Samba start / restart error: smbd_open_once_socket: open_socket_in: Addr

Once I have got this problem with samba in Oracle Linux 6 (the same I could reproduce in RedHat 6 as well):

On start or restart of smb service var/log/samba/log.smbd reports:

smbd/server.c:501(smbd_open_one_socket) smbd_open_once_socket: open_socket_in: Address already in use

The solution was:

sysctl net.ipv6.bindv6only=1

as it looks like the problem happens on systems which IPv6 support where :: also listens for IPv4 connections. So the bind to 0.0.0.0 fails.