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Testing out the Xen live CD

Linux had always lacked a open source virtualization technology in the same league as Solaris Containers or a commercial product like VMware. That was until Xen came into the picture. Xen is an open source virtual machine monitor for x86 that supports execution of multiple guest operating systems. Xen is released under the GPL and can easily be used to run operating systems as diverse as different Linux distributions, BSDs and even Windows XP (though Windows port is not available because of licensing restrictions).

Virtualization technologies are nothing new, what with VMware, User-mode Linux and others available. But Xen is relevant here because of the support for it from Red Hat, its GPL license, and also its active development. Strictly speaking, Xen does not do full virtualization like that being done by commercial ventures like VMware. But it presents a virtual machine abstraction that is similar - but not identical - to the underlying hardware. This type of semi virtualization is dubbed by the makers of Xen as para-virtualization.

The benefits of using para-virtualization over full virtualization are the improved performance and strong resource isolation on uncooperative machine architectures like x86. Of course, there is a down side to it too in that you need a specially compiled Linux kernel to successfully run Xen on Linux. A comparison of Xen over other virtualization technologies (like VMware and Usermode Linux) has already been published.

Xen Live CD - A Review

Recently, a Live CD was released to showcase the power of Xen virtualization. I had downloaded the Xen Demo Live CD ISO image (503 MB) from their website and burned it on to a CD in order to give it a trial run. What follows below are my experiences in trying out this very promising virtualization technology.

The Xen Live CD comes with two images: Debian Etch and CentOS 4.1. When I booted using the Live CD, I was presented with the GRUB boot loader which gave me a choice of booting either of the two systems. I selected Debian Etch and the booting proceeded without any problem. It took around 3 minutes to present the GUI login screen. Xen live CD uses GDM as the display manager and loads the Xfce desktop. When the gdm (Gnome display manager) was fully loaded, you are presented with the login screen where you are prompted to log in as user 'root' and password 'xensource'. Once you are logged in, you are presented with two open applications - one an X terminal and another giving a real time data of the virtual machine status (see figure, left).

Next I decided to create a virtual machine for the CentOS Linux distribution inside the Debian etch distribution. For achieving this, you have a command line utility called xm. I created the CentOS image by running the command :

# xm create -c /root/centos-conf name=centos_1

It gave an error, saying that it couldn't find enough memory to load CentOS and that it needed at least 96 MB for the same when there was only 17 MB available. The machine on which I tested Xen is a Pentium IV 256 MB RAM machine. At this point I realized that almost all the memory on my machine was allocated to Debian.

I figured out that one can reduce amount of memory allocated to the virtual OSes by using the same xm utility. For that you have to find the domain ID of the virtual OS whose memory allocation you want to change.

# xm domid Debian_os1
0

Now that I got the domain id of the Debian etch virtual os, I reduced the memory allocated to it to 98 MB as follows :

# xm  mem-set 0 98

The above command reduces the memory allocated to the domain ID 0 to 98 MB. Thus I succeeded in reducing the memory allocated to the Debian etch os to just 98 MB. Which meant at least 100 MB memory was freed in the process.

After that I again tried creating the CentOS virtual system. The previous low memory error was rectified but CentOS started in the paused state and I set about figuring out how to unpause it - which was quite simple as finding the domain id of the centos_1 image and then unpausing it using the universal xm command.

# xm domid centos_1
2
# xm unpause 2 

That done, eventually I got the CentOS login screen shown on the right.

Of course, if I have enough memory, I can start any number of these virtual OSes following the above methods. Xen uses VNC to display the virtual OS. So if you are starting say 10 virtual OSes, each will have its own VNC window. You can even start Xen on a server and then access a complete independent OS using a VNC client from a remote machine.

Uses of Xen Virtualization

Here are a few ways I figured out how Xen could be put to good use.

