While I’ve switched most of my workloads to Docker, there are still some situations where you need to manage and set up Virtual Machines (VM). These days, KVM+QEMU has more or less been established as the virtualization standard, so we’ll be using that.

Setting this up on Ubuntu 14.04 (Trusty Tahr) is very straight forward. All you need to do is to run:

$ sudo apt-get install qemu-kvm libvirt-bin ubuntu-vm-builder bridge-utils

Assuming everything went well, you should now be up and running and can list your VMs (there are of course none):

$ sudo virsh list
 Id    Name                           State
----------------------------------------------------

If something went wrong, take a look at the KVM installation guide.

If you only need Usermode Networking (i.e. no public IP), you’re done now. If you however need your VMs to be accessible from the outside, you need to set up bridged networking.

With your system up and running, let’s create a VM using vmbuilder:

$ sudo vmbuilder kvm ubuntu \
    --suite trusty \
    --flavour virtual \
    --addpkg=linux-image-generic \
    --addpkg=unattended-upgrades \
    --addpkg openssh-server \
    --addpkg=acpid \
    --arch amd64 \
    --libvirt qemu:///system \
    --user ubuntu \
    --name ubuntu \
    --hostname=test \
    --pass default

Due to this bug, you will need to use the “linux-image-generic” kernel instead of regular virtual one.

Creating the VM will take some time. Once it has been created you can start the VM using virsh with:

$ virsh start test

In order to ssh into the server, we need to find the server IP. There are a few ways to find this, but here’s the best technique I’ve found:

$ sudo virsh dumpxml test | grep 'mac address'
  <mac address='XX:YY:ZZ:XX:YY:ZZ'/>
$ arp -an | grep 'XX:YY:ZZ:XX:YY:ZZ'
  ? (192.168.122.135) at XX:YY:ZZ:XX:YY:ZZ [ether] on virbr0

Next, ssh into the VM:

$ ssh ubuntu@<the VM IP>

The password is defined above as ‘default’

As you probably noticed, those are a fair amount of variables we need to pass onto virsh. The easiest solution to get around this is to create a config file. Porting the variables above into a config file would leave us with something like this:

[DEFAULT]
arch = amd64
user = ubuntu
name = ubuntu
pass = default
tmpfs = -

[ubuntu]
suite = trusty
flavour = virtual
addpkg = openssh-server, unattended-upgrades, acpid, linux-image-generic

[kvm]
libvirt = qemu:///system

With this config file, we can create a VM by simply running:

$ sudo vmbuilder kvm ubuntu -c myfile.cfg

A more complete config file, along with important hooks for re-generating SSH host keys on first boot can be found here.

There’s a lot more to virsh and vmbuilder, but this should help you get started.

Caveats

• In virsh VMs are referred to as ‘domains.’ This might be a bit confusing at first.
• To stop and delete a VM in virsh, run destroy test and then undefine test --managed-save.
• You probably want to use the --mem, --cpus and --rootsize options when using vmbuilder (see the man page).
• Using the --hostname is handy when creating new VMs can be very handy.