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[Xen-devel] auto-installing debian on xen on debian with debian-installe

To: Debian Install System Team <debian-boot@xxxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] auto-installing debian on xen on debian with debian-installer preseeding
From: Philip Hands <phil@xxxxxxxxx>
Date: Wed, 29 Jun 2005 13:06:58 +0100
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Hi Folks,

Hopefully this will be of interest to some of you.

I've put together a debian-installer preseed setup, that allows (among
other things) one to do a non-interactive install of Xen with a minimal
Debian as it's Domain0, sets up LVM so that one can create disks for other
domains and then lets you run the debian installer in a new domain so that
you can then install Debian instances.

For the Xen folks, this should turn into an easy way for people to dip
their toe in the water without having to read lots of tedious
documentation, and also be a pretty decent way of doing real deployments
(although I'd have thought that using debootstrap for the secondary
installs might make a bit more sense, but at least you get a machine where
you can do that without any effort)

For the debian-installer folks, you might be interested (or horrified ;-)
about how I managed this with only slight tweaking to the sarge release
version of debian-installer (given that it doesn't support LVM, so I had to
do a bit of scripting).  Also, there's some (at present rather kludgey)
tweaks that are needed to allow debian-installer to work within an
unprivileged xen domain.

Given that you could have a load of diagnostic tools in Dom0, and then fire
up one or more installs in subsequent domains, with the (theoretical)
possibility of monitoring what they were doing from the outside, this could
turn into a nice environment for testing debian-installer.  Although at
present it's significantly less helpful than a real machine because I don't
see any way of getting to /dev/tty[234] under xen, so debugging is
currently a right pain,

Anyway, here it is:


There are some HOWTOs and top page includes a README.html.  It's still a
work in progress, so I may well reorganise the layout of the subdirectories
at some point (it's mildly chaotic at present).  The idea behind the
structure is that one can turn up to a site with standard(ish) boot media,
and have the preseed system determine the site it's running on (or you can
tell it by hand) and then install the requested machine type.

The xen setup described above will get installed if you specify a machine
type of "xen0", which you do by booting the mildly tweaked boot media, and
specify this at the boot prompt:

  boot:  auto26 local/cfg=xen0

the tweaks to the boot media are described in the HOWTO-{PXE,CD,USB}.txt
files, the details about the xen setup are described in the HOWTO-xen.txt

If people want to customise this to their own needs, they can either grab a
copy and point the install media at their local server in the initial
preseed,cfg, or they're welcome to have write access to the svk repository
where all this resides (once I work out a clean way of admin-ing that).

Anyway, feel free to have a play, and I'm very open to suggestions on how
to improve things.

Things that are currently less than perfect:

  Xen:  it would be nice to know how to access the other virtual consoles
        of a XenU domain from Dom0, so one could get at the shell if an
        install goes wrong.

      the current setup uses side effecting include-commands in a
      positively abusive manner to set preseed variables under scripted
      control --- there must be a better way (or we should add one)

      I'd like to be able to say "include this preseed file if it exists,
      but don't give me an error if it doesn't" or alternatively "include
      this file if it exists, otherwise include that one"

      It would be nice to have a script run late enough in the base-config
      so that one could reboot (in this case for the first boot into Xen)

Cheers, Phil.

P.S.  Please only reply to one list unless you're pretty sure that you're
      saying something of interest to both.

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