Xen on Linux

A Young Hacker's Illustrated Primer

Austin Godber

godber@uberhip.com

JumpBox, Inc.

Xen Virtualization

• Paravirtualization
  • Modified Guest
  • Application code remains unmodified
  • Slightly improved performance over full virtualization
  • No dynamically scanning code for pitfalls required
• Hardware Assisted Full Virtualization
• Recent x86 hardware

  egrep "vmx|svm" /proc/cpuinfo

• Unmodified Guest
• Still no need to dynamically scan code for pitfalls

Paravirtualization

Paravirtualization - Xen Style

Xen on Ubuntu 7.04

These instructions mainly come from the Ubuntu Wiki Xen Page. I will assume paravirt x86.

• Installing Xen is effortless

  sudo aptitude install ubuntu-xen-desktop
  sudo reboot

• What do we have after reboot?

  sudo xm list

• Now configure Xend to used bridge networking, add (network-script network-bridge) to /etc/xen/xend-config.sxp and restart xend

  sudo xend stop
  sudo xend start
  

Xen on Ubuntu 7.04 (cont.)

Now you have your Dom0 up and xend configured. Its time to make a DomU. We have block device choices to make.

• Loopback stands for lazy, so thats what we will do!

  sudo dd if=/dev/zero of=/usr/local/edgy.ext3 \
       bs=1024k seek=4096 count=0
  sudo mkfs.ext3 /usr/local/edgy.ext3
  sudo mkdir /mnt/edgy
  sudo mount /usr/local/edgy.ext3 /mnt/edgy -o loop
  sudo apt-get install debootstrap
  sudo debootstrap edgy /mnt/edgy
  

Xen on Ubuntu 7.04 (cont.)

While the Guest's disk is still loopback mounted lets tweak some things:

• Network settings, remember, we bridged it and I am assuming my LAN has DHCP, so /mnt/edgy/etc/network/interfaces should contain:

   auto lo
   iface lo inet loopback
  
   auto eth0
   iface eth0 inet dhcp 

• Now we set up your fstab at /mnt/edgy/etc/fstab

  proc            /proc           proc    defaults        0       0
  /dev/hda1       /               ext3    defaults,errors=remount-ro 0       1
  

Xen on Ubuntu 7.04 (cont.)

While the Guest's disk is still loopback mounted lets tweak some things:

• Set your hostname in /mnt/edgy/etc/hostname

  edgyvm

• Set your hostname in /mnt/edgy/etc/hosts

  127.0.0.1       localhost
  127.0.1.1       edgyvm
  	

• The loopback fun is over, time to unmount:

  sudo umount /mnt/edgy
  	 

Xen on Ubuntu 7.04 (cont.)

The previous slide was pretty boring, so lets edit the Xen config file.

• Edit /etc/xen/edgy-guest.cfg with your favorite editor:

   kernel = "/boot/vmlinuz-2.6.19-4-generic"
   ramdisk = "/boot/initrd.img-2.6.19-4-generic"
   builder='linux'
   memory = 128
   name = "edgy-guest"
   vcpus = 1
   vif = [ 'bridge=xenbr0' ]
   disk = [ 'file:/usr/local/edgy.ext3,ioemu:hda1,w' ]
   root = "/dev/hda1 ro"
  	

Xen on Ubuntu 7.04 (cont.)

Now we are ready to boot our first DomU.

• Boot up the new guest:

  sudo xm create edgy-guest.cfg

• What do we have??

  sudo xm list

• Get a console on that guest:

  sudo xm console edgy-guest

• Trapped? Escape with this!:

  CTRL+]

Xen Misc and Troubleshooting

• What about HVM?
• Trouble?
• xm help
• sudo xm dmesg
• sudo xm info
• sudo xm network-list
• States shown in sudo xm list:
  running, blocked, paused,
  shutdown, crashed, dying
• Logs in /var/log/xen/

Xen Bonuses

• Enomolism - Web UI
• ConVirt/Xenman - Desktop UI Manager
• Ganeti - CLI Cluster Manager
• xen-tools - CLI tools
• HyperVM - Commercial Web UI
• virt-manager - RedHat's Desktop UI Manager
• Others...

References

Since Xen started off as an academic research project at University of Cambridge, there is a large body of academic papers on its design and performance.

• Xen and the Art of Virtualization [mirror]
• Xen and the Art of Repeated Research [mirror]
• Xen 3.0 Users Manual [mirror]
• Live Migration of Virtual Machines [mirror]
• Dell's Overview of Xen [mirror]

Attribution

This presentation was prepared using S5: A Simple Standards-Based Slide Show System in Gvim on Ubuntu 7.04 or in Textmate on a Mac.