The fixed priority scheduling class (FX) assigns fixed priorities and time quantum that are not adjusted to accomodate resource consumption. Process priority can be changed only by the process itself or another appropriately privileged process. For more information about FX, see the priocntl(1) and dispadmin(1M) manual pages.
Threads in this class share the same range of priorities (0 to 59) as the TS and interactive (IA) scheduling classes. TS is usually the default. FX will usually be used in conjunction with TS.