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NAME

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

LIBRARY

     Standard C Library (libc, -lc)

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() system call 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 system call
     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 IEEE Std
     1003.1b-1993 (“POSIX.1”) 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() system call 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 IEEE Std
     1003.1b-1993 (“POSIX.1”) 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 system call
     will fail if pid is negative.

RETURN VALUES

     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set 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 IEEE Std 1003.1b-1993 (“POSIX.1”).

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

     [EINVAL]           The value of the policy argument 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_getparam(2), sched_get_priority_max(2), sched_get_priority_min(2),
     sched_rr_get_interval(2), sched_setparam(2), sched_yield(2)

STANDARDS

     The sched_setscheduler() and sched_getscheduler() system calls conform to
     IEEE Std 1003.1b-1993 (“POSIX.1”).