Play Machine Online Again with Xen 4.0


My SE Linux Play Machine [1] has been offline for almost a month (it went offline late May 30 and has just gone online again). It’s the sort of downtime that can happen when you use Debian/Unstable.

For a while I’ve been using a HP E-PC (a SFF desktop system with 256M of RAM and a P3-800 CPU) to run my SE Linux Play Machine. I run it under Xen to make it easier for me to watch what happens. I’ve had some problems with increased memory use in the Xen Dom0 in Squeeze [2]. The latest installment of the memory problems is when I discovered that I can’t run two copies of tcpdump (for tracing separate interfaces) at once on a Xen Dom0 that has ~110M of RAM – this seems unreasonable, I’m sure that back when a big server had 128M of RAM I could have done such things! So now I’m using a Thinkpad T20 with 512M of RAM for my new SE Linux Play Machine, it uses less power than most systems (probably even less than the HP E-PC) and is very quiet.

I was forced to install on a new system when I broke my GRUB configuration. GRUB-2 in Debian currently has no support for generating a configuration that will boot a Xen Dom0. You can manually edit the GRUB configuration to get this working, but if you get it wrong then you can make GRUB not even display a prompt and force a reinstall (as I did). As an aside it would be really handy if someone would create a CD or USB bootable image that does nothing but install GRUB. Such an image would ideally allow replacing the configuration of an existing GRUB, overwriting an existing GRUB installation (all files in /boot/grub get replaced), or formatting a spare partition (default swap space) and installing GRUB there.

My current solution to the GRUB problems is to use the old version of GRUB in the grub-legacy package. The old version of GRUB has always done everything I want so I don’t seem to be missing anything by not using the new version. I’m happy to refrain from using Ext4 for /boot and have no desire to have /boot on an LVM volume.

Most of the month of down-time for my Play Machine was caused by bugs in the SE Linux policy I’m developing for Squeeze, while they weren’t difficult bugs I haven’t had much time to work on them consistently. I’m still running the Play Machine on Lenny, but the Dom0 is running Unstable.


1 thought on “Play Machine Online Again with Xen 4.0”

  1. A grub2 script was posted to the xen-devel list this morning to generate the necessary entries. It’s a drop in script for /etc/grub.d and much better than the hack I threw together as a work around for my systems. I’m currently using it without any problems but YMMV

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