Xen Dom0 on USB or SD

2017-10-23T15:49:01Z

Richtrabing: Updating syslinux configuration with new kernel, initrd and modloop filenames; some changes to setting up apk repos and some of the notes on edge cases.

This guide will show you how to perform a Xen Dom0 install on a USB or SD card, so you can have your Dom0 running from tmpfs. This has some benefits, but you will need a place to store your guests (virtual machines) and a syslog server to redirect the logs to.

The first step is to set up a basic usb or SD install, to do this boot from the Alpine install CD (minimal is fine) and follow one of the following guides: [[Create a Bootable USB]] or [[Create a Bootable Compact Flash]].

Once you finished installing Alpine Linux on your device, boot from it and configure your newly installed system:

Setup the network interfaces and apk repositories:

<pre>
# setup-interfaces
# setup-apkrepos
[...]
# apk update
</pre>

{{Note| you may need to edit /etc/apk/repositories and change the first line so it points to /media/usb/apks.}}

Now that you have your system properly configured, it's time to install Xen:

<pre>
# Should this not be apk add xen xen-hypervisor ?
# apk add xen
</pre>

Now we have Xen installed, but we will need to modify the usb [[Bootloaders|bootloader]] in order to load the Xen kernel. The first step is to remount /media/usb with write permissions:

<pre>
# mount -o remount,rw /media/usb
</pre>

Then, copy the Xen kernel and mboot.c32 to the usb boot partition:

<pre>
# cp /boot/xen.gz /media/usb/boot/
# cp /boot/mboot.c32 /media/usb/boot/
</pre>

Now we have all the necessary files to boot Xen from the usb, it's time to change the bootloader and add a Xen entry, to do so open /media/usb/syslinux.cfg with your favorite editor and add one of the following entries:

Normal boot:
<pre>
LABEL xen
KERNEL /boot/mboot.c32
APPEND /boot/xen.gz --- /boot/vmlinuz-hardened alpine_dev=usbdisk:vfat modules=loop,squashfs,sd-mod,usb-storage modloop=/boot/modloop-hardened --- /boot/initramfs-hardened
</pre>

{{Note|<nowiki>you might have to use alpine_dev=UUID=XXXX-XXXX:vfat might work as well. UUID can be read using blkid.</nowiki>}}
{{Note|<nowiki>alternatively, using /media/UUID=XXX-XXXX instead of /media/usb, see /proc/mounts to detected where is your usb/cf card mounted.</nowiki>}}

Serial console boot:
<pre>
LABEL xen
KERNEL /boot/mboot.c32
APPEND /boot/xen.gz com1=115200,8n1 console=com1 --- /boot/vmlinuz-hardened alpine_dev=usbdisk:vfat modules=loop,squashfs,sd-mod,usb-storage modloop=/boot/modloop-hardened --- /boot/initramfs-hardened
</pre>

Change the UUID to the correct one, and add the necessary modules for your system. It's also a good idea to check [http://wiki.xen.org/wiki/Xen_Hypervisor_Boot_Options Xen Boot options] and set dom0_mem, dom0_vcpus_pin and dom0_max_vcpus at least.

The next step is to load the necessary kernel modules for Xen, we will add them to /etc/modules, so they will be loaded automatically on boot:

<pre>
# echo "xen_netback" >> /etc/modules
# echo "xen_blkback" >> /etc/modules
# echo "tun" >> /etc/modules
</pre>

The last step is to configure startup services, we will need udev and xencommons at least to be started on boot:

<pre>
# rc-update add udev sysinit
# rc-update add udev-postmount
# rc-update add xenstored
# rc-update add xenconsoled
</pre>

Ok, now you have a fully functional Xen install, it's time to save your changes and boot into it.

<pre>
# lbu commit
# reboot
</pre>

Also remember to configure at least one network bridge following the [[Bridge]] guide.

== See also ==
* [[Xen Dom0]]

[[Category:Virtualization]]

Alpine Linux - User contributions [en]

Xen Dom0 on USB or SD