The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> sched_setscheduler - set scheduling policy and parameters (REALTIME)

#### SYNOPSIS

> ``[PS] #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, [SS] or SCHED_SPORADIC, the result is implementation-defined; this case includes the SCHED_OTHER policy.

> [SS] 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

> XBD <sched.h>

#### CHANGE HISTORY

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

#### Issue 6

> The sched_setscheduler() 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:

> - In the DESCRIPTION, the effect of this function on a thread's scheduling parameters is added.

> - Sections describing two-level scheduling and atomicity of the function are added.

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

#### 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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