Because there aren't any buttons on the front of your virtual machine's beige box, you have to shut down, restart and power off your virtual machine from within the software. These functions can be found by either right-clicking on the running machine, or from the drop-down menu in the toolbar. Depending on the virtualised distribution, both shutdown and restart options should be safe to use.

This is because KVM sends the request to the virtual operating system, and this should handle it in exactly the same way as it would the same option being selected from the shutdown menu in Gnome, or a quick press of the power button in a system that responds correctly to ACPI messages. This means that you'll be warned of the impending shutdown and you'll have a chance to respond to any applications that are still open and save any files.

This won't happen if you choose 'Force Off' from the shutdown menu, as this is the virtual equivalent to pulling the power cable out of the wall. In this case, anything that's not saved to the virtual storage device will be lost.

You may also have noticed a Pause button in the Virt-Manager toolbar. This will instantly stop the virtual machine, which can be resumed from the same point by pressing the Pause button again. But unlike the same functionality in VMware, a paused system will not survive a reboot and you'll lose data held in running applications that haven't saved their state.

Danger – virtualisation ahead

Another important thing to realise is that just because your data is virtual and that there's no power cable to each machine, your work is even more fragile within a virtual environment than it is on your normal desktop. This is because there are more things that can go wrong, and your data is usually harder to get at should you wish to restore it.

It isn't a problem if you manage your data appropriately, but it's something you should be aware of if you start spending a lot of time within a virtual machine.

After running the virtual machine for the first time, you may wonder how you change the disc image to point to another ISO file, or even get back to the same information you saw when you first ran the machine. This configuration panel is accessed from the view panel of the virtual machine you wish to change, and you need to make sure that the machine isn't running to be able to change settings safely.

Just click on View > Details to enter the editor. You will then see a window that offers a comprehensive overview of the virtual hardware being emulated for your machine. Click on IDE CDROM 1, for example, followed by Connect on the panel to the right, and you'll be able to select a new CD/DVD image for your virtual machine. Click on Memory and you can adjust the amount of memory assigned to the machine.

This is handy if you either under-or overestimated how your virtual machine might perform when you ran through the startup wizard.

Check your hardware

You might also want to look at the graphics hardware being emulated. This is found on the Display page, and by default, it's something called 'cirrus'.

The Cirrus Logic chipset that this emulates is one of the most common and broadly compatible chipsets available, with excellent support across a wide range of operating systems. It's perfect for running old distros, MS DOS and even Windows, for example, but it's not the fastest driver, and if you're going to be spending a lot of time in your virtual distribution, it might be worth switching to 'vmvga' in the model list.

This is a close match for VMware's own graphics driver, and is better suited to virtualisation. If your virtualised distribution is able to use an implementation of VMware's open source graphics driver, you should find this option performs better on your system. If not, you can always switch back.

Recent versions of Virt-Manger can also be made to scale the resolution of the virtual machine's display to the size of the window. Just enable the Scale To Display > Always option in the View menu. If you have a virtual screen resolution higher than your host machine's, you will need enable this option or you'll have to manually scroll around the display, which could get a bit wearing.

Another neat function is that your virtual machines are also available through VNC, the remote desktop protocol. To get started with this, take a look at the Display VNC page in the settings viewer.

When your virtual machine is running, you'll see a port listed for the service. You will then be able to access the desktop of your virtual machine using a VNC client, such as Vinagre on Gnome or KFM on KDE. For a client running on the same machine, just point it at localhost:5900 for the first virtual machine. Change the port number to the one listed in the details view if this doesn't work, and you'll see the same desktop session displayed within the Virt- Manager virtual machine view.

This has all kinds of potential uses, from accessing your virtual machines from a remote computer somewhere out in the wilds of the internet to duplicating the desktop for use as a live demonstration with a projector.

Advanced features

You might also have guessed from the Virt-Manager GUI design that you can run as many separate virtual machines as your system will allow. The only real limitation is physical memory, because this is likely to be the weakest link in your system.

When each machine is running simultaneously, you will need enough memory to cater to the specific requirement of each. With 4GB of RAM, for instance, you can run three virtual machines alongside your normal desktop if each were given 1GB of RAM, and you can check the performance of each instance using the CPU meter to the right of each entry in the virtual machine list.

If you need more information on each machine's memory usage, disk throughput and network bandwidth, take a look at the Performance page of the Details window. One of KVM's more advanced features is its ability to access your real hardware through the Physical Host Device functionality.

But before you set your expectations too high, this doesn't mean you can pass your latest high-powered Nvidia graphics card or audio device through to the virtual machine – these are far too complex to work. But you should be able to get most network adaptors to function as well as many USB storage devices.

To get these to work, open the Details window from the virtual machine view and click on the Add Hardware button at the bottom of the list on the left. From the window that appears, select Physical Host Device from the drop-down menu, click on Forward and select the device from the Type and Device lists that appear. Use the Type menu to switch between PCI and USB buses, and the Device list to choose the specific device from the list that appears.

This facility is a little experimental, but you may find that many simpler devices should work without any further modification.