How to Setup KVM on Ubuntu Lucid

More than a year ago I wrote an article about Xen on Ubuntu Intrepid with the intention of blaming Ubuntu. I also clearly said, that I wouldn’t use Ubuntu anymore. This article turned out to be the most hit one on my blog. Maybe because the Ubuntu community directly links to it. Then, last Summer I wrote an article about alternatives to Xen, but I decided to wait and stay with Xen on my homeserver in the meantime. (Please keep in mind, all I use this for is for my private setups!). Last week I upgraded my Server’s hardware and also wanted to re-install it.

Xen still hasn’t made it into vanilla Kernel, it might make it into 2.6.34 or .35, but even if it does, I think it’s not even going to be close to being production ready. Plus most distributions release their next version in the next weeks/months and are already frozen, so they definitely will not ship with Xen. Well, the only real alternative is KVM. I didn’t like the idea of using KVM for a long time, but since almost every distribution now features KVM as their virtualization technique, I went with it. I also went with Ubuntu again (yeah blame me!). Why? Because their next release has long-term support, and I won’t have the time to upgrade it in the next 12-18 months. And what shall I say… I like it. Installation was kinda tricky on a software Raid0, but I was installing a development release, 1 week before the first Beta… and in the end it did work.

The server runs KVM now and it runs fast and stable. I have 4 virtual machines on it now. Installation of the guests using virt-installer and/or ubuntu-vm-builder was much easier and ended up with working VMs out of the box, whereas xen-create-image ended up with an unusable image on Intrepid, because the default console never showed up without tweaks. libvirt is also nice if you need it, but I really want to point out, that you can run KVM without libvirt just with the ‘kvm’ command!

I tagged this article ‘How-To’, but there are already many good KVM guides out there so I won’t write yet another one. I’ll just post a few hints to get KVM running with a bridged networking using libvirt.

First of all I removed /etc/libvirt/qemu/networks/default.xml to disable the dnsmasq features of libvirt. Then I created an LVM volume group where I wanted to place my machines at, but you can also use simple images on your filesystem. The next thing I did was setting up a bridge in /etc/network/interfaces:

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auto br1
iface br1 inet dhcp
        bridge_ports eth1
        bridge_stp off
        bridge_fd 0
        bridge_maxwait 0

You can now simply create your virtual machine with this command:

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virt-install -n $hostname -r 512 -c /home/shared/apps/os/ubuntu/lucid-server-amd64.iso --disk path=/dev/virtdisks/bender --network bridge=br1 --vnc --vnclisten=0.0.0.0 --noautoconsole --os-type linux --os-variant ubuntuLucid --accelerate

Now connect to your host using VNC and install as usual. Another way is to use ‘ubuntu-vm-builder’, but I simply didn’t try… Make sure you limit VNC access to localhost in /etc/libvirt/qemu/$hostname.xml after installation if your network is unsecure.

To make your domain autostart on boot use:

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virsh autostart $hostname

This will copy the appropriate xml configuration file to /etc/libvirt/qemu/autostart/.

It’s as simple as that. Way easier than patching a kernel for Xen and all these things. I would have really loved to see Xen in vanilla Kernel a year ago or so, but it didn’t happen and KVM works well enough for me by now… plus you have the benefit of a working power-management.