Virtual Network Computing (VNC) is a graphical dekstop sharing system. Usign remote framebuffer or RFC protocol it can enable the controls over the remote computers.

On Linux Servers if VNC server is installed and configured,you can access it using graphical X windows display same as Remote Desktop appplication built on newer versions of Microsoft Windows.
A VNC consists of a client, a server, and a communication protocol

* The VNC server shares its screen. The server passively allows the client to take control of it.
* The VNC client (or viewer) is the program that watches, controls, and interacts with the server. The client controls the server.
* The VNC protocol is based on remote framebuffer (RFB) protocol.

A VNC viewer may connect to a VNC server on the same or any other operating system. Multiple clients may connect to a VNC server at the same time.
If you are having CentOS server and wish to connect to graphically using X windows you can follow these steps

Check if the VNC server is already installed or not

rpm -qa vnc-server

If you get an output as “package vnc-server is not installed” you can begin with the installation.
Install VNC server with the following Command

yum install vnc-server

Now check if VNC client is installed on the server use the command

rpm -qa vnc

Install it if needed by using the following command

yum install vnc

Now lets install the Gnome Desktop and requirements by executing the command

IF you are using CentOS 5 ::-

yum groupinstall “GNOME Desktop Environment”

IF you are using CentOS 6 ::-

yum groupinstall Desktop

On CentOS 5 you may get error regarding “libgaim.so.0” if so, you may use below steps to overcome by using

yum –exclude=nautilus-sendto groupinstall “GNOME Desktop Environment”

Now lets create user to access the server

useradd test

To allow its access by configuring the configuration file /etc/sysconfig/vncservers with the following parameters

VNCSERVERS=”5:test”
VNCSERVERARGS[1]=”-geometry 800×600″

Now lets set password for the user

su – test

vncpasswd

If you wish to use root user to be accessed using VNC use following setting in /etc/sysconfig/vncservers

VNCSERVERS=”5:root”
VNCSERVERARGS[1]=”-geometry 800×600″

As root execute
vncpasswd


Check  the port on which the service is functioning with the command

ps -faux  | grep vnc

To start VNC server issue command

vncserver -kill :5

To start VNC server issue command

vncserver :5

Now you can access the server graphically as illustrated below

You will get a prompt as

On connecting you will get message as below