Comment puis-je ouvrir et afficher graphiquement un fichier du côté client sous Linux via une connexion SSH ?

Vous devez utiliser le -X avec l'option ssh :

 -X      Enables X11 forwarding.  This can also be specified on a per-host
         basis in a configuration file.

         X11 forwarding should be enabled with caution.  Users with the
         ability to bypass file permissions on the remote host (for the
         user's X authorization database) can access the local X11 display
         through the forwarded connection.  An attacker may then be able
         to perform activities such as keystroke monitoring.

         For this reason, X11 forwarding is subjected to X11 SECURITY
         extension restrictions by default.  Please refer to the ssh -Y
         option and the ForwardX11Trusted directive in ssh_config(5) for
         more information.

Le serveur doit également prendre en charge le transfert de X en /etc/ssh/sshd_config :

 X11Forwarding
         Specifies whether X11 forwarding is permitted.  The argument must
         be “yes” or “no”.  The default is “no”.

         When X11 forwarding is enabled, there may be additional exposure
         to the server and to client displays if the sshd(8) proxy display
         is configured to listen on the wildcard address (see
         X11UseLocalhost below), though this is not the default.
         Additionally, the authentication spoofing and authentication data
         verification and substitution occur on the client side.  The
         security risk of using X11 forwarding is that the client's X11
         display server may be exposed to attack when the SSH client
         requests forwarding (see the warnings for ForwardX11 in
         ssh_config(5)).  A system administrator may have a stance in
         which they want to protect clients that may expose themselves to
         attack by unwittingly requesting X11 forwarding, which can
         warrant a “no” setting.

         Note that disabling X11 forwarding does not prevent users from
         forwarding X11 traffic, as users can always install their own
         forwarders.  X11 forwarding is automatically disabled if UseLogin
         is enabled.

Alors vous pouvez l'utiliser :

$ ssh -X user@host xclock

Ajoutez simplement "-X" (X11 forwarding) à votre ligne de commande ssh. Cela activera la redirection X11 et configurera la variable DISPLAY, etc. et vous devriez être en mesure de faire ce que vous demandez.