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_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() system calls conform to IEEE Std
     1003.1b-1993 (“POSIX.1”).