View source for Running and Connecting to VNC Servers on a Xen Guest (domainU) System

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<td width="20%">[[Configuring a VNC based Graphical Console for a Xen Paravirtualized domainU Guest|Previous]]<td align="center">[[Xen Virtualization Essentials|Table of Contents]]<td width="20%" align="right">[[Adding Disk, CDROM and DVD Devices to a Running Xen domainU Guest System|Next]]</td>
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<td width="20%">Configuring a VNC based Graphical Console for a Xen Paravirtualized domainU Guest<td align="center"><td width="20%" align="right">Adding Disk, CDROM and DVD Devices to a Running Xen domainU Guest System</td>
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<google>BUY_XEN_ESSENTIALS</google>


In the previous chapter we looked at enabling VNC support in domain0 for the purpose of providing a remote graphical display for a Xen domainU guest. This approach works well in situations where only one graphical desktop is required. In situations where multiple graphical desktops are required (for example, it is quite likely that more than one user will want to be logged into a desktop at any one time) it is necessary to run instances of the VNC server on the domainU guest rather than rely on the VNC support provided by domain0. The purpose of this chapter is to describe in detail how to achieve such a configuration.

== Installing VNC on the Xen domainU Guest ==

The very first step in the configuration process involves ensuring that VNC support is installed on the domainU guest. As domainU systems often use a minimal configuration it is possible that VNC has yet to be installed. The precise steps to install VNC vary between distributions. Check the documentation for your chosen distribution if you are unsure. A few examples are:

For Red Hat Linux, CentOS and Fedora:

<pre>
su -c 'yum install vnc'
</pre>

For Ubuntu Linux:

<pre>
sudo apt-get install vnc4server
</pre>

== Creating Xen domainU VNC Desktop Sessions ==

With VNC installed on the domainU guest system the next step involves the creation of ''VNC server'' sessions. There will need to be one VNC server session running for each independent desktop environment.

New desktop environments are created using the ''vncserver'' utility and each desktop is assigned a unique port number which is specified on the command-line. For example to launch desktop '':1'' run the following command from a terminal window command-line prompt:

<pre>
vncserver :1
</pre>

The ''vncserver'' tool will prompt for a password which will be required each time a remote user attempts to connect to the desktop. At this prompt enter a suitable password to protect access to the desktop.  Once a suitable password has been provided vncserver will start a new desktop in the background connected to port 5901 ready for a remote user to connect to using ''vncviewer''. The following transcript shows the typical output from an initial launch of a vncserver session:

<pre>
-bash-3.1$ vncserver :1

You will require a password to access your desktops.

Password:
Verify:

New 'localhost.localdomain:1 (nas)' desktop is localhost.localdomain:1

Creating default startup script /home/neil/.vnc/xstartup
Starting applications specified in /home/neil/.vnc/xstartup
Log file is /home/neil/.vnc/localhost.localdomain:1.log
</pre>

Note that since the above output is from the first time a vncserver session has been run by a particular user a number of default files have been created in the user's home directory. Of particular interest is the .vnc/xstartup file which will be modified later in this chapter to control the type of desktop environment to be invoked by VNC.

== Connecting to a Xen domainU Remote Desktop ==

There are two ways to connect to a VNC server session, securely and insecurely. The insecure method is not recommended unless the connection between the client and the server systems takes place within a secure network over a secure encrypted connection (such as a VPN). If the connection is taking place over the internet with no encryption then the secure method of connection is ''strongly'' recommended.

To establish an insecure connection simply run the ''vncviewer'' command on the client system specifying the IP address or host name of the  domainU system on which the VNC server session is running together with the VNC session port number (keeping in mind that VNC display :1 maps to port 5901, :2 to 5902 and so on). For example, if the domainU guest system has an IP address of 192.168.2.24 and we wish to connect to VNC display '':1'' we would need to execute the following command:

<pre>
vncviewer 192.168.2.24:5901
</pre>

To establish a secure connection we need to use SSH tunneling to establish an encrypted connection. This is achieved by first establishing the tunnel using the ''ssh'' command. In doing so we will map port 5901 on our local system to port 5901 on the remote domainU system (assuming that the VNC session is configured on display :1). This connection would be established as follows:

<pre>
ssh -l nas -L 5901:localhost:5901 192.168.2.24
</pre>

This time, when running ''vncviewer'' we now specify ''localhost'' instead of the remote system (since port 5901 on localhost is now mapped through the secure tunnel to port 5901 on the remote system):

<pre>
vncviewer 192.168.2.24:5901
</pre>

== Configuring the Xen domainU Desktop Environment ==

When the desktop appears you will notice that it doesn't look much like the standard desktop you would expect to see on most modern Linux distributions. In fact it may look something like the following figure:


[[Image:xen_domainU_remote_desktop_twm.jpg|A basic Xen domainU desktop running twm]]


The problem here is that by default VNC starts a minimal desktop environment (typically using a basic window manager known as ''twm'') so we need to configure the VNC session to launch the correct desktop. To do this exit from vncviewer and then shutdown the VNC desktop session on the domainU system as follows:

<pre>
vncserver -kill :1
</pre>

Next go to your home folder and edit the .vnc/xstartup file. This will look similar to the following file:

<pre>
#!/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 &
</pre>

To configure this startup script to launch, for example, the GNOME desktop environment change the ''twm&'' line so that the file reads:

<pre>
#!/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" &

unset SESSION_MANAGER
gnome-session &
</pre>

Restart the vncserver:

<pre>
vncserver :1
</pre>

Finally, reconnect from the remote system. The full desktop should now appear in the VNC viewer window:


[[Image:xen_vnc_domainU_gnome_desktop.jpg|The GNOME desktop running on a Xen domainU system displaying over VNC]]


If KDE is your preferred desktop simply change the xstartup file so that it executes ''startkde'' instead of ''twm'' or ''gnome-session''.

== Closing Down a domainU VNC Desktop Session ==

As long as the vncserver session is running the desktop will continue to run regardless of whether a ''vncviewer'' instance is connected. This means that you can exit from ''vncviewer'' and reconnect later and find your desktop exactly as you left it.

Before closing down the actual VNC server session it is important to verify that any applications running on the desktop in question have been cleanly exited to avoid loss of data. Once all applications are closed, log out of the desktop environment in the ''vncviewer'' session and then exit ''vncviewer''.

On the domainU guest system on which the ''vncserver'' server is running execute the ''vncserver'' command with the ''--kill'' option specifying the display to shut down. For example:

<pre>
vncserver -kill :1
</pre>

This will close down the VNC server session on display :1


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<hr>
<table border="0" cellspacing="0" width="100%">
<tr>
<td width="20%">[[Configuring a VNC based Graphical Console for a Xen Paravirtualized domainU Guest|Previous]]<td align="center">[[Xen Virtualization Essentials|Table of Contents]]<td width="20%" align="right">[[Adding Disk, CDROM and DVD Devices to a Running Xen domainU Guest System|Next]]</td>
<tr>
<td width="20%">Configuring a VNC based Graphical Console for a Xen Paravirtualized domainU Guest<td align="center"><td width="20%" align="right">Adding Disk, CDROM and DVD Devices to a Running Xen domainU Guest System</td>
</table>