Ubuntu – Convert a 64-bit Ubuntu server to a 32-bit Ubuntu server

32-bit64-bitUbuntu

We have an Ubuntu server vmware-instance which appears to be installed with the 64-bit version.

Unfortunately we now want to move it to a 32-bit only host, so the current installation will not run. The installation is rather tweaked, so I'd really, really prefer to have the current installation converted instead of doing a fresh installation.

Is there a reliable way to get 32-bit versions of everything and convert the kernel, or should I completely drop the idea?

Thanks for all help.

EDIT: The primary purpose of this Linux instance was to provide a CVS repository. After careful consideration we decided to migrate from CVS to git instead of doing the 64->32 bit exercise.

Best Answer

I suspect that there is no easy, stable, reliable, automated way, as it isn't something that is going to be needed often enough for it to be worth spending a lot of time developing and testing, and doing it manually would probably take longer than simply rebuilding the VM's install from scratch.

You can speed up the rebuild to a certain extent though, you can make sure you have all the same packages installed by running

sudo dpkg --get-selections | grep '[[:space:]]install$' | \awk '{print $1}' > package_list

on the old VM, transferring the file over and running 

cat package_list | xargs sudo apt-get install

on the new VM.

Then copy the old VM's /etc/ tree over to the new machine (not as /etc - drop it somewhere temporary) and use a diff tool to locate differences you need to transfer over. The reason not to just bulk copy /etc into place is that there may be slight differences in the default config for some 64bit/32bit packages that you might want to at least look into rather than blitzing without knowing. For a start /etc/apt/sources.lst will need to differ. (Even if doing this to duplicate a 32 bit install to another 32 bit install I'd still not just copy /etc wholesale - doing a diff like this gives you the change of finding things that are no longer relevant and should have been purged for clarity)

Once that is done copy over /home to regain any user specific config & data, and anything like /var/www if you have files served by HTTP from there, and so on, and you are pretty much done.

I used the above to replicate one 32bit install as another 32bit install, but it should work just as well between architectures. You might find some packages cause the apt-get command to warn you about not finding the package. Some of these will be 32-bit compat packages that won't be present in the 32-bit repo obviously (just remove them from the package list and rerun) and some might be packages that have explicitly named 32 bit and 64 bit packages (in which case find the right name using the search on packages.ubuntu.com, edit the package list, and rerun apt-get).

Of course this will not replicate anything you did not install from the Ubuntu repositories, so you'll have to redo anything like that manually, but otherwise this process may save you a little time. Also, before running apt-get, make sure the new VMs sources.list has the same repositories enabled as the old one, or you'll get a lot more package-not-found issues from apt-get.

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