VNC (Virtual Network Computing ) is a graphical desktop sharing system that uses the Remote Frame Buffer protocol to remotely control another coumputer on a network.
To run the VNC Server on CentOS, we have to install these required packages:
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yum groupinstall Desktop
yum install tigervnc-server
yum install xorg-x11-fonts-Type1
yum install vnc

To start VNC Server on boot

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chkconfig vncserver on
 useradd arbab 

To setup users’ VNC password:

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su - arbab
vncpasswd

Edit the /etc/sysconfig/vncservers file:

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nano /etc/sysconfig/vncservers

Add the following to the end of the file:

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VNCSERVERS="1:arbab"
VNCSERVERARGS[1]="-geometry 1024x600"

The iptables rules need to be amended to open the VNC ports:

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iptables -I INPUT 5 -m state --state NEW -m tcp -p tcp -m multiport --dports 5901:5903,6001:6003 -j ACCEPT
service iptables save
service iptables restart
Restart the VNC Server:
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service vncserver restart

Now kill the VNC Server:

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vncserver -kill :1

Edit the xstartup file in .vnc directory:

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nano .vnc/xstartup
Comment the last line and run the Gnome:
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#twm & 
exec gnome-session &

Restart the service:

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service vncserver restart

Now, download VNCViewer onto our desktop computer from which we want to access the shared desktop.
Connect using ServerIP/Name:1 (:1 is for the VNC server window)

http://www.realvnc.com/download/viewer/

Enter the password that we created using the vncpasswd command:

Ability to connect for multiple users:
Create a local user, using the following command:

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adduser ali

Create a password for newly created user:

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passwd ali

Switch to the newly created user and run vncpasswd command for it:

su ali

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vncpasswd

Edit the /etc/sysconfig/vncservers file:

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nano /etc/sysconfig/vncservers

Add these lines for new user:

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VNCSERVERS="1:arbab 2:ali"
VNCSERVERARGS[1]="-geometry 1024x600"
VNCSERVERARGS[2]="-geometry 1024x600"

Restart the VNC service:

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service vncserver restart

Kill the vncserver session for new user and edit the xstartup file:

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su ali
vncserver -kill :2
cd ~
nano .vnc/xstartup
Modify the file so it looks like this:
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#twm & 
exec gnome-session &
Restart the VNC service:
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service vncserver restart

Connect with newly created user using centos:2, Where centos is my server name:

Enter the password that we created using the vncpasswd command: