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Fernando Rodrigues a24d666578

This very basic documentation page contains a small introduction to Xen taken from my previous writeup at the NixOS Wiki, and some instructions on how to import the domU profile and enable Dom0.

Signed-off-by: Fernando Rodrigues <alpha@sigmasquadron.net>

2026-02-03 14:59:03 +11:00

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Xen Project Hypervisor

Introduction

The Xen Project Hypervisor is an open-source type-1 virtual machine manager which allows multiple virtual machines, known as domains, to run concurrently with the host on the physical machine. This is unlike a typical type-2 hypervisor, such as QEMU, where the virtual machines run as applications on top of the host. NixOS runs as the privileged Domain 0, and can paravirtualise (PV Mode) or fully virtualise (HVM Mode) unprivileged domains (domUs).

Xen is security-supported in NixOS. All Xen Security Advisories are patched within hours of release, and generally reach the binary cache channels within a couple of days.

Domain 0 Installation

Xen may be used as a Domain 0 since NixOS 24.11, using the {option}virtualisation.xen.enable option. There are various hardware and software requirements to running a Xen Domain 0; the module is configured to prevent running Xen on a NixOS system that does not meet the software requirements. (i.e. a NixOS system that uses the legacy, scripted initial ramdisk.) The module does not yet check if the hardware requirements are met: please manually ensure that the target machine supports SLAT and IOMMU, the latter being required only for non-PV domains to be virtualised.

The boot menu on a Xen-enabled NixOS system will show duplicate entries for each generation: one boots a normal NixOS system, and the other boots into the Xen Project Hypervisor. The systemd-boot and Limine bootloaders are the only supported boot methods at this time.

Xen may be managed through various frontend configuration systems. libxenlight is one such configuration system, and is built into all Xen systems. The xl command is the primary command-line interface to libxenlight, and is capable of managing a NixOS Domain 0.

Unprivileged Domain Installation

Known generically as guests, unprivileged domains running NixOS may import the xen-domU.nix profile in their configurations to automatically enable various recommended optimisations which are relevant for unprivileged domains.

:::{.example}

Import the Xen Unprivileged Domain profile into a NixOS configuration

{
  imports = [
    <nixpkgs/nixos/modules/virtualisation/xen-domU.nix>
  ];
}

:::

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