Mayur's BLOG

VNC ( Virtual Network Computing ) is used to display an X windows session running on another computer. Unlike a remote X connection, the xserver is running on the remote computer, not on your local workstation. Your workstation ( Linux or Windows ) is only displaying a copy of the display ( real or virtual ) that is running on the remote machine.

There are several ways to configure the vnc server. This HOWTO shows you how to configure VNC using the 'vncserver' service as supplied by CentOS.

1. Installing the required packages

The server package is called 'vnc-server'. Run the command rpm -q vnc-server.

The result will be either package vnc-server is not installed or something like vnc-server-4.0-11.el4.

If the server is not installed, install it with the command: yum install vnc-server.

The client program is 'vnc'. You can use the command yum install vnc to install the client if rpm -q vnc shows that it is not already installed.

Make sure to install a window manager in order to get a normal GUI desktop. You can use the command yum groupinstall "GNOME Desktop Environment" to install the Gnome Desktop and requirements, for example. Other popular desktop environments are "KDE" and "XFCE-4.4". XFCE is more light-weight than Gnome or KDE and available from the "extras" repository.

For my installation I used XFCE :: yum install XFCE

2. Configuring un-encrypted VNC
We will be setting up VNC for 3 users. These will be 'larry', 'moe', and 'curly'.

You will perform the following steps to configure your VNC server:

1. Create your VNC users.
2. Set your users' VNC passwords.
3. Edit the server configuration.
4. Create and customize xstartup scripts.
5. Start the VNC service.
6. Test each VNC user.
7. Setup the VNC service to start on reboot.
8. Additional optional enhancements

2.1. Create your VNC users

As root:
$ su -
# useradd larry
# useradd moe
# useradd curly
# passwd larry
# passwd moe
# passwd curly

2.2. Set your users' VNC passwords
Login to each user, and run vncpasswd. This will create a .vnc directory.
[~]$ cd .vnc
[.vnc]$ ls
passwd

2.3. Edit the server configuration
Edit /etc/sysconfig/vncservers, and add the following to the end of the file.

VNCSERVERS="1:larry 2:moe 3:curly"
VNCSERVERARGS[1]="-geometry 640x480"
VNCSERVERARGS[2]="-geometry 640x480"
VNCSERVERARGS[3]="-geometry 800x600"

Larry will have a 640 by 480 screen, as will Moe. Curly will have an 800 by 600 screen.

2.4. Create xstartup scripts

We will create the xstartup scripts by starting and stopping the vncserver as root.

# /sbin/service vncserver start
# /sbin/service vncserver stop

Login to each user and edit the xstartup script. To use Larry as an example, first login as larry

[~]$ cd .vnc
[.vnc] ls
mymachine.localnet:1.log passwd xstartup

Edit xstartup. The original should look like:

#!/bin/sh
# Uncomment the following two lines for normal desktop:
# unset SESSION_MANAGER
# exec /etc/X11/xinit/xinitrc
[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid grey
vncconfig -iconic &
xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
twm &

Add the line indicated below to assure that an xterm is always present, and uncomment the two lines as directed if you wish to run the user's normal desktop window manager in the VNC. Note that in the likely reduced resolution and color depth of a VNC window the full desktop will be rather cramped and a look bit odd. If you do not uncomment the two lines you will get a gray speckled background to the VNC window.


#!/bin/sh
# Add the following line to ensure you always have an xterm available.
( while true ; do xterm ; done ) &
# Uncomment the following two lines for normal desktop:
unset SESSION_MANAGER
exec /etc/X11/xinit/xinitrc
[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid grey
vncconfig -iconic &
xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
twm &

2.5. Start the VNC server

Start the vncserver as root

# /sbin/service vncserver start

2.6. Test each VNC user

Let us assume that mymachine has an IP address of 192.168.0.10. The URL to connect to each of the users will be:

Larry is http://192.168.0.10:5801
Moe is http://192.168.0.10:5802
Curly is http://192.168.0.10:5803

Connect to http://192.168.0.10:5801. A java applet window will pop-up showing a connection to your machine at port 1. Click the [ok] button. Enter larry's VNC password, and a 640x480 window should open using the default window manager selected for larry . The above ports 5801, 5802 and 5803 must be open in the firewall {iptables) for the source IP addresses or subnets of a given client.

2.6.2. Testing with a vnc client
For Larry: vncviewer 192.168.0.10:1
For Moe: vncviewer 192.168.0.10:2
For Curly: vncviewer 192.168.0.10:3

To test larry using vncviewer, vncviewer 192.168.0.10:1. Enter Larry's VNC password, and a 640x480 window should open using Larry's default window manager. The vncviewer client will connect to port 590X where X is an offset of 1,2,3 for Larry, Moe, and Curly respectively, so these ports must be open in the firewall for the IP addresses or subnets of the clients.

2.6.3. Starting vncserver at boot

To start vncserver at boot, enter the command /sbin/chkconfig vncserver on

That's it.

Regards,
Mayur C.
mayur.c24@gmail.com