Kudos to the Debian Xen Team for getting Xen ready for lenny in time.

As I wrote earlier, my desktop runs a Xen dom0 under Debian etch. The various domU's run Debian lenny among other things.

While doing a (much delayed) upgrade of these domU's I noticed that there was a xen-linux-2.6.26-1-amd64 package available under lenny. This made me exclaim, "Three cheers for the Debian Xen Team! Time to upgrade and test things out."

The upgrade to lenny went smoothly --- almost. Here are some sticky points which are at least partly due my own goof-ups and perhaps due to some aspect of the xen package upgrades. Since I am not clear about where the "blame" lies, I haven't yet filed bugs!

• xen-utils-common version 3.2.0-2 needs the newer xen-utils-3.2-1. In particular, /etc/init.d/xend fails to run with xen-utils-3.0.3-1. The newer package is "Recommended" by the Xen 3.2 hypervisor, so I should have installed it but perhaps it should not be possible to avoid installing it.
• xen-utils-3.2-1 depends on a large number of packages since it includes the functionality of xen-ioemu-3.0.3-1. This is why I tried to avoid installing it --- my mistake.
• The xen domU configurations created using xen-tools version 2.8-2 did not (I think!) have a "xencons=tty" parameter appended to the kernel command-line. This does not cause a problem with the 2.6.18 Xen kernels but caused the 2.6.26 kernels to fail to assign a usable device to the domU's tty1. Since some of these domU's did not have a running ssh this made it impossible for me to login to them! :-(

The bottom line is that to upgrade an etch dom0 to a lenny dom0 (on amd64) you should make sure that you install the following packages:

xen-linux-system-2.6.26-1-xen-amd64, linux-image-2.6.26-1-xen-amd64, 
linux-modules-2.6.26-1-xen-amd64, xen-utils-common, xenstore-utils,
xen-hypervisor-3.2-1-amd64, xen-utils-3.2-1

If you install all recommended packages, then just installing the first package above will pull in all the others; however, like me you may be a no-one-recommends-packages-to-me kind of person! :-(

Secondly, you should add the "xencons=tty" kernel parameter to those domU's which will boot the lenny 2.6.26 xen kernel.

These are minor issues considering that anyone who runs a Xen machine circa 2008 should be knowledgable enough to be able to fix them. However, they could cause unpleasant hiccups for some people so I'm documenting them here.

Update: One thing which is required to run the Xserver when your graphics card uses shared memory is to limit the memory used by dom0. To do this you pass an option like "dom0_mem=128M" to the command line for the xen hypervisor in grub's configuration file `menu.lst`.

Update2: The kernel linux-image-2.6.26-1-xen-amd64 (Debian version 2.6.26-8) has a nasty bug which makes dom0's and domU's using this kernel crash when they access memory beyond that which is available as RAM. So I have had to revert to the etch kernel linux-image-2.6.18-6-xen-amd64 which works fine with the rest of lenny.