What I want to achieve: Open an ssh connection (from Ubuntu client) to ssh daemon on opensuse 12.2 with X11 forwarding. Command line is
ssh -X host
It fails with sshd: error: Failed to allocate internet-domain X11 display socket. in /var/log/messages.
Solution was the entry
in host’s /etc/ssh/sshd_config (don’t forget to restart service)