No blog entry since 2019 🙈🙈🙈
So let me share something small yet hopefully helpful. Mostly I try to do everything in containers but now I am in a project that uses ansible to deploy software to machines so I thought it might be better to spin up a VM. As it is 2022 I thought I should do it without using VMWare, Virtualbox etc. Instead I wanted to work with
libvirt and start a
cloud-init capable image to not have to click through some installation process.
Unfortunately this is not as easy as one would think and took me quite a while to figure out. There are many references where this takes many steps. I hope this quick post gets you started faster.
On an arch linux (btw I use Arch) you need to have the following packages installed:
sudo pacman -S libvirt qemu-system-x86 virt-install
And libvirtd must be started:
sudo systemctl start libvirtd
Then make sure your user is in group
libvirt so it is allowed to manage VMs.
Download the image
First of all download the appropriate generic for the image here: https://cloud.debian.org/images/cloud/
In case you want bullseye on amd64 here is the direct link: https://cloud.debian.org/images/cloud/bullseye/latest/debian-11-generic-amd64.qcow2
DO NOT DOWNLOAD THE GENERICCLOUD IMAGE (explanation later)
Put it here:
Preparing a cloud init file
The debian image doesn't have a default user (contrary to for example ubuntu) so we need to create one during bootup.
#cloud-config users: # whatever username you like - name: mop # so our user can just sudo without any password sudo: ALL=(ALL) NOPASSWD:ALL shell: /bin/bash # content from $HOME/.ssh/id_rsa.pub on your host system ssh_authorized_keys: - ssh-rsa AAAA[...]
Cloud init supports pulling keys from github directly. Unfortunately that didn't work for me in the debian cloud image (ubuntu worked 🤔). Probably debian just has an old version.
Starting the VM
virt-install --name debian --memory 2048 --vcpus 4 --disk=size=10,backing_store=/var/lib/libvirt/images/debian-11-generic-amd64.qcow2 --cloud-init user-data=./cloud-init.yaml,disable=on --network bridge=virbr0 --osinfo=debian11
This starts a new VM and a console will come up showing the boot process and the IP that the VM is using in bridge mode. (or just issue a
ip neigh on your host system). If you want to leave the console press
Ctrl+] (there is also an
--noautoconsole option for virt-install if you want it to boot in the background). You should now be able to login using the console and you should be able to ssh to the VM.
--disk option is quite interesting. This uses an overlay filesystem much like docker. So the general image is shared across all future debian VMs but the changes per VM will be saved in a separate images in this directory:
Obviously there are many things here that you can change/adjust but this is just the most simple command line that worked for me. Details can be found in the man page of
Getting rid of the VM
This is also non-intuitive.
First you have to stop the machine:
virsh destroy --domain debian
And then delete it using
virsh undefine --domain debian --remove-all-storage
This will remove the overlay filesystem containing all your changes to your VM but keep the base image.
I like how libvirtd uses special terms for everything.
destroy instead of
domain instead of
undefine instead of
The genericcloud debian image
genericcloud: Similar to generic. Should run in any virtualised environment. Is smaller than
genericby excluding drivers for physical hardware.
Obviously this sounds like the right image. Unfortunately it is not. It doesn't contain the SATA AHCI drivers which are needed because of the way the cloud-init stuff is being injected into the VM (as a cdrom drive).
This took me a quite a while to figure out. After finding out what was the culprit I was finally able to google for the problem and found this: https://groups.google.com/g/linux.debian.bugs.dist/c/fpGNuIC7GZc