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I just ordered a cheap Dell PE1425 to run as a xen dom0.

Want to spawn some vm's and test configurations out and what not. Nothing crazy. Ultimately, I want to use it to create VM master images to convert to AMI's for EC2...

What's the preferred host os? We primarily use CentOS in production, and have Ubuntu installed here and there around the office... or should I be considering another distro or OS (BSD?)


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up vote 6 down vote accepted

Unless you're going to need a very recent release of Xen, you're probably best off with CentOS. It supports Xen out of the box (install the Virtualization group) and has a lot of support documentation such as the Red Hat Virtualization Guide. It also includes the Virtual Machine Manager GUI tool which is extremely useful for getting started quickly.

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Xen has a bit of a weird background. Ever wondered why - for example - Fedora 11 cannot function as a Xen host, but only as a guest?

Xen development has always been out-of-kernel and requires massive patching your kernel if you use a a current one. CentOS (and RHEL, for that matter) are based on kernel 2.6.18, for which excellent Xen support exists, because Red Hat supports that specific kernel to be a Xen dom0.

Newer kernels than 2.6.18 can - and probably will - be problematic. Check this article on, for example. Note that is not impossible to use Ubuntu as a Xen host, but I certainly wouldn't recommend it, and neither would, in the end, the author of the aforementioned article.

If you want to use a Debian based distribution for a Xen server, use Debian, not Ubuntu. That said, I would recommend a Red Hat based distribution (more specific CentOS) anytime, because of the fact that RHEL5 (and thus CentOS5) is an enterprise class distribution, which is marketed (amongst others) for it's Xen capabilities. RHEL5 (and thus CentOS5) will be around for a long time. Otoh, it is likely that Red Hat will drop Xen eventually. KVM seems to be the future.

Anyway, to make a long story short: go for CentOS5. Everything for a Xen server is in there, it is packaged very well and it just works.

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Fedora dropped support for dom0 Xen due to the maintenance burden in forward porting the patchset to keep up with the regular kernel. Instead they have focused on getting the paravirt_ops functionality into the mainline kernel to support Xen. Michael Young on the fedora-virt list has been doing experimental dom0 pvops builds for Fedora Rawhide ( but they obviously aren't suitable for production. – Ophidian Jun 24 '09 at 20:40
@Ophidian: it was a rhetorical question, actually, but you are completely correct. ;-) There are some excellent articles in the paid-for part of about this. I think they were published last month or so. – wzzrd Jun 24 '09 at 20:45
Didn't know about the dom0 repo's btw, which are pretty cool. Thanks. – wzzrd Jun 24 '09 at 20:46
@wzzrd: I figured as much, but thought the extra context might be useful as well :) – Ophidian Jun 24 '09 at 20:51
For more info about the experimental dom0 kernel, there are some useful discussions about it in the fedora-xen (Primarily Dec 2008 and Feb 2009) archives, and more recently in the fedora-virt archives (Feb 2009 to present) – Ophidian Jun 24 '09 at 20:54

I personally think that both Ubuntu and Centos aren't great long term prospects for Xen. Xen on Ubuntu has been pretty flaky for the last few versions and Ubuntu seems to be ignoring it. Xen support in Centos/RHEL 5.x is pretty good, but getting a bit dated and Xen is no longer really part of Redhats future either.

I would recommend Debian. Etch had good Xen support, and Lenny does too now. And Xen is pretty easy to build from scratch on Debian as well. But best of all, Debian developers are continuing to support Xen. SUSE sounds like a good option also although I'm less familiar with it.

Xen support from other distros will probably improve a bit if the new pv-ops dom0 Linux kernel branch stabilizes more, and things will probably improve a lot more if the pv-ops dom0 changes ever make it into the mainline Linux kernel (don't hold your breath for that though).

And for a slightly more exotic Xen dom0, you might even want to try OpenSolaris. I haven't actually used it myself though :)

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Since this box will probably dedicated XEN server, you don't want an OS that installs (even if it is not used) all kinds of other software, so you are probably better of using a stripped down debian or something like that.

Although BSD is my preferred choice for Os, I wouldn't recommend it in this case. As far as I know only NetBSD is capable of being a XEN host, however you are better of using a linux kernel since the multi CPU performance is slightly better then that of NetBSD.

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