Getting started

Choose a base OS

You can install the Xen hypervisor in a number of base OSs, including numerous Linux distributions and some BSD flavours. Typical choices are AlpineLinux, Debian or FreeBSD; but you can use many others.

Note

An easy rule of thumb is to check your base OS documentation on whether it supports running as a Xen dom0 (not to be confused with a Xen domU).

Attention

To support HVM guests, ensure that virtualization extensions are enabled in the BIOS. If your system does not support these extensions, you will be unable to use the hypervisor to virtualize unmodified OS systems. However, paravirtualization will work just well.

The virtualization choices varies between BIOS releases, but are commonly referred to as “Enable Intel VT” for Intel chipsets, “Enable AMD-V” for AMD, or simply “Enable Virtualization Technology”.

Install the required packages

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First, make sure your Debian system is up to date:

sudo apt-get update && sudo apt-get upgrade

Then, install the Xen project software:

sudo apt-get install xen-system-amd64

Reference link: Click here!

First, activate the Alpine community repository (check this wiki page for more information), then install Xen and the seabios (BIOS) and ovmf (UEFI) firmwares for its virtual machines.

apk add xen xen-hypervisor seabios ovmf

This will install Xen Hypervisor, the xl cli tool, and all necessary packages. The following step is to load the essential kernel modules for Xen. We will add them to /etc/modules, so they will be loaded automatically at boot:

echo "xen-netback" >> /etc/modules
echo "xen-blkback" >> /etc/modules
echo "tun" >> /etc/modules

Lastly, we set the default runlevel to include the Xen daemons.

rc-update add xenconsoled
rc-update add xendomains
rc-update add xenqemu
rc-update add xenstored

Reference link: Click here!

Xen Dom0 Package Installation

pkg install -y xen-kernel xen-tools

Configure your bootloader

After the installation process, Xen needs to be configured for it to boot. Open /etc/default/grub (or /etc/default/grub.d/xen.cfg) and look for a variable called GRUB_CMDLINE_XEN_DEFAULT. If the variable isn’t set, allocate enough memory and cpu’s for it to run properly using the following syntax:

GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=2G,max:2G dom0_max_vcpus=4"

  • dom0_mem,max sets the memory available to dom0

  • dom0_max_vcpus to limit the number of vCPUs allocated for dom0

Then apply the changes and reboot as follows:

sudo update-grub
sudo reboot

If the system doesn’t boot properly (for example it freezes everytime), that might mean that not enough recources were allocated to the system. Try to play around with the values until the system works smoothly.

Once running a Xen kernel, you will have to change its command-line arguments and activate the default GRUB entry by writing this at the bottom of /etc/default/grub:

# You need to set the amount of RAM to allocate to the Dom0 Alpine install so that
# our future virtual machines will have enough memory.
GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=1024M,max:1024M"

GRUB_DEFAULT="saved"
GRUB_SAVEDEFAULT="true"

Replace 1024M with the amount of memory you want to dedicate to your dom0 operating system. After that, execute the following command:

grub-mkconfig -o /boot/grub/grub.cfg
grub-set-default "$(grep ^menuentry /boot/grub/grub.cfg | grep Xen | cut -d \' -f 2 | head -1)"

Note

This changes the default entry in GRUB to the first one containing ‘Xen’. Run this each time you upgrade Alpine or Xen.

After the installation was successful, follow the instructions given at the end of the packages which will say to modify /etc/sysctl.conf, /etc/ttys and /boot/loader.conf.

Also, Xen will require to add the following lines into /etc/rc.conf:

cloned_interfaces="bridge0"
ifconfig_bridge0="addm <primary network interface i.e. igb0> up"

Finally, reboot the host to boot to the Xen kernel.

Note

You should see the Xen kernel output and the FreeBSD kernel output. It is important to be aware of the dom0_mem and dom0_max_vcpus parameters in /boot/loader.conf, especially on root-on-ZFS systems with ZFS ARC read caching.

Post-install checks

Your next boot should start a Xen system. Verify this is the case by running xl info on your terminal, which ought to print hypervisor details into your screen.

Warning

xl is a low-level CLI tool to communicate with the Xen hypervisor and requires you to run it with sudo or as root. Otherwise, the tool can’t operate.

Attention

If the xl command doesn’t work by saying that no hypervisor was found, it means that the system hasn’t booted with the hypervisor. If that’s the case, double check you’re selecting the appropriate menuentry when booting. A common mistake is having a GRUB_TIMEOUT=0 and the wrong GRUB_DEFAULT. Check this page for more information on these options. Note that you can usually force the GRUB menu to appear (even when it’s normally hidden) by holding SHIFT during early boot.

Next steps

You need to set up a suitable toolstack to create/list/destroy your domains.

If you’re just playing around the easiest way to start creating them is through the xl tool that you’ve installed as part of this section. See Using xl to learn how to use it.

Head over the Administration page instead if you need a specialised administration setup.