Kubuntu 18.04.2 LTS -> Ubuntu 19.04

[Paul Smith]

On Sat, 2019-06-15 at 02:52 +0200, Volker Wysk wrote:
> > It is definitely supported to use do-release-upgrade to move between
> > non-LTS releases; I do it all the time (I don't use fresh install
> > modes). However, unfortunately you can't skip non-LTS releases;
> > that's not supported.  
> 
> It's possible to upgrade from one LTS release to the next, skipping the
> non-LTS releases in between...

Clearly.  I guess I didn't word that as well as I should have.  I
meant, if you're moving FROM or TO *non*-LTS releases, you can't skip
interim releases.

So if you're upgrading from 18.04 LTS, your only supported options are
to go to 18.10, or wait for 20.04 LTS.

If you're upgrading from 18.10, your _only_ option is 19.04.  You can't
go from 18.10 to 20.04 LTS.

> > It should be _possible_ because all the packages will have
> > appropriate names... however of course at best you'll have a lot of
> > leftover Kubuntu packages lying around on your Ubuntu system.
> 
> I don't get this. Are you saying that the Kubuntu package names won't
> clash with vanilla-Ubuntu package names?

Right.  The libc package is the same in both, for example.  As best as
I understand it Kubuntu is standard Ubuntu with a bunch of other
packages installed.

It's probably wise to separate this operation into two steps:
upgrading, and switching from Kubuntu to Ubuntu.  I wouldn't try to do
them at the same time.

I would say your most likely to succeed method would be to FIRST switch
your Kubuntu 18.04 to vanilla Ubuntu 18.04.  That is likely the best-
supported transition: moreso than the non-LTS releases.

After that is all set and your system is running Ubuntu 18.04 well and
you've removed all the Kubuntu packages, then do the upgrade process.

> Or, what would cleaning out the obsolete stuff involve..? Is it just
> identifying no longer needed packages and remove them? Is there more to
> regard?

Well.  The only way to be 100% sure there is nothing crufty left lying
around is a fresh installation.

However, you can likely get 90% of the way there by just removing the
Kubuntu desktop packages.  Of course identifying them all could be a
chore.

I did a quick Google search and there are LOTS of articles discussing
how to switch from Kubuntu to Ubuntu without reinstalling.  Many of
them are for pretty old versions of Ubuntu but I expect they work more
or less the same way now.

Mainly, you first install the ubuntu-desktop package which should
depend on everything you need, then you switch your display manager to
GDM and your account login to Gnome.  Then when everything is working
(maybe you can look at running processes to make sure they are gnome-
related not kde-related) you can remove Kubuntu packages.

There is also very likely to be a bunch of user-specific customizations
left in your ~/.config and/or ~/.local directories.  Removing packages
won't help with that.  If you care you'll have to _very carefully_
remove that by hand (of course you shouldn't remove anything used by
packages you still use).

As I said I've never done this, so I can't give more than broad
outlines.