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VNX Simple Scenarios


Several simple example scenarios are included in VNX distribution to allow testing the tool functionalities with the different types of virtual machines supported (see /usr/share/vnx/examples/simple_*.xml files).

Each simple scenario includes just one virtual machine connected to a virtual network (Net0,, where the hosts has also a virtual network interface connected (

The simple scenarios are prepared to be started and tested individually or to be started all together to form the compound scenario shown in Figure 1.

Figure 1: simple scenarios topology

The following simple scenarios are available:

Scenario file name Description VM ip address
simple_uml.xml Just one User Mode Linux (UML) Debian system
simple_winxp.xml Just one KVM Windows XP system
simple_ubuntu.xml Just one KVM Ubuntu system without GUI
simple_ubuntu-gui.xml Just one KVM Ubuntu system with minimal GNOME GUI
simple_freebsd.xml Just one KVM FreeBSD system without GUI
simple_freebsd-gui.xml Just one KVM FreeBSD system with minimal GNOME GUI
simple_win7.xml Just one KVM Windows 7 system
simple_fedora.xml Just one KVM Fedora system without GUI
simple_fedora-gui.xml Just one KVM Fedora system with a GNOME GUI
simple_dynamips.xml Just one Dynamips emulated CISCO 3600 router
simple_dynamips2.xml Just one Dynamips emulated CISCO 7200 router
simple_olive.xml Just one Olive emulated Juniper router
simple_centos.xml Just one KVM CentOS system without GUI
simple_centos-gui.xml Just one KVM CentOS system with a GNOME GUI

All scenarios are available in /usr/share/vnx/examples directory. See, for example, the content of simple_ubuntu-gui.xml scenario at the end of this page

Starting a simple scenario

You can start VNX scenarios either from a local shell window or remotely using an SSH session with X-forwarding enabled. For example, if you connect to the VNX host from a Unix or MacOS system you can use:

  ssh -X <vnx-host-address-or-name>

If you connect from another system, just investigate how to configure your SSH client to do X-forwarding (most of them include it).

In case of remote connections, it is recommended to test that X-forwarding is working by launching a "xterm" or "xeyes" application and checking that the application window is correctly launched. Beware that X-forwarding is very bandwidth consuming, so you will need a good connectivity between your system and the host were VNX runs.

As VNX needs root priviledges, you have to be root in the shell window or, alternatively, if your account is allowed to "sudo" root (as typically is, for example, in Ubuntu systems), just precede vnx commands with "sudo", as shown below.

To start, for example, the simple_ubuntu-gui scenario:

cd /usr/share/vnx/examples/
sudo vnx -f simple_ubuntu-gui.xml -v --create

You will see the two virtual machine consoles opening: the graphical one showing the gnome desktop and the text console.

Figure 2: Graphical and textual consoles of simple_ubuntu-gui scenario

Beware that, once the virtual machine has completely started, the VNX autoconfiguration daemon (VNXACED) has to do its job configuring the name and the network interfaces parameters and restarting the machine for the changes to take effect. After that restart, the virtual machine is ready to be used.

Once started, you can test the network connectivity from the host to the virtual machine:

# ping -c 4
PING ( 56(84) bytes of data.
64 bytes from icmp_seq=1 ttl=64 time=0.197 ms
64 bytes from icmp_seq=2 ttl=64 time=0.188 ms
64 bytes from icmp_seq=3 ttl=64 time=0.177 ms
64 bytes from icmp_seq=4 ttl=64 time=0.171 ms

--- ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3001ms
rtt min/avg/max/mdev = 0.171/0.183/0.197/0.013 ms

If you close the consoles, you can reopen them with the following commands:

sudo vnx -f simple_ubuntu-gui.xml -v --console con0 -M ubuntu-gui
sudo vnx -f simple_ubuntu-gui.xml -v --console con1 -M ubuntu-gui

Or much simpler, you can use libvirt commands:

# sudo virsh list
 Id Nombre               Estado
 31 ubuntu-gui           running
# virt-viewer 31 &                       # To open the graphical console
# xterm -e "sudo virsh console 31" &     # To open the text console

Beware that only one textual console can be used at a time. If you open a second one, you will experiment a strange behaviour as both consoles will compete for the pts terminal. On the contrary, you can open several graphical console simultaneously.

