Installing Xen on Fedora 17 as Domain-0

Xen remains relevant for certain production workloads, particularly in cloud infrastructure (AWS EC2, Citrix Hypervisor) and enterprise environments requiring strong VM isolation. However, most Linux distributions now default to KVM for virtualization due to simpler setup and broader ecosystem support. If you’re evaluating hypervisors, consider KVM or container-based solutions like Podman and Kubernetes for new deployments.

This guide covers setting up Xen Domain-0 on modern Fedora (tested on Fedora 41+). The process is significantly simpler than early Xen setups, which required manual kernel patching and compilation. Current Fedora and upstream Linux kernels include native Xen support via PV ops technology.

Installation

Install Xen and dependencies:

dnf install xen xen-libs xen-devel

On Fedora 41+, the standard Linux kernel includes Domain-0 support. The toolstack has transitioned from the legacy xm/xend to xl, which is faster and more reliable.

Configure the Boot Entry

After installation, regenerate the GRUB2 configuration to ensure Xen appears as a boot option:

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

Enable and start the Xen daemon:

systemctl enable xen
systemctl start xen

Reboot and select the Xen entry from the GRUB2 menu. After booting into Domain-0, verify the installation:

xl info

You should see output similar to:

host                   : myhost.example.com
release                : 6.8.0-1.fc41.x86_64
version                : #1 SMP Mon Jan 13 12:34:56 UTC 2025
machine                : x86_64
nr_cpus                : 8
nr_nodes               : 1
cores_per_socket       : 4
threads_per_core       : 2
cpu_mhz                : 3400
total_memory           : 16384
free_memory            : 8192
xen_major              : 4
xen_minor              : 18
virt_caps              : hvm
xen_scheduler          : credit2

Network Configuration

Network setup is manual and varies by Fedora version and your environment. The legacy NetworkManager integration with Xen is unreliable, so we configure bridges directly.

Using Traditional Bridge Networking

Stop and disable NetworkManager:

systemctl disable NetworkManager
systemctl mask NetworkManager
systemctl restart networking

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

DEVICE=xenbr0
TYPE=Bridge
ONBOOT=yes
DELAY=0
BOOTPROTO=dhcp
IPV6INIT=no

Edit the physical interface configuration (e.g., /etc/sysconfig/network-scripts/ifcfg-eno1), replacing it with:

DEVICE=eno1
TYPE=Ethernet
ONBOOT=yes
BRIDGE=xenbr0
NM_CONTROLLED=no

Apply the changes:

systemctl restart networking

Verify the bridge:

ip link show
ip addr show xenbr0

Using Netplan (Alternative)

On systems using Netplan (some Fedora spins), create /etc/netplan/01-xen-bridge.yaml:

network:
  version: 2
  ethernets:
    eno1:
      dhcp4: false
  bridges:
    xenbr0:
      interfaces: [eno1]
      dhcp4: true

Apply with:

netplan apply

Private Network with Dummy Device

For laptops with only wireless connectivity, create a dummy bridge:

#!/bin/bash
# Create dummy bridge for isolated VM network

modprobe dummy
ip link add xenbr0 type bridge
ip link set xenbr0 up
ip addr add 10.0.0.2/16 dev xenbr0

# Enable NAT and forwarding
iptables -I FORWARD -j ACCEPT
iptables -t nat -I POSTROUTING -o wlan0 -j MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward

Save as /usr/local/bin/xen-bridge-setup.sh and make executable:

chmod +x /usr/local/bin/xen-bridge-setup.sh

Create a systemd service to run at boot. Create /etc/systemd/system/xen-bridge.service:

[Unit]
Description=Xen Bridge Setup
After=network-online.target
Wants=network-online.target

[Service]
Type=oneshot
ExecStart=/usr/local/bin/xen-bridge-setup.sh
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Enable it:

systemctl daemon-reload
systemctl enable xen-bridge
systemctl start xen-bridge

Creating a Domain-U Configuration

Create a VM configuration file at /etc/xen/vm-example.cfg:

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

Key options:

• disk: Use phy: for LVM volumes or raw partitions, file: for image files
• vif: Defines virtual network interfaces; bridge=xenbr0 attaches to the bridge
• bootloader: Use pygrub for PV guests with a bootable kernel, or hvmloader for HVM guests
• vcpus and memory: CPU and RAM allocation

Create the LVM volume first:

lvcreate -L 20G -n vm-example-root /dev/vg_xen

Start the VM:

xl create /etc/xen/vm-example.cfg
xl list

Common xl Commands

• xl create <config> — Create and start a domain
• xl console <domain> — Attach to serial console
• xl shutdown <domain> — Graceful shutdown
• xl destroy <domain> — Force shutdown
• xl reboot <domain> — Reboot domain
• xl save <domain> <file> — Suspend to disk
• xl restore <file> — Resume from disk
• xl vcpu-set <domain> <count> — Adjust vCPUs (if supported)
• xl mem-set <domain> <MB> — Adjust memory (if supported)

Most operations replace the legacy xm command directly.

Troubleshooting

Domain fails to boot: Check /var/log/xen/ for hypervisor messages. Ensure the kernel is Domain-0 compatible.

Bridge not working: Verify with brctl show and iptables -t filter -L FORWARD if NAT is required.

Console access denied: Use xl console <domain> and ensure the serial console is configured in the guest kernel parameters.

Memory pressure: Monitor with xl info and free -h. Overallocation without ballooning causes performance degradation.