Xen Dom0 on USB or SD
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:
# setup-interfaces # setup-apkrepos [...] # apk update
Now that you have your system properly configured, it's time to install Xen:
# Should this not be apk add xen xen-hypervisor ? # apk add xen
Now we have Xen installed, but we will need to modify the usb bootloader in order to load the Xen kernel. The first step is to remount /media/usb with write permissions:
# mount -o remount,rw /media/usb
Then, copy the Xen kernel and mboot.c32 to the usb boot partition:
# cp /boot/xen.gz /media/usb/boot/ # cp /boot/mboot.c32 /media/usb/boot/
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:
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
Serial console boot:
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
Change the UUID to the correct one, and add the necessary modules for your system. It's also a good idea to check 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:
# echo "xen_netback" >> /etc/modules # echo "xen_blkback" >> /etc/modules # echo "tun" >> /etc/modules
The last step is to configure startup services, we will need udev and xencommons at least to be started on boot:
# rc-update add udev sysinit # rc-update add udev-postmount # rc-update add xenstored # rc-update add xenconsoled
Ok, now you have a fully functional Xen install, it's time to save your changes and boot into it.
# lbu commit # reboot
Also remember to configure at least one network bridge following the Bridge guide.