start: only preserve CLONE_NEWCGROUP when supported

src/lxc/start.c

@@ -1402,6 +1402,7 @@ static int lxc_spawn(struct lxc_handler *handler)
 	if (lxc_sync_barrier_child(handler, LXC_SYNC_READY_START))
 		return -1;
 
+	if (cgns_supported()) {
 		ret = lxc_preserve_ns(handler->pid, "cgroup");
 		if (ret < 0) {
 			ERROR("%s - Failed to preserve cgroup namespace", strerror(errno));
@@ -1409,6 +1410,7 @@ static int lxc_spawn(struct lxc_handler *handler)
 		}
 		handler->nsfd[LXC_NS_CGROUP] = ret;
 		DEBUG("Preserved cgroup namespace via fd %d", ret);
+	}
 
 	if (lxc_network_recv_name_and_ifindex_from_child(handler) < 0) {
 		ERROR("Failed to receive names and ifindices for network "