Installing the Oracle Database - Expert Consolidation in Oracle Database 12c - page 179

Forwarding an X11 session
Most database administrators will use some variant of the Microsoft Windows operating system on their workstations
or desktops. For them to use X11 forwarding, they need to install an X server which has to be started up and accepting
connections on their workstations. Free/Open Source X Servers include the Cygwin environment for example. In
addition to the Open Source X Servers, commercial products are available as well. It is more a matter of personal taste
as to which one to choose. To allow X11 forwarding on the database server you need to modify the SSH server daemon
configuration file on the database server.

■ Note Check with your security department if X11-forwarding is allowed in your environment before enabling it.

For an OpenSSH implementation, you need to add/modify the following variable in /etc/ssh/sshd_config and
reload the configuration. The below example is for Linux, after the variable X11Forwarding has been uncommented
out and set to yes:

[root@server1 ~] # grep X11Forwarding /etc/ssh/sshd_config
X11Forwarding yes
[root@server1 ~] # service sshd reload
Reloading sshd: [ OK ]
[root@server1 ~] #

In your putty configuration, ensure to enable X11 forwarding. For putty's new connection dialog, navigate to
Connection ➤ SSH ➤ X11, tick the checkbox named “Enable X11 Forwarding” before connecting to the server. Unlike
port forwarding you can't retrospectively enable X11 forwarding. Your next session will show lines similar to these:

login as: grid
[e-mail]'s password:
Last login: Fri Sep 6 15:31:29 2013 from jumpbox
/usr/bin/xauth: creating new authority file /home/grid/.Xauthority
$ echo $DISPLAY
localhost:10.0

You can use the xdpyinfo application to check if your terminal session can connect to the X server, which should
be the case. This little utility displays information about the X server. Any output different from the below example
indicates you can successfully forward your X11 session:

xdpyinfo: unable to open display "".

Using the Virtual Network Computing Protocol
An alternative to X-forwarding exists in the form of VNC. It is easiest to picture VNC as an operating system
independent equivalent to the Microsoft Terminal Services client. VNC is based on a client/server architecture, and
supports many operating systems. It is very common to start a server session on Linux and use a Windows client.
The VNC server is slightly easier to configure than X11 forwarding. It does not require a change to the SSH daemon
configuration which can be difficult to arrange.