sched_setparam(3)sched_setparam(3)NAMEsched_setparam - Sets the scheduling parameters of the specified
process (P1003.1b)
SYNOPSIS
#include <sched.h>
int sched_setparam ( pid_t pid, const struct sched_param *param);
LIBRARY
Realtime Library (librt.so, librt.a)
PARAMETERS
Specifies the ID of the process whose scheduling parameters are set. If
pid is zero, the scheduling parameters of the calling process are set.
Specifies a pointer to a sched_param structure, which contains the
scheduling parameters of the specified process. Currently, the
sched_param structure contains only a priority field. The value of the
priority value is any integer within the priority range for the current
scheduling policy of the process specified by pid.
DESCRIPTION
The sched_setparam function changes the scheduling parameters of a
process. Setting priorities such that the most critical process has the
highest priority allows applications to determine more effectively when
a process will run.
At run time, a process starts out with an initial priority of
SCHED_PRIO_USER_MAX. A call to the sched_setparam function that raises
the priority of a process also raises the maximum priority for the
process. This higher maximum priority exists for the life of the
process or until the priority is set to a new, higher priority through
another call to the sched_setparam function. The maximum priority can‐
not be adjusted downward, but subsequent calls to the sched_setparam or
sched_setscheduler functions can specify that a process run at a lower
priority.
You must have superuser privileges to set the priority above the user
maximum, SCHED_PRIO_USER_MAX. A superuser can set the priority outside
the range of the specified pid's scheduling policy.
When the function completes, the target process resumes execution after
all other runnable processes of equal or greater priority are scheduled
to run. If the priority of the target process is set higher than that
of the calling process, and if the target process is ready to run, then
the target process will preempt the calling process. If the calling
process set its own priority lower than some other process, then the
other process will preempt the calling process. In either situation,
the calling process might not receive notification of the completion of
the requested priority change until the target process has executed.
The scheduling parameters of the process as indicated by pid are
obtained with a call to the sched_getparam function.
The priority of a process is inherited across fork and exec calls.
RETURN VALUES
On a successful call to the sched_setparam function, the scheduling
parameters are set and a value of 0 (zero) is returned. On an unsuc‐
cessful call, a value of -1 is returned and errno is set to indicate
that an error occurred and the priority is unchanged.
ERRORS
The sched_setparam function fails under the following conditions: One
or more of the requested scheduling parameters is outside the range
defined for the specified pid's scheduling policy. This error does not
apply for superusers. The requesting process does not have permission
to set the scheduling parameters for the specified process, nor does it
have appropriate privilege to invoke the sched_setparam function. No
process can be found corresponding to that specified by pid.
SEE ALSO
Functions: getpid(2), sched_getparam(3), sched_getscheduler(3),
sched_setscheduler(3)
Guide to Realtime Programming
sched_setparam(3)