• If you are a student interested in getting hands-on networking skills, then you can set up your own virtual networking lab on your home computer provided you have at least 1 GB RAM. Using three or more virtual OSes, you can set up a virtual network and try out tasks like routing, bridging, setting up gateways, running firewalls, subnetting your network and more, all in the safe confines of a virtual environment.
• As a frequent netizen, you must be aware of the rumors that spread around two months back, of a certain very popular public company which planned to bring out its own operating system based on Linux. Of course, the rumor turned out to be a dud. But if such a project were to kick off, then it will most probably be using virtualization technology like Xen. Using Xen, each user can be given his own copy of a OS complete with root privileges. And since Xen is using VNC to display the desktop, it is most suitable for a network OS.

• Kernel developers and debugging specialists in the kernel space will find Xen useful because they can compile code and try out things on the virtual system without affecting the parent system.
• Application developers on the Linux platform can test their applications on different Linux distributions at the same time by running copies of the distributions simultaneously using Xen on their PC.

Current drawbacks of Xen Virtualization

• Needs to enable virtualization in the parent Linux kernel which, at this time, requires recompiling a kernel from source. But it is bound to change when Intel supports virtualization at the hardware level on more of its CPUs.
• Needs a good amount of memory for it to be of any use to anybody. I would recommend at least 1 GB memory even though, with a little bit of tweaking like I did above, you might be able to use it with less than 256 MB RAM.

• It is a relatively new technology (when compared to products like VMware which do full virtualization).

Comments (9 posted)

New Releases

Terra Soft Launches Most Polished Yellow Dog to Date

Terra Soft Solutions has released Yellow Dog Linux 4.1 with beta support for Apple G5 PowerMacs with dual core CPUs, basic 64-bit development and runtime support, and much more. Click below to see the entire press release.

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Damn Small Linux Releases Version 2.1

Damn Small Linux has released v2.1 with many improvements. See the change log for details. (Found on DebianPlanet)

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Distribution News

Mono added to Fedora Core

The January 10 Rawhide report (click below for the full text) includes some interesting changes. It seems that Mono, beagle, f-spot, and tomboy have been added to the distribution. Mono (and applications based on it) have long been left out as a result of patent concerns; there has been no official word on why things have changed.

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Debian xlibs-dev Mass Bug Filing

Xorg 6.9 is now in Debian unstable. "With this upload, the xlibs-dev metapackage is no longer built. I mailed debian-devel-announce about this back in November including the rationale for this decision. What this means right now is that a very large part of the archive that build-depends on xlibs-dev will FTBFS, and as such we have a lot of new RC bugs on our hands."

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Fedora-netdev FC4: kernel-2.6.14-1.1656_FC4.netdev.7 is now available

The latest Fedora-netdev kernel is available. Click below for the full change log, or check out the diff file.

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latest -git kernels available for Gentoo

Greg Kroah-Hartman has made it easy for Gentoo users to access the latest kernel -git tree. "Well, now there is a kernel package called 'git-sources' that you can install that will provide this. It should be updated every morning (my time zone, not necessarily yours), with the latest nightly -git kernel snapshot."

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Debconf6 Talks Announced

The annual Debian Developers Conference (DebConf) for 2006 will be held in Oaxtepec, Mexico from May 14th to May 22th 2006. Its target audience is mainly Debian Developers and contributors to the project, although Debian users are welcome to attend as well. The talks that will be held during the conference have already been selected and are listed here.

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New Distributions

IBLS

IBLS (Itty Bitty Linux Server) is a compact, easy to use webserver that you can run from a live CD, even on older hardware. It will run on a P133 with 32MB RAM, or possibly less. IBLS got its start in the UK, using Damn Small Linux as a base. It has since been rebuilt from scratch by an international community of developers. IBLS is modular and uses its own package management system, designed to run from the CD or from a hard drive. IBLS was updated December 31, 2005 to use the 2.6.14.5 kernel. Click below for more recent changes.

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Distribution Newsletters

Debian Weekly News

The January 10 issue of the Debian Weekly News is out. This week's topics include the status of non-free firmware, changes on the technical committee, integration of the amd64 port, and more.

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Fedora Weekly News Issue 28

This week Fedora Weekly News covers Fedora Community Survey Results, Long-term plan for Fedora logo usage, Looking for Fedora LiveCD Developers, RFC: kernel-modules in Fedora Extras, Interview with kde-redhat Project Leader, and several other topics.

