int sched_setparam (
const struct sched_param *param);
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 runtime, 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 cannot 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.
The target process, whether it is running or not, 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 sets 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.
On a successful call to the sched_setparam function, the scheduling parameters are set and a value of 0 is returned. On an unsuccessful call, a value of -1 is returned and errno is set to indicate that an error occurred and the priority is unchanged.
The sched_setparam function fails under the following conditions:
Functions: getpid(2), sched_getparam(3), sched_getscheduler(3), sched_setscheduler(3) delim off