KVM, CoreOS and LVM

2013-11-06 by Quinlan Pfiffersoftware

This is a little tutorial on how I got the official CoreOS image working with KVM.

Setting up the Virtual Machine

1. Download the image. You can get it here.
2. You need to convert the image to it’s raw data so that you can extract it to your LVM.

bunzip2 coreos_production_qemu_image.img.bz2
qemu-img convert coreos_production_qemu_image.img -O raw coreos.raw

1. Once thats done converting, take your raw data and dd it onto your LVM.

dd if=coreos.raw of=/dev/lvmgroup/lvm_name

1. Create your machine with whatever specs you want, at the time of this writing the CoreOS image is about 6GB or so. I used virt-manager to get it done quickly.

SSH Keys

CoreOS has some funky ideas about users and ssh keys, so I had to figure out how to pass through the keys. Turns out with virt-manager, you can add these pretty easily through the interface.

You’ll need your known authorized_keys file setup beforehand, which I won’t cover. Place it somewhere your libvirt user can read and access. I threw mine in /var/lib/libvirt/ssh.

Then just add the following XML to your KVM’s definition, which should be in /etc/libvirt/qemu.

<filesystem type='mount' accessmode='passthrough'>
    <source dir='/var/lib/libvirt/ssh'/>
    <target dir='metadata'/>
    <readonly/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
</filesystem>

and then once thats done:

virsh define /etc/libvirt/machine_name.xml

This adds a filesystem passthrough to your virtual machine that will add a ‘metadata’ tag, which can be mounted. The virt-manager interface is a little misleading in this regard.

At the end of all this, you should be able to ssh as core into your new machine.