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Virsh

Virtual Machine Management

Before you Begin

  1. Add yourself to the qemu and libvirt groups: usermod -aG libvirt,qemu ducoterra
  2. Change the images ownership to qemu: chown -R qemu:qemu /var/lib/libvirt/images
  3. Change the iso ownership to qemu: chown -R qemu:qemu /var/lib/libvirt/iso
  4. Allow group write access to images: chmod 770 /var/lib/libvirt/images
  5. Allow group write access to iso: chmod 770 /var/lib/libvirt/iso
  6. Tell virsh to connect to your root system rather than your user: export LIBVIRT_DEFAULT_URI='qemu:///system'
  7. Export your editor so virsh knows what to use: export EDITOR=vim

Connecting to External Servers via SSH

https://libvirt.org/uri.html#ssh-transport

Configuring Aliases

  1. Edit ~/.config/libvirt/libvirt.conf

  2. Add your aliases

    uri_aliases = [
    "3dserver=qemu+ssh://3dserver/system",
]

  3. Export the alias: export LIBVIRT_DEFAULT_URI=3dserver

One-off Connections

export LIBVIRT_DEFAULT_URI='qemu+ssh://user@server/system'

Useful Virsh Commands

# Show node info
virsh nodeinfo

# List OS variants
osinfo-query os

# List all current machines
virsh list --all

# Connect to console VM
virsh console fedora42-test

# Connect to graphical VM
virt-viewer --wait fedora42-test

# Get leased IP Addresses for the default network
virsh net-dhcp-leases default

# Reboot a VM
virsh reboot <domain>

# Shutdown a VM
virsh shutdown <domain>

# Force shutdown a VM
virsh destroy <domain>

# Remove a VM
virsh undefine --nvram <domain>

# Remove a VM including storage
virsh undefine <domain> --nvram --remove-all-storage

Virsh Networking

Create a Virtual Network

Creating a new network will require an XML configuration file. To see the default network's configuration, use

virsh net-dumpxml default > virbr0.xml

To create a dual-stack network, use the following. (Note, I generated a unique local ipv6 address here).

<network>
  <name>dual-stack</name>
  <forward mode="nat"/>
  <domain name="dual-stack"/>
  <ip address="192.168.100.1" netmask="255.255.255.0">
    <dhcp>
      <range start="192.168.100.2" end="192.168.100.254"/>
    </dhcp>
  </ip>
  <ip family="ipv6" address="fd4d:58e7:17f6:1::1" prefix="64"/>
</network>

I've already defined this network in active/software_virsh/dual-stack-dhcp.xml. Install it with

# Define and autostart the network
virsh net-define active/software_virsh/dual-stack-dhcp.xml
virsh net-start dual-stack-dhcp
virsh net-autostart dual-stack-dhcp

# List networks to ensure it created
virsh net-list --all

# Get the UUID of the created network
virsh net-uuid dual-stack-dhcp

Attach a New Virtual Network

export VM_NAME=my_vm
virsh attach-interface \
--type bridge \
--source virbr1 \
--model virtio \
--config \
--live \
--domain ${VM_NAME}

Detach a Virtual Network

# List mac addresses of connected interfaces'
export VM_NAME=my_vm
virsh domiflist --domain $VM_NAME
virsh detach-interface --domain k0s-worker0 --type bridge --mac "52:54:00:f6:b9:83" --live

Destroy a Virtual Network

export NETWORK_NAME=mynetwork
virsh net-undefine --network $NETWORK_NAME
virsh net-destroy --network $NETWORK_NAME

Set a Static IP

To set a static IP, run virsh net-edit default and add the following between <dhcp> and </dhcp>

# Add a host
virsh net-update default add-last ip-dhcp-host \
      '<host mac="52:54:00:6f:78:f3" ip="192.168.122.222"/>' \
      --live --config --parent-index 0

# Modify a host
virsh net-update default modify ip-dhcp-host \
      '<host mac="52:54:00:6f:78:f3" ip="192.168.122.222"/>' \
      --live --config --parent-index 0

# Delete a host
virsh net-update default delete ip-dhcp-host \
      '<host mac="52:54:00:6f:78:f3" ip="192.168.122.222"/>' \
      --live --config --parent-index 0

Creating VMs

If you have an osbuild image you can run the following to generate a qcow2 disk image. Then you can create a VM with an existing qcow2 disk and skip the installation process altogether.

sudo systemctl start osbuild-composer.socket
composer-cli compose list
export IMAGE_UUID=
export VM_DISK_PATH=/var/lib/libvirt/images/fedora43-test.qcow2
composer-cli compose image --filename ${VM_DISK_PATH} ${IMAGE_UUID}

Create VM with No Graphics and use an Existing QCOW2 Disk

# Start the  default network if it isn't already
virsh net-start --network default

export VM_NAME="fedora43-test"
export VM_DISK_PATH=/var/lib/libvirt/images/fedora43-test.qcow2

# OPTIONAL: export your qcow2 disk now if using osbuild
export IMAGE_UUID=
composer-cli compose image --filename ${VM_DISK_PATH} ${IMAGE_UUID}

