jackd on FreeBSD calls pthread_setschedparam(thread, SCHED_FIFO, &rtparam) with rtparam.sched_priority = 10. I am wondering where does 10 come from? The range for SCHED_FIFO is 0 .. 31, as returned by sched_get_priority_min() and sched_get_priority_max(). The value 10 seems wrong, since the fastest priority is 0, the slowest is 31. In controlapi.c sched_get_priority_min()/sched_get_priority_max() are called for OpenBSD. For this purpose FreeBSD should be the same. So it should be #ifndef __OpenBSD__ && defined(__FreeBSD__). Another problem is that FreeBSD doesn't allow to set thread priorities for non-root users, but jackd is supposed to run by the regular user. At least that's what libs expect it to be (/tmp/jack-{userid}). I have a suggestion: if the process is run with realtime priority, jackd shouldn't attempt to call pthread_setschedparam at all, because the process realtime priority should be sufficient. This code: struct rtprio rtp; res = rtprio(RTP_LOOKUP, getpid(), &rtp); if (rtp.type != RTP_PRIO_REALTIME) { // call pthread_setschedparam } allows to read priority of the process on FreeBSD. The process can be run with realtime priority with this command: rtprio 0 jackd ... Yuri