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Gentoo Weekly Newsletter

The Gentoo Weekly Newsletter for the week of January 9, 2006 covers the upcoming FOSDEM conference, Lithuanian translators needed, a portrait of Andrea Barisani, and more.

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Ubuntu's 11th MOTU Report Available

The 11th issue of the Ubuntu Masters Of The Universe Report is available, with a look at what's new in the Ubuntu Universe. (Found on DebianPlanet)

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DistroWatch Weekly, Issue 133

The DistroWatch Weekly for January 9, 2006 is out. "We had a quiet week, only disturbed by new releases from Arch Linux and DragonFly BSD. We'll take a critical look at the latter, especially from the perspective of a desktop user, but don't expect much praise for the new version. In other news, the Fedora project has started testing its new rescue CD, Gentoo has published a HOWTO on creating a Gentoo LiveUSB, and Puppy is preparing for the launch of Puppy2, a major update. Among the distributions newly included on DistroWatch we have three live CDs: ArcheOS for archaeologists, Arudius for penetration testers, and Xenoppix for the fans of the Xen technology."

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Package updates

Fedora updates

Fedora Core 4 updates: gimp (update to v2.2.10), util-linux (bug fixes), ruby (new upstream release), openoffice.org (2.0.1 for FC4), gnucash (update to v1.8.12), eclipse (bug fixes), tzdata (prepare for 2007 DST changes), less (update to less-394), dhcp (bug fix), lftp (bug fixes), xterm (bug fixes), postgresql (update to PostgreSQL 8.0.6), system-config-bind (bug fixes, Serbian translations), hplip (bug fixes).

Fedora Core 3 updates: ruby (new upstream release), less (update to less-394), postgresql (update to PostgreSQL 7.4.11), system-config-bind (bug fixes, Serbian translations).

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Mandriva updates

Updates for Mandriva Linux: hal (2006.0 - improves card reader handling), libpaper1 (Corporate Desktop 3.0 - include library), kat (2006.0 - bug fixes).

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Trustix updates

Various bug fixes are available for Trustix Secure Linux 3.0 and 2.2: spamassassin (3.0 only), kernel, perl and apache, mailman, nmap and samba.

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Newsletters and articles of interest

All About Secure Apt (DebianPlanet)

DebianPlanet reports the existence of a how-to document for secure apt in Debian. This document explains the use of strong crypto in Debian's unstable and testing branches.

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Building Binary PC-BSD Packages (O'ReillyNet)

O'ReillyNet covers the process of adding extra packages (PBIs) to a PC-BSD system, assuming that the desired package is not currently included in the available Ports. "While casual users won't be making their own PBIs, you don't have to be a programmer to do so. If you have basic Unix skills, are comfortable with the FreeBSD packages collection, and have a meticulous nature, you can easily create your first PBI in the space of an afternoon. This article assumes that you are working on an existing PC-BSD system."

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Interview with Vincenzo Ciaglia, author of Netwosix Linux (OSSblog.it)

Here's an interview with Vincenzo Ciaglia, author and main developer of Netwosix. "Is Netwosix derived from some already existing distro or is it built from scratch? Vincenzo Ciaglia: The 1.x Branch is completely built from scratch. Branch 2.x, however, is partially based on Crux Linux, a lightweight and versatile distro, intended for desktop systems."

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My desktop OS: Xandros (NewsForge)

NewsForge hears from a Xandros fan. " About a year ago I installed Linux on my desktop at work. I am a database administrator for a PeopleSoft and Oracle shop and I spend a lot of my time remotely logged in to our servers. I decided to try Linux because I had become frustrated with Windows not being able to things like multiple desktops, forwarding the display of a remote server onto your box to run apps remotely, and connecting with SSH. Fortunately, my management is far more interested in having happy, productive employees than what operating system people use so they were willing to let me experiment. Today, with Xandros, I have a good solid desktop, and I don't worry about viruses, spyware, and adware."

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Linux newbies get a helping hand (ZDNet)

ZDNet takes a look at a Linux Distribution Chooser that aims to help newcomers choose a Linux distribution.

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