Creating virtual machines in libvirt with virt-install

Dec 16, 2016 · 4 minute read · Comments
libvirt linux virtualization console

I’ve been wanting to automate my virtual machine instantiation for a while now, but I’ve always hated the idea of having to spin up multiple bits of infrastruction to deal with PXE booting, web server to host a kickstart file, etc. Luckily, I ran into some stuff today, and figured out how to automate virtual machine instantitation without having to resort to anything outside of localhost.

Preface

I have an LVM logical volume that hosts my virtual machines my M.2 disk drive, and everything else on the host running from the SSD. This means that I have /var/lib/libvirt/images/ mounted to my M.2 drive, and everything else on the SSD (except for swap as well).

Originally I was trying to get all this working with the user session, but the user doesn’t have permission to make networking changes and to attach to the bridged network. A few things on the internet seemed to indicate running as a user wasn’t possible because of this. I suspect there are some permissions things and SElinux tweaks I could do to make it work, but path of least resistence for now is how it’ll be.

That just means the following commands are going to be run with sudo. Of course if you are just going to use the default network then you might be able to get away with doing some of this in a user session.

Using `virt-install`

Using the virt-install application we can instantitate a virtual machine from the console. I got this all working by running the following command:

sudo virt-install --name testing --memory 1024 \
    --disk /var/lib/libvirt/images/testing.qcow2,size=20,bus=virtio \
    --cdrom /var/lib/libvirt/isos/centos7.iso \
    --boot cdrom \
    --network bridge=br0 \
    --noautoconsole --vnc

If we look at this command, it defines the following things:

virtual machine is named testing
we define 1024 MB of memory (RAM) to this VM
the VM will use a qcow2 backing disk with a size of 20GB, over the virtio bus
we’ll mount the centos7.iso into the CDROM (boot media)
tell the system to boot from the CDROM
assign the network to bridge to interface br0
don’t start a console, and enable VNC

I originally did this so that 1) I could validate that everything was going to work :) and 2) so that I could perform a minimal install to generate my initial anaconda-ks.cfg file (kickstart file).

After installation, I scp’d the file down to my host and moved onto the next step. Automation ftw!

Automating our virtual machine instantiation

Next up we just need to make a couple changes to our virt-install command so that we use the new kickstart file for our deployment. First though, we need to add a reboot value to the default anaconda-ks.cfg file.

Kickstart file

The following is the default generated kickstart file from a CentOS 7 minimal install.

You’ll see that I’ve added reboot right after the clearpart command, and just before the %packages command.

#version=DEVEL
# System authorization information
auth --enableshadow --passalgo=sha512
# Use CDROM installation media
cdrom
# Use graphical install
graphical
# Run the Setup Agent on first boot
firstboot --enable
ignoredisk --only-use=vda
# Keyboard layouts
keyboard --vckeymap=us --xlayouts='us'
# System language
lang en_US.UTF-8

# Network information
network  --bootproto=dhcp --device=eth0 --ipv6=auto --activate
network  --hostname=localhost.localdomain

# Root password
rootpw --iscrypted <ENCRYPTED_PASSWORD>
# System services
services --enabled="chronyd"
# System timezone
timezone America/New_York --isUtc
user --groups=wheel --name=stack --password=<ENCRYPTED_PASSWORD> --iscrypted --gecos="stack"
# System bootloader configuration
bootloader --append=" crashkernel=auto" --location=mbr --boot-drive=vda
autopart --type=lvm
# Partition clearing information
clearpart --none --initlabel

reboot

%packages
@^minimal
@core
chrony
kexec-tools

%end

%addon com_redhat_kdump --enable --reserve-mb='auto'

%end

%anaconda
pwpolicy root --minlen=6 --minquality=50 --notstrict --nochanges --notempty
pwpolicy user --minlen=6 --minquality=50 --notstrict --nochanges --notempty
pwpolicy luks --minlen=6 --minquality=50 --notstrict --nochanges --notempty
%end

Kickstart-based virtual machine instantiation

And here is our modified virt-install line which will get you a CentOS 7 virtual machine created. Once the installation completes, the VM will shut down, and you can start it back up with sudo virsh start <machine_name>.

Here is the command that will install your VM for you using the local kickstart file.

sudo virt-install --name testing --memory 1024 \
    --disk /var/lib/libvirt/images/testing.qcow2,size=20,bus=virtio \
    --location /var/lib/libvirt/isos/centos7.iso \
    --boot cdrom \
    --network bridge=br0 \
    --noautoconsole --vnc \
    --initrd-inject anaconda-ks.cfg \
    --extra-args "inst.ks=file:/anaconda-ks.cfg"

Leif Madsen