Installing and Configuring Xen Hypervisor on Fedora

Xen remains a production-grade hypervisor used by major cloud providers like AWS and Citrix, though KVM has become the default for most Linux distributions. This guide covers setting up Xen Domain-0 (the privileged management domain) on modern Fedora systems.

Installing Xen Packages

Install the required Xen packages:

sudo dnf install xen xen-libs xen-runtime xen-dom0-tools

Modern Fedora kernels include pv_ops support required for Domain-0 operation, so no kernel patching is necessary. The xen-dom0-tools package provides essential management utilities like xl and xm.

Verify the installation:

rpm -qa | grep xen

Configuring the Boot Loader

Update GRUB2 to include the Xen hypervisor entry:

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

On UEFI systems, use:

sudo grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg

Reboot and select the “Xen” entry from the GRUB2 boot menu. To set it as the default, edit /etc/default/grub:

GRUB_DEFAULT='Fedora (Xen hypervisor)'

Then regenerate the configuration:

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

After booting into Domain-0, verify Xen is functioning:

xl info

This displays system information including Xen version, CPU count, memory allocation, and capabilities. A successful output confirms Domain-0 is operational.

Setting Up Network Bridging for Guests

Xen guests require a bridge for network connectivity. Modern Fedora systems use systemd-networkd or NetworkManager, depending on your setup. If NetworkManager is active and you prefer traditional network management:

sudo systemctl disable NetworkManager.service
sudo systemctl enable network.service
sudo systemctl start network.service

Using systemd-networkd (Recommended for Modern Fedora)

Create a netdev file for the bridge /etc/systemd/network/xenbr0.netdev:

[NetDev]
Name=xenbr0
Kind=bridge

Create a network configuration /etc/systemd/network/xenbr0.network for DHCP:

[Match]
Name=xenbr0

[Network]
DHCP=ipv4

Or for static IP:

[Match]
Name=xenbr0

[Network]
Address=192.168.1.50/24
Gateway=192.168.1.1
DNS=8.8.8.8

Create a configuration for your physical interface /etc/systemd/network/enp0s25.network:

[Match]
Name=enp0s25

[Network]
Bridge=xenbr0

Apply the changes:

sudo systemctl restart systemd-networkd

Using Traditional Network Scripts

Create /etc/sysconfig/network-scripts/ifcfg-xenbr0 for DHCP:

DEVICE=xenbr0
TYPE=Bridge
ONBOOT=yes
DELAY=0
BOOTPROTO=dhcp

Or for static IP:

DEVICE=xenbr0
TYPE=Bridge
ONBOOT=yes
DELAY=0
BOOTPROTO=static
IPADDR=192.168.1.50
NETMASK=255.255.255.0
GATEWAY=192.168.1.1

Edit your physical network adapter’s configuration (e.g., /etc/sysconfig/network-scripts/ifcfg-enp0s25):

BRIDGE=xenbr0

Restart the network service:

sudo systemctl restart network.service

Verify Bridge Setup

Verify the bridge is operational:

ip addr show xenbr0
bridge link show

You should see the physical interface as a member of the bridge.

Creating Guest Storage

Create an LVM logical volume for the guest:

sudo lvcreate -L 20G -n vm-guest1 vg_xen

Or create a file-based disk image:

sudo truncate -s 20G /var/lib/xen/images/guest1.img

Creating a Domain-U (Guest) Configuration

Create a guest configuration file at /etc/xen/vm-guest1.cfg:

name = "guest1"
vcpus = 2
memory = 2048
disk = [ 'phy:/dev/vg_xen/vm-guest1,xvda,w' ]
vif = [ 'bridge=xenbr0' ]
bootloader = "/usr/bin/pygrub"
on_reboot = "restart"
on_crash = "restart"

Configuration options:

• name: Guest domain identifier
• vcpus: Virtual CPU count
• memory: RAM in MB
• disk: Block device mapping (phy: for physical volumes, file: for image files)
• vif: Virtual interface configuration with bridge binding
• bootloader: Use pygrub for PV guests or omit for HVM guests with direct kernel boot
• on_reboot/on_crash: Behavior policies

For file-based disk images:

disk = [ 'file:/var/lib/xen/images/guest1.img,xvda,w' ]

For HVM guests with UEFI:

name = "guest1-hvm"
type = "hvm"
vcpus = 4
memory = 4096
disk = [ 'file:/var/lib/xen/images/guest1-hvm.img,hda,w' ]
vif = [ 'bridge=xenbr0' ]
kernel = "/usr/lib/xen/boot/hvmloader"
bios = "ovmf"

Managing Guest Domains

Start a guest:

xl create /etc/xen/vm-guest1.cfg

List running domains:

xl list

Get detailed domain information:

xl dominfo guest1

Connect to guest console:

xl console guest1

Exit the console with Ctrl+].

Pause and unpause a guest:

xl pause guest1
xl unpause guest1

Destroy a guest:

xl destroy guest1

Create a persistent guest that doesn’t auto-start:

xl create -p /etc/xen/vm-guest1.cfg

The -p flag prevents immediate startup, allowing manual management.

Monitoring and Troubleshooting

Check Xen daemon status:

sudo systemctl status xen.service

View Xen logs in real-time:

journalctl -u xen -f

Monitor resource usage across domains:

xl top

Check domain-specific statistics:

xl stats guest1

Network Connectivity Issues

Verify bridge membership:

bridge link show
ip link show

Ensure guest vif devices are properly attached to the bridge. Check for the guest’s vif peer on the host:

ip link show | grep vif

If a guest loses network connectivity, verify the vif is active:

xl vif-list guest1

Reconnect a vif if needed:

xl network-detach guest1 0
xl network-attach guest1 bridge=xenbr0

Console Access Issues

If console access fails, check if xenstored is running:

sudo systemctl status xenstored

Restart Xen services if needed:

sudo systemctl restart xen.service

Enabling Domain-0 Autostart

To automatically start registered guests on boot, enable the service:

sudo systemctl enable xen.service
sudo systemctl enable xendomains.service

Guests created with persistent configurations will auto-start. To disable autostart for a specific guest:

xl shutdown guest1
xl destroy guest1

Then recreate it without -p if you want it to auto-start, or with -p if you manage it manually.