Delivered by Russell Pavlicek at CentOS Dojo, Denver, CO, April 10. 2014. A basic introduction to Xen4CentOS: What it provides, how to install it, and where it is going.

1. Using and Understanding
Xen4CentOS
Russell Pavlicek, Xen Project
Evangelist
A summary of the Xen4CentOS
project, use, and status

2. First thing…
A personal word of appreciation to the CentOS
team

3. The Problem
• Red Hat made a business decision to focus on KVM
• In RHEL 6, they disabled support for the Xen Project
Control Domain (aka Dom0) in their kernel
• Many Xen Project users on CentOS 5 users want to
upgrade to CentOS 6, but don’t want to change
hypervisors and tools to accomplish it
• So there is a need to reintroduce a Xen Project
hypervisor option in CentOS 6

4. What Xen4CentOS Provides
• Xen Project 4.2.x
• Linux Kernel 3.10.x (kernel.org LTS kernel)
• blktap 2.5 userspace tools
• https://github.com/xen-org/blktap
• blktap 2.5 drivers in the Centos6 Xen 3.4.x
dom0 kernel
• libvirt 0.10.x with drivers for both xm/xend and
xl/libxl toolstacks

5. Quicky HOWTO
• Start with a minimal CentOS installation
• Include the usual Xen Project considerations (LVM,
etc.)
• Set up the installation repository:
• yum install centos-release-xen
• Install the software:
• yum install xen
• Install the grub boot entries:
• /usr/bin/grub-bootxen.sh

6. Quicky Checkout
• Check /boot/grub/grub.conf for entry like:
title CentOS (3.10.34-11.el6.centos.alt.x86_64)
root (hd0,0)
kernel /xen.gz dom0_mem=1024M,max:1024M loglvl=all guest_loglvl=all
module /vmlinuz-3.10.34-11.el6.centos.alt.x86_64 ro root=/dev/mapper/vg_xen01-lv_root
rd_LVM_LV=vg_xen01/lv_swap rd_NO_LUKS KEYBOARDTYPE=pc KEYTABLE=uk
rd_NO_MD LANG=en_GB rd_LVM_LV=vg_xen01/lv_root SYSFONT=latarcyrheb-sun16
crashkernel=auto rd_NO_DM rhgb quiet
module /initramfs-3.10.34-11.el6.centos.alt.x86_64.img
• Reboot and do:
• uname -r ; xm info

7. That’s About All It Takes
Really…
It’s about that simple.
It’s not hard.
And it’s not rocket science.

8. Issues and Limitations
• SELinux support is disabled
• You might need to disable SELinux on the dom0 for
some operations; primarily when using qemu-xen
and blktap backed storage.
• For the time being, only Xen4CentOS on
CentOS-6/x86_64 is available.
• 32 bit may eventually be added, if there is enough
demand
• If you need it, speak up and join in!

9. Issues and Limitations (continued)
• Serial Console
• Must be setup manually if you intend to re-route the
dom0 console as well
• libvirt and xl/xm compatibility
• Both xl and xm are supported and tested on
command line
• Currently, libvirt is only completely functional with
xm (which needs xend running); native xl support in
libvirt is expected in a future release

10. Issues and Limitations (continued)
• Ballooning
• A bug in Linux's balloon driver can be worked
around with a Xen Project command line option;
see CentOS bug 6893 report
• No UEFI support
• Xen Project hypervisor 4.2 does have UEFI
support, but the Linux 3.4 dom0 kernel doesn't have
UEFI support yet
• Thus, Secure Boot is unsupported

11. Issues and Limitations (continued)
• The Xen4CentOS LTS kernel is not the Red Hat
kernel
• If you rely on Red Hat-specific modifications to your
kernel, you won’t find them here
• But the focus of this kernel is to run the Control
Domain (Dom0) only; the work normally assigned to
Dom0 is primarily control of the hypervisor, which
should not require any “special sauce”

12. References and Resources
• Release notes:
• http://wiki.centos.org/Manuals/ReleaseNotes/Xen4-01
• Wiki:
• http://wiki.centos.org/QaWiki/Xen4
• QuickStart:
• http://wiki.centos.org/HowTos/Xen/Xen4QuickStart
• History and Motivations Video, by Karanbir
Singh:
• https://www.youtube.com/watch?v=DtXjnGdgIZ0

13. Getting Help
• IRC:
• #centos-virt irc channel on irc.freenode.net
• Mailing List:
• centos-virt list on lists.centos.org

14. The Future
• Original intent of updating Xen4CentOS for
every other release
• Increased supportability using regular CentOS
and Xen Project communities

15. The Future (continued)
• The CentOS Virtualization SIG (March 5, 2014)
• http://wiki.centos.org/SpecialInterestGroup/Virtualization
• “The Virt-SIG aims to deliver a user consumable full stack for
virtualization technologies that want to work with the SIG. This
includes delivery, deployment, management, update and patch
application ( for full lifecycle management ) of the baseline platform
when deployed in sync with a technology curated by the Virt-SIG.”
• “The CentOS Virt-SIG wants to build upon the already successfully
released Xen4CentOS project. Moving forward the Xen4CentOS
codebase will be shifted over to the Virt-SIG resources.”
• Interest regarding other virtualization technologies like
OpenVZ, KVM, etc.

16. Upcoming Meetings
• If you use or hack Xen4CentOS, consider attending or
speaking at one of these upcoming meetings:
• Xen Project Developer Summit
• Co-located with LinuxCon NA, Chicago IL, Aug 18-19
• CFP is open until May 2
• Xen Project Users Summit
• New York City, Sept 15
• CFP is open until May 31
• The perfect time for a long weekend in Manhattan!
• Check out http://xenproject.org/about/events.html

17. Questions?
Russell.Pavlicek@XenProject.org
@RCPavlicek