# Install
# `--location /path/to/image.iso` supplies a disk installer. (Remove `--import`)
# `--import` skips the installation process.
# `--graphics spice --video qxl,model.ram=131072,model.vram=131072,model.vgamem=131072 --channel spicevmc` installs graphics
# `--console pty,target.type=virtio` adds a console connection
# For any command, use `virt-install --arg=?` to see all available options
virt-install \
--name "${VM_NAME}" \
--boot uefi,firmware.feature0.name=secure-boot,firmware.feature0.enabled=no \
--cpu host-passthrough --vcpus sockets=1,cores=8,threads=2 \
--ram=8192 \
--os-variant=fedora41 \
--network bridge:virbr0 \
--graphics none \
--console pty,target.type=virtio \
--import --disk "path=${VM_DISK_PATH},bus=virtio"

Create a Cloud Init Compatible VM

https://cloudinit.readthedocs.io/en/latest/reference/examples.html

# Fedora
# https://fedoraproject.org/cloud/download
export VM_NAME="cloud-init-test-fedora"
export VM_DISK_PATH=/var/lib/libvirt/images/Fedora-Cloud-Base-Generic-43-1.6.x86_64.qcow2

# Rocky
# https://rockylinux.org/download
export VM_NAME="cloud-init-test-rocky"
export VM_DISK_PATH=/var/lib/libvirt/images/Rocky-10-GenericCloud-Base.latest.x86_64.qcow2

# Ubuntu
# https://cloud-images.ubuntu.com/noble/current/
export VM_NAME="cloud-init-test-ubuntu"
export VM_DISK_PATH=/var/lib/libvirt/images/noble-server-cloudimg-amd64.img

# Debian
# https://cloud.debian.org/images/cloud/trixie/20251117-2299/
export VM_NAME="cloud-init-test-debian"
export VM_DISK_PATH=/var/lib/libvirt/images/debian-13-generic-amd64-20251117-2299.qcow2

# Set --cloud-init disable=no to allow cloud-init to run again after first boot
virt-install \
--name "${VM_NAME}" \
--boot uefi,firmware.feature0.name=secure-boot,firmware.feature0.enabled=no \
--cpu host-passthrough --vcpus sockets=1,cores=8,threads=2 \
--ram=8192 \
--os-variant=fedora41 \
--network bridge:virbr0 \
--graphics none \
--import --disk "path=${VM_DISK_PATH},bus=virtio" \
--cloud-init disable=yes,user-data="active/software_virsh/cloud-init/user-data,meta-data=active/software_virsh/cloud-init/meta-data"

Create VM with Graphics using an ISO Installation Disk

# `--cdrom /path/to/image.iso` supplies a disk installer. (Remove `--import`)
# `--import` skips the installation process.
# `--graphics spice --video qxl --channel spicevmc` installs graphics
# `--console pty,target.type=virtio` adds a console connection
# For any command, use `virt-install --arg=?` to see all available options
export VM_NAME="fedora43-kinoite-test"
export VM_ISO_PATH=/var/lib/libvirt/iso/fedora43.iso
export VM_DISK_PATH=/var/lib/libvirt/images/fedora43.qcow2
virt-install \
--name "${VM_NAME}" \
--boot uefi,firmware.feature0.name=secure-boot,firmware.feature0.enabled=no \
--cpu host-passthrough --vcpus sockets=1,cores=8,threads=2 \
--ram=8192 \
--os-variant=fedora41 \
--network bridge:virbr0 \
--graphics spice --video virtio --channel spicevmc \
--cdrom ${VM_ISO_PATH} \
--disk "path=${VM_DISK_PATH},size=64,bus=virtio,format=qcow2"

Create VM using Host Device as Disk

# `--cdrom /path/to/image.iso` supplies a disk installer. (Remove `--import`)
# `--import` skips the installation process.
# `--graphics spice --video qxl --channel spicevmc` installs graphics
# `--console pty,target.type=virtio` adds a console connection
# `--hostdev 0x1234:0x5678` adds a block storage device
# For any command, use `virt-install --arg=?` to see all available options
export VM_NAME="usb-linux"
virt-install \
--name "${VM_NAME}" \
--boot uefi,firmware.feature0.name=secure-boot,firmware.feature0.enabled=no \
--import \
--cpu host-passthrough --vcpus sockets=1,cores=8,threads=2 \
--ram=8192 \
--os-variant=fedora41 \
--network bridge:virbr0 \
--graphics spice --video qxl --channel spicevmc \
--hostdev 0x13fe:0x6500,boot.order=1 \
--disk none

Snapshots

See qemu qcow2 snapshots

Virt Builder

https://docs.fedoraproject.org/en-US/fedora-server/virtualization/vm-install-diskimg-virtbuilder/#_minimal_effort_customization

You can use virt-builder to build vm images

export VM_NAME=fedora42-vb
export VM_DISK_PATH=/var/lib/libvirt/images/fedora42-vb.qcow2

# Build the image
virt-builder fedora-42 \
--format qcow2 --output ${VM_DISK_PATH} \
--root-password locked:disabled \
--hostname ${VM_NAME} \
--selinux-relabel \
--firstboot-command 'useradd -m -G wheel -p "" ducoterra ; chage -d 0 ducoterra'

# Run the built image
virt-install \
--name "${VM_NAME}" \
--cpu host-passthrough --vcpus sockets=1,cores=8,threads=2 \
--ram=8192 \
--os-variant=fedora41 \
--network bridge:virbr0 \
--graphics none \
--console pty,target.type=virtio \
--import --disk "path=${VM_DISK_PATH},bus=virtio"
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