SCHED_SETSCHEDULER(2)

NAME
sched_setscheduler, sched_getscheduler - set/get scheduling policy and scheduler parameters

LIBRARY
libc

SYNOPSIS
#include <sched.h>
int
sched_setscheduler(pid_t pid, int policy, const struct sched_param *param);
int
sched_getscheduler(pid_t pid);

DESCRIPTION
The sched_setscheduler() function sets 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 param structure must be any integer within the inclusive priority range for the scheduling policy specified by policy.

In this implementation, if the value of pid is negative the function will fail.

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

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

In this implementation, the policy of when a process can affect the scheduling parameters of another process is specified in p1003_1b as a write-style operation.

The scheduling policies are in <sched.h>:

[SCHED_FIFO]
    First-in-first-out fixed priority scheduling with no round robin scheduling;

[SCHED_OTHER]
    The standard time sharing scheduler;

[SCHED_RR]
    Round-robin scheduling across same priority processes.

The sched_param structure is defined in <sched.h>:

    struct sched_param {
    	int sched_priority;	/* scheduling priority */
    };

The sched_getscheduler() function returns the scheduling policy of the process specified by pid.

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

In this implementation, the policy of when a process can obtain the scheduling parameters of another process are detailed in p1003_1b as a read-style operation.

If pid is zero, the scheduling parameters for the calling process will be returned. In this implementation, the sched_getscheduler function will fail if pid is negative.

RETURN
The function will return zero if it completes successfully, or it will return a value of -1 and set errno to indicate the error.

ERRORS
On failure errno will be set to the corresponding value:

[ENOSYS]
    The system is not configured to support this functionality.

[EPERM]
    The requesting process doesn not have permission as detailed in p1003_1b.

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

[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.

SEE ALSO
sched_get_priority_max(2), sched_get_priority_min(2), sched_getparam(2), sched_rr_get_interval(2), sched_setparam(2), sched_yield(2)

STANDARDS
The sched_setscheduler() and sched_getscheduler() functions conform to p1003.1b-93.