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RHL with User Mode Linux kernel?



Possibly a nutty idea, but:

Has anyone ever tried installing RHL as usual and then swapping out
the Red Hat kernel for a User Mode Linux kernel and running one copy
of RHL "on top of" another, separate Linux installation?

Did it boot? - after some fiddling of course! How fast? Could you
connect to the host X server and run KDE? Issues that required
configuration changes?

I don't want to use a "prebuilt" image from the UML site, I want
to use the official RHL ISOs, so that I can set up the guest
system how I want it (and learn whatever's necessary to set up UML
"by hand" in the process).

I'd like to run an "almost-pristine" copy of RHL (current beta/release
version, and previous release version, which right now would be RH9)
"on top of" my main system (which is a mishmash of packages from
various RPM repositories). I think UML has something like a
copy-on-write feature which allows you to keep the guest system
pristine (like VMWare can).

This would be a godsend for: reproducing and filing bugs (rather than
having to annoy people by saying "Um, I've got a funny kind of mix of
packages from RH7,8,9, Rawhide and Severn here, with some extra custom
packages", I could say "This is the output on a freshly-installed RHL
system" - which makes the bug less likely to be caused by a system
configuration error); and for building RPMs for distribution (making
absolutely sure that the build is against a pristine system, so no
non-standard packages are there to screw up the build).

UML is also, of course, damn useful for trying out experimental or
in-development kernel patches/modules/kernels which might cause
kernel crashes or trash data, as long as they don't need direct
hardware access. Things like enbd, kernel hooks for userland
filesystems, etc.

All without having to reboot and without having to waste resources on
a second physical machine.

I used to use VMWare for trying and using out different distros, but
this is obviously closed-source and expensive. Also, from an
engineering point of view UML is a much cleaner approach than
VMWare's, for a variety of reasons.

Of course, the fact that the kernel is UML rather than the RedHat
kernel could be a source of differences, and UML can't do everything
that a real kernel can do (yet) but I still think it would be
valuable.

If there are a lot of configuration issues, perhaps a package could be
produced that sets up sensible defaults. OR EVEN - ambitious project
here - hack anaconda so that an ISO could somehow boot (with a little
helper script and an on-ISO UML image) AND install itself, all within
UML! That would be a fantastic hack! And it would be something to set
Red Hat apart from other distros (for about 1 version ;) [*]

-- 
Robin

[*] Actually, I've just found out that RH8 had a UML _kernel_
included, but this was dropped in RH9 due to patching issues, but it
will be back because it's in kernel 2.6 - see:

 "Red Hat Linux 9 Technical Changes - or when the RELEASE-NOTES are
 just not enough"
 http://www.gurulabs.com/RedHatLinux9-review.html




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