VM with libvirt

Requirements:

apt-get install qemu qemu-kvm libvirt-clients libvirt-daemon-system virtinst bridge-utils

Note: on debian12, qemu becomes qemu-sytem

And vmx compatibility: grep -E --color 'vmx|svm' /proc/cpuinfo

Build an image

with Virt-builder

Debian package: libguestfs-tools

virt-builder debian-11 -o test.img --size 100G --root-password password:XXX --hostname test.parmentier.io --install "net-tools" --append-line '/etc/resolv.conf:nameserver 213.186.33.99'

Notes:

you can use --firstboot-command 'apt-get install -y ...'
--append-line '/etc/hosts:192.168.225.1 server.ostechnix.local'

source

Install an image

Debian package: virtinst

virt-install \
--name test.parmentier.io \
--ram 4096 \
--disk path=/var/lib/libvirt/images/test.img \
--vcpus 2 \
--os-variant debian10 \
--network bridge=br0,mac=xxx \
--graphics none \
--noautoconsole \
--boot hd \
--import

Notes:

there is no --os-variant debian11 yet, but debian10 should be fine?
if you use a bridge network, ensure it is configured on host, and you might have to specify a virutal mac address (its the case for ovh vm within dedicated).
If you are trying to install an iso from scratch, you will certainly need --cdrom=/path/to/file.iso and --graphics vnc see example

source

Start vm

virsh --connect qemu:///system start test.parmentier.io

Auto start

virsh autostart test.parmentier.io

Get into vm

virsh console test.parmentier.io

Edit configuration

virsh edit test.parmentier.io

Note: in some configuration (e.g. cpu) you will have to shutdown/start. See also examples

Uninstall

virsh shutdown test.parmentier.io
virsh undefine test.parmentier.io

Reboot safely

virsh reboot test.parmentier.io

Hard reboot

virsh reset test.parmentier.io

Other useful commands

suspend: froze on memoryy
shutdown
destroy: try shutdown first
dominfo: get info such as cpu, memory

Network (host)

On debian 11, ensure apt-get install -y bridge-utils:

iface eno3 inet manual

auto br0
iface br0 inet static
    address xx/24
    gateway yyy
    bridge-ports eno3
    bridge-stp off
    bridge-fd 0
    hwaddress 0a:xx:00

Note:

on debian 11, without mac address, it did not work. You can check available bridges with brctl show
on debian 12 (ovh template) I was not able to make it works. I played with source 1 and source 2 unsucessfully. It was like if interfaces was not taken in consideration, as well as cloud.cfg in networksection. I will try it when I have dedicated time.

Also, ensure you have ip_forward=1, you cna check value with sysctl net.ipv4.ip_forward, and edit with sysctl net.ipv4.ip_forward=1. To make it persistant: edit /etc/sysctl.conf, find the line ip_forward=, then run sysctl -p /etc/sysctl.conf.

source 1
source2
source3
man bridge-utils-interfaces

Network (vm)

auto enp1s0
iface enp1s0 inet static
        address xx
        netmask 255.255.255.255
        broadcast xx
        post-up ip route add yy/32 dev enp1s0
        post-up ip route add default via yy
        pre-down ip route del yy/32 dev enp1s0
        pre-down ip route del default via yy

Note: replace xx and yy

Filesystems

virt-filesystems -a test.img --all --long -h

Export/Import VM

Export

# virsh configuration file
virsh dumpxml test.parmentier.io >test.parmentier.io.xml

# list of image(s) 
virsh domblklist test.parmentier.io

Transfert on other machine

reduce sparse space with tar cvf parmentier.img >parmentier.img.tar
use --inplace with rsync

source

Note: on case you did not realized this step, you can use virt-sparsify (you can use --in-place if it is not used)

Import

virsh define test.parmentier.io.xml

Note: you will certainly need to update network (post-up ip route add rule) in order to use the host bridge ip.

Web UI

cockpit

Expanding or Shrinking an image

Note: I only try to shrink an image, and it did not work.

See current usage:

virt-df -h -a /var/lib/libvirt/images/test.img

Resize it:

virt-resize --resize /dev/sda1=-50G test.img new-test.img

Note: backup the image is highly recommended before any action

source 1

source 2

source 3