ing policy of the specified process.

       ESRCH  No process can be found corresponding to that specified by pid.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       sched_getparam(), sched_getscheduler(), sched_setparam(), the Base Definitions volume of IEEE Std 1003.1-2001, <sched.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open  Group
       Standard   is   the   referee   document.   The   original   Standard   can   be   obtained  online  at  http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                        SCHED_SETSCHEDULER(3P)