Using xl
xl is a minimalistic CLI tool to interact with the hypervisor. The xl man page, distributed alongside the tool itself, is the current authoritative documentation about its interface.
If you haven’t used xl before, keep reading through the Getting Started page, as it provides a practical introduction.
If you’ve used it before and would like to learn more practical examples, jump over Configuration file. It shows more options than the introductory material, and provides links to the authoritative documentation of the configuration files.
If you’d rather see a collection of examples instead then head over Examples. This is a set of typical use cases along with known caveats and fairly straightforward instructions.
Note
The Xen Project has deprecated various configuration options on paper, while still being supported in code. Many online tutorials still use now obsolete syntax, so bear in mind that in case of confusion the man pages are the authoritative source of truth.
Getting started
Interactions with the hypervisor are privileged, so the alternatives to use xl are to run as root, or prepend sudo to every command. Choose whatever is typical in your OS. These instructions assume a working graphical interface in dom0.
First of all, make sure the tool works. The following command outputs hypervisor information; This includes Xen version, command line arguments, etc.
xl info
If the output is a few lines with Permission denid at the end, then either you’re not running under Xen, you’re not running as root, or you’re not running with sudo.
With that check done, create your first guest. Create a folder for it (say, /path/to/myguest/). Download the installer ISO for the guest in the folder as installer.iso. Then, create a virtual hard disk for your guest. xl supports a number of formats, but to keep things simple, use qemu-img to create a resizable 10GiB root disk.
qemu-img create -f qcow2 disk.qcow2 10G
And create a new file in that same folder called myguest.cfg with the following contents.
name = 'my_favourite_guest'
type = 'hvm'
memory = 2048
vcpus = 2
serial = 'pty'
disk = ['format=raw, vdev=xvda, access=w, target=disk.qcow2',
'format=raw, vdev=xvdb, access=r, devtype=cdrom, target=installer.iso']
Finally, execute the following xl command to start a new guest.
xl create myguest.cfg
The list of running guests can be queried through yet another xl command, so use it to ensure the guest is actually running.
xl list
Warning
If at any point later on something goes wrong and you want to kill the guest,
you can use xl destroy my_favourite_guest. Forceful termination of a
guest is highly dangerous as its the VM equivalent of pulling the plug of a
physical machine; the same data corruption considerations apply. You
typically want to ask the guest itself to turn itself off if at all possible.
After you get a display, go through the installer as you typically would. Internet should work as long as dom0 is itself connected. After the final installation step, turn the VM off as we need to remove the ISO from the cfg file. Afterwards, it should look like so:
name = 'my_favourite_guest'
type = 'hvm'
memory = 512
vcpus = 2
vif = ['bridge=xenbr0']
disk = ['format=raw, vdev=xvda, access=w, target=disk.qcow2']
Create the guest again with xl create, which will now boot into the root disk as a real machine would.
Configuration file
The most important step for guest creation is setting up an appropriate .cfg file. Getting started showed a few basic keys, but there’s a lot more. The xl.cfg man page contains up-to-date documentation on the format of the file and all available keys.
Note
The contents of the disk and vif keys are further described in the xl disk configuration man page and the xl networking configuration man page respectively.
Typical choices are:
Guest type: PV or HVM
Firmware (HVM-only): SeaBIOS, RomBIOS or OVMF
Bootloader (PV-only): Direct boot, pvgrub2 or pygrub
Advanced usage
TODO
Configuring virtual storage
TODO
Configuring networking
TODO