PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult 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() 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 calling process.

       The conditions under which one process has appropriate privileges 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 the scheduling policy of the process, or the scheduling
       policy of another process, 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.

       See Scheduling Policies for a description on how this function affects  the  scheduling  of  the  threads
       within the target process.

       If  the  current scheduling policy for the target process is not SCHED_FIFO, SCHED_RR, or SCHED_SPORADIC,
       the result is implementation-defined; this case includes the SCHED_OTHER 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.  It  is  unspecified  whether  the  sched_ss_repl_period  and
       sched_ss_init_budget  values  are  stored  as  provided by this function or are rounded to align with the
       resolution of the clock being used.

       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 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

       Scheduling Policies, sched_getparam(), sched_getscheduler(), sched_setparam()

       The Base Definitions volume of POSIX.1‐2017, <sched.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 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.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .