On Sun, May 13, 2012 at 2:33 PM, Russell Coker <russell@coker.com.au> wrote:

On Sun, 13 May 2012, Wen Lin <vwenlin@gmail.com> wrote:
> I had used a Live CD to boot the PC up and confirmed that all his data
> (/home) is in a separate partition, so a clean install of 12.04 will not
> loose his data completely. However, that would mean I have to spend lots
> more time re-installing all his extra programs, installing codecs,
> configuring his scanner, etc (that I'd spent many hours/days fine-tuning in
> the previous 11.10 install).
>
> So my question to the LUV'ers out there, is there a way I can do to get
> back to his 11.10 version? Any tips will help as I have not done such
> rescue before.

When using dpkg to upgrade a system (via APT or whatever Ubuntu uses) you
can't just downgrade. Downgrading an individual package is easy and should
always work, downgrading lots of them isn't easy and I don't think we
guarantee it to work.

If you boot from another device (USB or CD) then you can get chroot into the
filesystem (this can be expected to work in such situations of corruption) and
then run dpkg commands to get a list of installed packages. Getting a useful
list of packages to install after that situation will involve some manual work
as an upgrade between major versions always involves some packages being
removed and some new ones added. So a list of installed packages probably
isn't doing to match either the old version of Ubuntu or the new version.

Also after booting from another device you can make a backup of /etc which
should be useful in recreating the new system. Don't try doing a cp -a over
the new installation (that won't work and will probably give an unbootable
system). The thing to do is to do a fresh install and then run "diff -ru"
between the new /etc and the backup of /etc and then copy over whatever seems
appropriate. This is what I did the last time I had a system in need of such
a reinstall.

Good luck!

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