We've been using libvirt based containers under CentOS 7 and everything has been working fine. One application we run in our containers is ctdb, which uses SCHED_FIFO (real time) threads. This has been working without problems until our recent upgrade to CentOS 7.3. For some reason, ctdb is no longer able to create real time threads, and I've tried a simple program myself that confirms this. The same program works fine on the hypervisor so I know the kernel supports real time. Does anyone know what may have changed in CentOS 7.3 that breaks real time threads in libvirt containers? This is the simple test program I created to verify the real time threads are failing. This same program works in a libvirt container in CentOS 7.2. #include <stdio.h> #include <string.h> #include <pthread.h> pthread_t test_thread; void *test(void *arg) { printf("Starting thread\n"); sleep(1); printf("Thread complete\n"); return 0; } int main(int argc, char *argv[]) { int rc; printf("Starting main\n"); struct sched_param tsparam; pthread_attr_t tattr; memset(&tsparam, 0, sizeof(tsparam)); pthread_attr_init(&tattr); pthread_attr_setinheritsched(&tattr, PTHREAD_EXPLICIT_SCHED); pthread_attr_setschedpolicy(&tattr, SCHED_FIFO); tsparam.sched_priority = sched_get_priority_max(SCHED_FIFO) - 7; pthread_attr_setschedparam(&tattr, &tsparam); if ((rc = pthread_create(&test_thread, &tattr, test, NULL)) != 0) { printf("Unable to start rt thread\n"); } return 0; }