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

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 parame-
       ters 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() function 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 call-
       ing process.

       The  conditions under which one process has the appropriate privilege to change the sched-
       uling 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  inclu-
       sive  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 con-
       tention 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-sched-
       uled entities for the system contention scope threads shall not be affected by these func-
       tions.

       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 con-
	      tained 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 sched-
	      uling parameters or the scheduling 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, Copyright (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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003			    SCHED_SETSCHEDULER(P)
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