If the database is not initialized then other programs will complain.
Reported-by: Jeongkeun Lee <jklee@hp.com>
% ovsdb-server /etc/ovs-vswitchd.conf.db --remote=punix:/var/run/ovsdb-server
+Then initialize the database with "ovs-vsctl init". This is only
+necessary the first time after you create the database with
+ovsdb-tool (but running it at any time is harmless):
+
+ % ovs-vsctl init
+
Then start the main Open vSwitch daemon, telling it to connect to the
same Unix domain socket: