Error: Cannot Connect to display

In some virtual box images which does not have GUI support, the error mentioned in the title is encountered. This is because it does not support GUI and so it cannot display a graphical interface.

However, whether you are using Windows or Linux,there is a solution to this.

Step 1: Make sure you have host only networking adapter on your vm.

Make sure that you add an adapter with host only networking enabled on that adapter.
If you have host-only networking enabled, you will see an interface on your image with a class C ip address.
The IP Address is a class C address like 192.168.56.103.

To know this address use the commands ifconfig(if your image is linux based) or ipconfig(if your host is windows based.)

It will also have a class A address like 10.0.0.3 if you have NAT adapter enabled. This is used for connecting the virtualbox to the internet.

Step 2: Connecting to guest from host.

If you are accessing the guest using a command line, use the following command to access the guest and you do not need to follow step 3.

ssh -X username@address        ----------where -X enables X11 forwarding, username is the username  of the image and address is the host-only address of the guest.

If you are using a Windows host.

Make sure that you enable X11 forwarding in the ssh client(Eg, Putty, Secure Crt) you are using.

In Putty,Go to Connection > SSH > X11 > Check mark the X11 Forwarding option.
In Secure Crt, Go to Connection--> Port Forwarding--> Remote/X11 and check the Enforce X11 authentication checkbox

Step 3: Start Xming(If you are using Windows host)

Download Link : http://www.straightrunning.com/XmingNotes/

If you are using the Windows as a host you will need to start Xming first, which is a display server for Windows.

Now, to display the GUI for applications use the command xterm to open the GUI.
For eg.: In case of mininet use 'xterm s1' to display the xterm window for switch 1.