See VNX Console Management for more details.

Executing commands

You can also execute commands on the virtual machine from the host by means of the <exec> tags in the XML scenario specification:

For example, you can start the calculator or the xeyes application on the virtual machine by issuing:

sudo vnx -f simple_ubuntu-gui.xml -v --exe calc
sudo vnx -f simple_ubuntu-gui.xml -v --exe xeyes

Those commands execute what is defined in the <exec> tags with seq="calc" or seq="xeyes" respectively:

<!-- Start xeyes application -->
<exec seq="xeyes"    type="verbatim" ostype="xexec">xeyes</exec>

<!-- Start calculator  -->
<exec seq="calc"      type="verbatim" ostype="xexec">gcalctool</exec>
<exec seq="calcoff"   type="verbatim" ostype="system">pkill gcalctool</exec>

The "ostype" attribute is used to specify the type of command included in <exec> tag, either command line (CLI) or graphical (GUI), and whether vnx tool waits for command execution end or not. For values are posible:

ostype Type of commands Waits for command execution end
system CLI YES
exec CLI NO
xsystem GUI YES
xexec GUI NO

You can check, for example, the "xexec" value with:

sudo vnx -f simple_ubuntu-gui.xml -v --exe xeyes2

which executes the command:

<exec seq="xeyes2"    type="verbatim" ostype="xexec">xeyes</exec>

You will see the application xeyes opened in the virtual machine, but the command executed in the host will not end till the application is closed.

Or you can use a "system" command that closes (kills) all calc applications opened:

sudo vnx -f simple_ubuntu-gui.xml -v --exe calcoff

You can start or stop a web server in the virtual machine with:

sudo vnx -f /usr/share/vnx/examples/simple_ubuntu.xml -v --exe start-www
sudo vnx -f /usr/share/vnx/examples/simple_ubuntu.xml -v --exe stop-www

And test that the web server is running by manually opening a web navigator in the host and loading URL Alternativey, you can check the server availability with "nmap" tool:

# nmap -p 80

Starting Nmap 5.00 ( ) at 2011-07-28 00:48 CEST
Interesting ports on
80/tcp open  http
MAC Address: 02:FD:00:05:01:01 (Unknown)

Nmap done: 1 IP address (1 host up) scanned in 0.40 seconds

Apart from the <exec> tags which define the commands used to start the web server ("service apache2 start"), the command sequence "start-www" includes a <filetree> tag to copy files from the host to the virtual machine that it is used to copy the initial web page shown by the server.

 <!-- Copy the content of conf/txtfile directory in the host to
      the /var/www directory in the virtual machine -->
 <filetree seq="start-www" root="/var/www">conf/txtfile</filetree>
 <!-- Start/stop apache www server -->
 <exec seq="start-www" type="verbatim" ostype="system">service apache2 start</exec>
 <exec seq="stop-www"  type="verbatim" ostype="system">service apache2 stop</exec>

You can find more example commands by having a look at <exec> and <filetree> tags in simple_ubuntu-gui.xml file or in other simple_*.xml examples. And more information about command execution in here.

Stopping the scenario

To stop the scenario preserving the changes made inside virtual machines you have to use the "-d" or "--shutdown" option:

sudo vnx -f simple_ubuntu-gui.xml -v --shutdown

You can later restart the scenario with:

sudo vnx -f simple_ubuntu-gui.xml -v --create

To stop the scenario discarding all the changes made in the virtual machine use the "-P" or "--destroy" option:

sudo vnx -f simple_ubuntu-gui.xml -v --destroy

Tipically, virtual machines in VNX are created using "Copy-on-write (COW)" filesystems to allow sharing a root filesystem among several virtual machines.

In the definition of the virtual machine:

<filesystem type="cow">/usr/share/vnx/filesystems/rootfs_ubuntu-gui</filesystem>

you specify the root filesystem to use (/usr/share/vnx/filesystems/rootfs_ubuntu-gui) and how it is mounted (cow). Using COW mode, the virtual machine will use the root filesystem in read-only mode and use another filesystem to save the files modified. When you use "-P|--destroy" option to stop an scenario, vnx deletes the filesystem with the modifications.

