Libvirt/QEMU

QEMU

disk creation

# Emulated disk space management (also can shrink, resize an image or store overlay images (see arch-wiki))
qemu-img create -f raw image_file 4G              # Create a raw disk space (`-f qcow2` to utilize dinamically-allocated format)
qemu-img resize disk_image +10G                   # Resize an image (if contains NTFS backup it first)
qemu-img convert -f raw -O qcow2 -o nocow=on input.iso output.qcow2  # specify -o nocow=on if you use btrfs

windows

#!/bin/sh

# sudo qemu-system-x86_64 -drive file=win2016-cli.qcow2,format=qcow2 -m 2G -cpu host -enable-kvm -nic user -vga qxl -spice port=5925,disable-ticketing=on -usbdevice tablet -daemonize


SPICE_PORT=5924
qemu-system-x86_64 -enable-kvm -daemonize \
    -cpu host \
    -drive file=win10-gui.qcow2,if=virtio \
    -nic user \
    -m 8G \
    -bios /usr/share/edk2-ovmf/OVMF_CODE.fd. \
    -vga qxl \
    -spice port=${SPICE_PORT},disable-ticketing=on \
    -usbdevice tablet \
    -device virtio-serial \
    -chardev spicevmc,id=vdagent,name=vdagent \
    -device virtserialport,chardev=vdagent,name=com.redhat.spice.0 \
    "$@"
exec spicy --title Windows 127.0.0.1 -p ${SPICE_PORT}

# drive: aio=native,cache.direct=on
# cpu:   hv_relaxed,hv_spinlocks=0x1fff,hv_vapic,hv_time
# -net nic -net user,hostname=windowsvm    --->  -nic user

Libvirt

Prerequisites

usermod -aG libvirt myuser

rc-service libvirtd start
# OR 
systemctl start libvirtd

virt-install

# define domain from iso (create a qcow2 image first)
qemu-img create -f qcow2 debian-1.qcow2 10G
virt-install --name debian-test-2 --memory 1000 --vcpus 2 --osinfo debian12 --disk path=./debian12-1.qcow2,format=qcow2 --cdrom ~/Downloads/debian-12.5.0-amd64-netinst.iso --network network=default

# import an already existing qcow2 image
virt-install --name debian-test-2 --memory 1000 --vcpus 2 --osinfo debian12 --disk path=./debian12-1.qcow2,format=qcow2 --import

# query all available osinfo types
virt-install --osinfo list

Windows domain installation example:

home=/home/fuser/virt
name="Windows-Server-2016-2"
memmax=6144 # in Mb
cpu=2
disk_path=$home/ActiveDirectoryLab/$name.img
disk_size=51.2 # In Gb
cdrom_path=$home/iso-cdrom/Windows_Server_2016_Datacenter_EVAL_en-us_14393_refresh.ISO
# cdrom_path=$home/iso-cdrom/Win10_22H2_English_x64v1.iso
virtio_path=$home/iso-cdrom/virtio-win-0.1.240.iso
os_type=windows
os_variant=win2k12r2
# os_variant=win10

/usr/bin/virt-install \
  --connect qemu:///system \
  --name=$name \
  --ram=$memmax \
  --vcpus=$cpu \
  --cpu host \
  --cdrom=$cdrom_path \
  --os-type=$os_type \
  --os-variant=$os_variant \
  --disk path=$disk_path,device=disk,bus=virtio,size=$disk_size,format=qcow2 \
  --disk path=$virtio_path,device=cdrom --force \
  --boot uefi,cdrom,hd,menu=on \
  --network bridge=virbr5,model=e1000e \
  --graphics vnc,listen=0.0.0.0 \
  --video=qxl \
  --accelerate \
  --noautoconsole \
  --hvm

MT-CHR installation

# unarchive
unzip ~/Downloads/chr-7.16.1.vmdk.zip
# convert to qcow2
qemu-img convert -f vmdk -O qcow2 chr-7.16.1.vmdk chr-7.16.1.qcow2
# boot from it (note the --import parameter, this tells qemu to use --disk as a boot drive)
virt-install --name=mt-chr-1 --vcpus=1 --memory=512 --disk path=./chr-7.16.1.qcow2,format=qcow2 --network=network:suricata_sniff --osinfo debian12 --import

resize qcow2 partition

virt-resize --expand /dev/sda4 fcos-1.qcow2 fcos-2.qcow2

`emulator does not support machine type` error

qemu-system-x86_64 -machine help
# find your machine type in there, if it's not present find the latest 
# and then edit xml to change the machine type
virsh edit Windows-10-Desktop-2
# change the value under <type machine="XXX"> to either the one listed under `-machine help`

change pool location

virsh shutdown my-vm-name
rsync -a /var/lib/libvirt/images/my-vm-name /var/lib/libvirt/new-dir/
virsh edit my-vm-name
(within edit window)--> :s/\/var\/lib\/libvirt\/images/\/var\/lib\/libvirt\/new-dir/g
virsh start my-vm-name

delete domain completely

virsh destroy _domain-id_
virsh undefine _domain-id_

virsh vol-list --pool k8s_lab
# Name                                              Path
# ----------------------------------------------------------------------------------------------------------------------------
# coreos-1                                          /home/spil/virt/k8s_lab/coreos-1
# fedora-coreos-41.20250105.3.0-qemu.x86_64.qcow2   /home/spil/virt/k8s_lab/fedora-coreos-41.20250105.3.0-qemu.x86_64.qcow2
virsh vol-delete --pool vg0 _domain-id_.img

`virsh start` permission denied error

sudo usermod -a -G kvm myusername

### /etc/libvirt/qemu.conf
user = "myusername"
group = "kvm"

get dnsmasq definitions for the vnet

sudo ls -la /var/lib/libvirt/dnsmasq/fcos*
# -rw-r--r--. 1 root root 104 Jul 22 18:30 /var/lib/libvirt/dnsmasq/fcos_k8s_lab.addnhosts
# -rw-------. 1 root root 673 Jul 22 18:29 /var/lib/libvirt/dnsmasq/fcos_k8s_lab.conf
# -rw-r--r--. 1 root root 172 Jul 22 18:30 /var/lib/libvirt/dnsmasq/fcos_k8s_lab.hostsfile

rename a domain

virsh dumpxml $DOMAIN > $SOMEFILE.xml
virsh undefine $DOMAIN
vim $DOMAIN.xml
virsh define $DOMAIN.xml
virsh destroy $DOMAIN
virsh start $DOMAIN

allocate memory to a domain

virsh destroy $DOMAIN
virsh setmaxmem $DOMAIN 3G --config
virsh setmem $DOMAIN 3G --config
virsh start $DOMAIN

allocate vcpu to a domain

virsh setvcpus $DOMAIN 3 --config --maximum
virsh setvcpus $DOMAIN 3 --config

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