The Open Group Base Specifications Issue 7, 2018 edition
IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)
Copyright © 2001-2018 IEEE and The Open Group


sched_setparam - set scheduling parameters (REALTIME)


[PS] [Option Start] #include <sched.h>

int sched_setparam(pid_t
pid, const struct sched_param *param); [Option End]


The sched_setparam() function shall set the scheduling parameters of the process specified by pid to the values specified by the sched_param structure pointed to by param. The value of the sched_priority member in the sched_param structure shall be any integer within the inclusive priority range for the current scheduling policy of the process specified by pid. Higher numerical values for the priority represent higher priorities. If the value of pid is negative, the behavior of the sched_setparam() function is unspecified.

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

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

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

Implementations may require the requesting process to have appropriate privileges to set its own scheduling parameters or those of another process.

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, [SS] [Option Start] or SCHED_SPORADIC, [Option End]  the result is implementation-defined; this case includes the SCHED_OTHER policy.

[SS] [Option Start] 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. [Option End]

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 for the underlying kernel-scheduled entities used by the process contention scope threads.


If successful, the sched_setparam() function shall return zero.

If the call to sched_setparam() is unsuccessful, the priority shall remain unchanged, and the function shall return a value of -1 and set errno to indicate the error.


The sched_setparam() function shall fail if:

One or more of the requested scheduling parameters is outside the range defined for the scheduling policy of the specified pid.
The requesting process does not have permission to set the scheduling parameters for the specified process, or does not have appropriate privileges to invoke sched_setparam().
No process can be found corresponding to that specified by pid.

The following sections are informative.










Scheduling Policies, sched_getparam, sched_getscheduler, sched_setscheduler

XBD <sched.h>


First released in Issue 5. Included for alignment with the POSIX Realtime Extension.

Issue 6

The sched_setparam() function is marked as part of the Process Scheduling option.

The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Process Scheduling option.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

The SCHED_SPORADIC scheduling policy is added for alignment with IEEE Std 1003.1d-1999.

IEEE PASC Interpretation 1003.1 #100 is applied.

Issue 7

Austin Group Interpretation 1003.1-2001 #061 is applied, updating the DESCRIPTION.

Austin Group Interpretation 1003.1-2001 #119 is applied, clarifying the accuracy requirements for the sched_ss_repl_period and sched_ss_init_budget values.

End of informative text.


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