Managing Virtual Machines On Xen: A Getting Started Guide

Xen remains a robust hypervisor for production environments—AWS EC2, Citrix Hypervisor, and many hosting providers still rely on it. However, KVM has become the default for most Linux distributions due to simpler management and better integration with standard tooling. For new deployments on standard Linux, evaluate KVM with libvirt or container solutions like Docker and Kubernetes. That said, if you’re working with existing Xen infrastructure or need its advanced features, here’s how to create and manage virtual machines.

File-Backed Virtual Block Devices

File-backed VBDs are practical for testing and small deployments. They’re easy to duplicate—just copy the file and update the configuration. For production, consider LVM-backed or real block devices for better performance.

Create a 20GB sparse file-backed VBD:

truncate -s 20G vmdisk0

Or with dd if you prefer:

dd if=/dev/zero of=vmdisk0 bs=1M seek=20480 count=1

Format with ext4 (ext3 is obsolete):

mkfs.ext4 vmdisk0

Installing a DomU via PXE

Download the kernel and initrd for your distribution. For Fedora 41:

wget https://mirrors.kernel.org/fedora/releases/41/Server/x86_64/os/images/pxeboot/vmlinuz
wget https://mirrors.kernel.org/fedora/releases/41/Server/x86_64/os/images/pxeboot/initrd.img

Create an installation profile f41-install.cfg:

name = "f41-install"
memory = 1536
vcpus = 2
disk = [ 'file:/home/xen/vmdisk0,xvda,w' ]
vif = [ 'bridge=xenbr0' ]
kernel = "/home/xen/fedora/vmlinuz"
ramdisk = "/home/xen/fedora/initrd.img"
extra = "ip=dhcp"
on_reboot = 'restart'
on_crash = 'restart'

If your Xen toolstack supports blktap2, use tap:aio: instead of file: for better performance. However, blktap2 is deprecated in newer Xen versions—stick with file: for compatibility.

Start the VM:

xl create f41-install.cfg

Note: Modern Xen uses xl instead of the older xm command. xm is deprecated and may not exist in recent distributions.

Connect to the console:

xl console f41-install

Complete the installation using the network. Typical Fedora mirrors work fine.

Persistent DomU Configuration

After installation, create a run profile vm1.cfg:

name = "vm1"
memory = 1536
vcpus = 2
disk = [ 'file:/home/xen/vmdisk0,xvda,w' ]
vif = [ 'bridge=xenbr0' ]
bootloader = "/usr/lib/xen/boot/pygrub"
on_reboot = 'restart'
on_crash = 'restart'

PyGrub reads the guest’s bootloader configuration, allowing the DomU to manage its own kernel updates without Dom0 intervention.

Start the VM:

xl create vm1.cfg

Managing DomUs with xl

Start a VM from configuration:

xl create vm1.cfg

List running VMs:

xl list

Expected output:

Name                   ID     Mem   VCPUs   State   Time(s)
Domain-0               0     2048     8    r-----   134.2
vm1                   10     1536     2    -b----     5.4
vm2                   11     1536     2    -b----     5.1

Connect to VM console:

xl console vm1

Graceful shutdown:

xl shutdown vm1

Force shutdown:

xl destroy vm1

Reboot:

xl reboot vm1

Get resource usage:

xl top

Pause a VM (useful for snapshots):

xl pause vm1

Resume a paused VM:

xl unpause vm1

Check VM details:

xl dominfo vm1

Duplicating VMs

Once a DomU is configured, duplication is straightforward:

cp vmdisk0 vmdisk1
cp vm1.cfg vm2.cfg

Edit vm2.cfg to change the name and any other parameters:

name = "vm2"
disk = [ 'file:/home/xen/vmdisk1,xvda,w' ]

Start the new VM:

xl create vm2.cfg

Persistent VM Auto-Start

To have VMs start automatically on Dom0 boot, place their configuration files in /etc/xen/auto/:

cp vm1.cfg /etc/xen/auto/vm1.cfg

The Xen toolstack will create them during startup.

Modern Alternatives

For new deployments, consider:

KVM with libvirt: Standard on most Linux distributions, better tooling ecosystem
Containers: Docker/Podman for applications that don’t need full VMs
Cloud-native solutions: Kubernetes for orchestration if managing multiple machines

If you’re maintaining existing Xen infrastructure, xl provides all necessary management. Avoid xm—it’s unmaintained and missing features in current Xen versions.