32bit to 64bit "update" (was: Re: Plan for tomorrows (20070531) FESCO meeting)

[Matthias Saou]

Jesse Keating wrote :

> Upgrading from i386 to x86_64 is going to be a MUCH more difficult task.

Mostly OT, but this is something I had wanted to try for a while and
actually did last week on a server.

Doing it with yum or even rpm seems unfortunately pretty much
impossible, since x86_64 stuff won't install/run when still running an
x86, so scriplets would fail miserably. Too bad, since forcing a
minimal set of 64bit packages on the machine and rebooting it to
continue the procedure could have been nice.

The solution which worked for me was to rsync a clean x86_64
installation from an identical server as /root/foo, edit the few files
that need to be (ifcfg-*, /etc/hosts, /etc/sysconfig/network). Then
start moving the old root directories away and putting the new one into
place.

There are many directories that aren't much of a problem to move away
(/etc, /home, /var, etc. even /boot) and others that don't need to be
(/proc, /sys). But the trickiest one is /bin since you need "mv" to
finish the job, and the 64bit /bin/mv won't work.
What I did was "mv bin bin.32 && ./bin32/mv /root/foo/bin ." as the
last step... and it worked.
I don't know how to make the machine reboot without init being
available, though, but luckily I have switched PDUs that I can control,
so I remotely power cycled the server (run "sync" as early as possible,
it can't harm!).

I was really surprised when the server rebooted perfectly. I really
thought grub would stop for some reason, or some other problem would
prevent the server from booting... but no. A "new" x86_64 system up and
running.

That's how I went remotely from RHEL4 i386 to RHEL5 x86_64. YMMV of
course, and I really don't recommend doing it... but it *is*
possible ;-)

Matthias

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