KVM is a full virtualization solution for Linux on x86 (64-bit included) hardware containing virtualization extensions (Intel VT or AMD-V). It consists of a loadable kernel module, kvm.ko, that provides the core virtualization infrastructure and a processor specific module, kvm-intel.ko or kvm-amd.ko.
Under Lenny, the Debian package name is 'kvm'. Under Squeeze, it is 'qemu-kvm'. See README.Debian.gz in the qemu-kvm package on Squeeze for an explanation of the name change. Install the correct kvm package with apt-get or aptitude, e.g. using this command:
aptitude install qemu-kvm libvirt-bin
The daemon libvirt-bin daemon will start automatically at boot time and load the appropriate kvm modules, kvm-amd or kvm-intel, which are shipped with the Linux kernel Debian package. If you intend create VMs from the command-line, install virtinst.
In order to be able to manage virtual machines as regular user you should put this user into the libvirt group:
adduser <youruser> libvirt
Setting up bridge networking
Managing VMs from the command-line
You can then use the virsh(1) command to start and stop virtual machines. VMs can be generated using virtinst. For more details see the libvirt page. Virtual machines can also be controlled using the kvm command in a similar fashion to QEMU.
Managing VMs with a GUI
On the other hand, if you want to use a graphical UI to manage the VMs, you can use the Virtual Machine Manager virt-manager.
Migrating guests to a Debian host
Migrating guests from RHEL/CentOS 5.x
There are a few minor things in guest XML configuration files (/etc/libvirt/qemu/*.xml you need to modify:
Machine variable in <os> section should say pc, not rhel5.4.0 or similar
Emulator entry should point to /usr/bin/kvm, not /usr/libexec/qemu-kvm
In other words, the relevant sections should look something like this:
<os> <type arch='x86_64' machine='pc'>hvm</type> --- snip --- <devices> <emulator>/usr/bin/kvm</emulator>
If you had configured a bridge network on the CentOS host, please refer to this wiki article on how to make it work on Debian.
No network bridge available
virt-manager uses a virtual network for its guests, by default this is routed to 192.168.122.0/24 and you should see this by typing ip route as root.
If this route is not present in the kernel routing table then the guests will fail to connect and you will not be able to complete a guest creation.
Fixing this is simple, open up virt-manager and go to "Edit" -> "Host details" -> "Virtual networks" tab. From there you may create a virtual network of your own or attempt to fix the default one. Usually the problem exists where the default network is not started.
cannot create bridge 'virbr0': File exists:
To solve this probelm you may remove the virbr0 by running:
brctl delbr virbr0
Open virt-manager and go to "Edit" -> "Host details" -> "Virtual networks" start the default network.
You can check the netstatus
virsh net-list --all
Optionally, you can use bridge network BridgeNetworkConnections
http://www.linux-kvm.org/ - Kernel Based Virtual Machine homepage;
http://web.archive.org/web/20080103004709/http://kvm.qumranet.com/kvmwiki/Debian - KVM on Debian Sid (old KVM wiki)