Using and Understanding

Xen4CentOS Russell Pavlicek, Xen Project

Evangelist

A summary of the Xen4CentOS

project, use, and status

First thing…

A personal word of appreciation to the CentOS

team

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

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

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

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

That’s About All It Takes

Really…

It’s about that simple.

It’s not hard.

And it’s not rocket science.

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!

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

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

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”

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

Getting Help

• IRC:

• #centos-virt irc channel on irc.freenode.net

• Mailing List:

• centos-virt list on lists.centos.org

The Future

• Original intent of updating Xen4CentOS for

every other release

• Increased supportability using regular CentOS

and Xen Project communities

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.

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

Questions?

Russell.Pavlicek@XenProject.org

@RCPavlicek