int sched_get_priority_max(int policy);
sched_get_priority_max returns the maximum priority value that can be used with the scheduling algorithm identified by policy. sched_get_priority_min returns the minimum priority value that can be used with the scheduling algorithm identified by policy. Supported policy values are SCHED_FIFO, SCHED_RR, and SCHED_OTHER.
Processes with numerically higher priority values are scheduled before processes with numerically lower priority values. Thus, the value returned by sched_get_priority_max will be greater than the value returned by sched_get_priority_min.
Linux allows the static priority value range 1 to 99 for SCHED_FIFO and SCHED_RR and the priority 0 for SCHED_OTHER. Scheduling priority ranges for the various policies are not alterable.
The range of scheduling priorities may vary on other POSIX systems, thus it is a good idea for portable applications to use a virtual priority range and map it to the interval given by sched_get_priority_max and sched_get_priority_min. POSIX.1b requires a spread of at least 32 between the maximum and the minimum values for SCHED_FIFO and SCHED_RR.
sched_setscheduler(2) has a description of the Linux scheduling scheme.