An FYI post for the archives.
From a local xterm on a Cygwin X server, I was able to open xterm windows to various remote hosts over ssh. However, on one fresh minimal installation of Debian Sarge
ssh -Yf <user>@<host> xterm (and other related commands) produced various errors: X11 connection rejected because of wrong authentication xterm Xt error: Can't open display: unable to open display I was able to open xterm's over ssh from other hosts. I installed xauth on the remote host: apt-get install xbase-clients I verified my configuration against the Cygwin/X FAQ: http://x.cygwin.com/docs/faq/cygwin-x-faq.html#q-ssh-no-x11forwarding In the local xterm DISPLAY was set to localhost:0 and was exported. On a different remote host where xterm worked properly, /etc/ssh/sshd_config had the following line: X11UseLocalhost no But on the remote host with non-working xterm, the command "xauth list" showed no fully-qualified host names apart from localdomain: debian/unix:10 MIT-MAGIC-COOKIE-1 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx localhost.localdomain:10 MIT-MAGIC-COOKIE-1 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx localhost.localdomain:11 MIT-MAGIC-COOKIE-1 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx debian/unix:11 MIT-MAGIC-COOKIE-1 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx So this needed to be in sshd_config: X11UseLocalhost yes (which is the default) after restarting the ssh daemon on the remote host: /etc/init.d/ssh restart My xterm window appeared. The rest of this post is the sshd_config for that host, verbatim. -- Poor Yorick ---*** begin /etc/ssh/sshd_config # Package generated configuration file # See the sshd(8) manpage for details # What ports, IPs and protocols we listen for Port 22 # Use these options to restrict which interfaces/protocols sshd will bind to #ListenAddress :: #ListenAddress 0.0.0.0 Protocol 2 # HostKeys for protocol version 2 HostKey /etc/ssh/ssh_host_rsa_key HostKey /etc/ssh/ssh_host_dsa_key #Privilege Separation is turned on for security UsePrivilegeSeparation yes # Lifetime and size of ephemeral version 1 server key KeyRegenerationInterval 3600 ServerKeyBits 768 # Logging SyslogFacility AUTH LogLevel INFO # Authentication: LoginGraceTime 600 PermitRootLogin yes StrictModes yes RSAAuthentication yes PubkeyAuthentication yes #AuthorizedKeysFile %h/.ssh/authorized_keys # Don't read the user's ~/.rhosts and ~/.shosts files IgnoreRhosts yes # For this to work you will also need host keys in /etc/ssh_known_hosts RhostsRSAAuthentication no # similar for protocol version 2 HostbasedAuthentication no # Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication #IgnoreUserKnownHosts yes # To enable empty passwords, change to yes (NOT RECOMMENDED) PermitEmptyPasswords no # Change to no to disable s/key passwords #ChallengeResponseAuthentication yes # Change to yes to enable tunnelled clear text passwords PasswordAuthentication no # To change Kerberos options #KerberosAuthentication no #KerberosOrLocalPasswd yes #AFSTokenPassing no #KerberosTicketCleanup no # Kerberos TGT Passing does only work with the AFS kaserver #KerberosTgtPassing yes #X11Forwarding no #(default) X11Forwarding yes #X11UseLocalhost yes (default - shown here for clarity) X11UseLocalhost yes X11DisplayOffset 10 PrintMotd no PrintLastLog yes KeepAlive yes #UseLogin no #MaxStartups 10:30:60 #Banner /etc/issue.net Subsystem sftp /usr/lib/sftp-server UsePAM yes -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://x.cygwin.com/docs/ FAQ: http://x.cygwin.com/docs/faq/