Other interesting options

You can see a graphical map of the virtual scenario using the --show-map option:

 sudo vnx -f simple_ubuntu-gui.xml -v --show-map
Figure 3: simple_ubuntu-gui scenario topology

simple_ubuntu-gui.xml scenario

<?xml version="1.0" encoding="UTF-8"?>

VNX Sample scenarios

Name:        simple_ubuntu-gui
Description: Just one Ubuntu virtual machine with GUI connected to a Network named Net0 with address 
             The host has an interface in Net0 with address  
             This simple scenario is supposed to be used for testing the different 
             types of virtual machines supported by VNX. You can start several simple_*.xml
             scenarios and test the connectivity among virtual machines and the host, as all
             scenarios share the same "Net0" network.  

This file is part of the Virtual Networks over LinuX (VNX) Project distribution. 
(www: - e-mail: 

Departamento de Ingenieria de Sistemas Telematicos (DIT)
Universidad Politecnica de Madrid

<vnx xmlns:xsi=""
    <automac offset="5"/>
    <vm_mgmt type="none" />
	    <console id="0" display="yes"/>
	    <console id="1" display="yes"/>
  <net name="Net0" mode="virtual_bridge" />
  <!-- NODES -->
  <vm name="ubuntu-gui" type="libvirt" subtype="kvm" os="linux">
    <filesystem type="cow">/usr/share/vnx/filesystems/rootfs_ubuntu-gui</filesystem>
    <if id="1" net="Net0">
    <filetree seq="vnxtxt" root="/tmp">conf/txtfile</filetree>
    <filetree seq="vnxwww" root="/tmp">conf/txtfile</filetree>
    <filetree seq="start-www" root="/var/www">conf/txtfile</filetree>

    <!-- Start xeyes application -->
    <exec seq="xeyes"     type="verbatim" ostype="xexec">xeyes</exec>

    <!-- Start xeyes application and wait until it is closed -->
    <exec seq="xeyes2"    type="verbatim" ostype="xsystem">xeyes</exec>

    <!-- Start gedit, maximize the window and show a text file -->
    <exec seq="vnxtxt"    type="verbatim" ostype="system">chmod 666 /tmp/vnx.txt</exec>
    <exec seq="vnxtxt"    type="verbatim" ostype="xexec">gedit /tmp/vnx.txt</exec>
    <exec seq="vnxtxt"    type="verbatim" ostype="xexec">sleep 3; wmctrl -r vnx.txt -b add,maximized_vert,maximized_horz</exec>
    <exec seq="vnxtxtoff" type="verbatim" ostype="system">pkill gedit; rm /tmp/vnx.*</exec>

    <!-- Start firefox and load vnx.html, copied by means of a <filetree> -->
    <exec seq="vnxwww"    type="verbatim" ostype="system">chmod 666 /tmp/vnx.html</exec>
    <exec seq="vnxwww"    type="verbatim" ostype="xexec">firefox /tmp/vnx.html</exec>
    <exec seq="vnxwwwoff" type="verbatim" ostype="system">pkill firefox; rm /tmp/vnx.*</exec>

    <!-- Start calculator  -->
    <exec seq="calc"      type="verbatim" ostype="xexec">gcalctool</exec>
    <exec seq="calcoff"   type="verbatim" ostype="system">pkill gcalctool</exec>

    <!-- Start/stop apache www server -->
    <exec seq="start-www" type="verbatim" ostype="system">service apache2 start</exec>
    <exec seq="stop-www"  type="verbatim" ostype="system">service apache2 stop</exec>
    <exec seq="start-www2" type="verbatim" ostype="exec">service apache2 start</exec>
    <exec seq="ping"      type="verbatim" ostype="system">'ping'</exec>
    <exec seq="showlog"   type="verbatim" ostype="system">tail -f /var/log/vnxaced.log</exec>
    <exec seq="start-www" type="verbatim" ostype="system">chmod 644 /var/www/*</exec>


    <hostif net="Net0">