Do you use Debian as a desktop?

Would it be possible to switch from Ubuntu to Debian without having to reinstall the whole system?

I hope something like updating sources to debian unstable and doing apt-get upgrade should just work, but am afraid to try it on the running system.

It can be done, but don't attempt this unless you're ready to fix a ton of tiny problems all over the place. Backup your data and move it over to a fresh installation instead.

No, absolutely not. Although people colloquially refer to Ubuntu as Debian with a little stuff sprinkled on top, parts of the underlying architecture are fundamentally different. Here's a video of someone giving it a go. (Doesn't even boot)

https://www.youtube.com/watch?v=x4dD_cbV5aw

That would not be advisable. If you do end up moving to Debain but start missing features, Linux Mint Debian Edition (LMDE) may be a better fit.

Looking at the way Canonical is operating, as a Linux Mint Cinnamon user, I sure am glad they're building for a "if Ubuntu was ever to disappear" world.

"Its goal is to ensure Linux Mint can continue to deliver the same user experience if Ubuntu was ever to disappear. It allows us to assess how much we depend on Ubuntu and how much work would be involved in such an event. LMDE is also one of our development targets, as such it guarantees the software we develop is compatible outside of Ubuntu."

https://www.linuxmint.com/download_lmde.php

Would be wiser to switch to Fedora, Red Hat has way more funding than Canonical or Debian will ever have

Like others recommendations here, I also switched with fresh installation of Debian. If you don't do this you would end up with broken system and also you would not see what all debian has to offer.

What you should be able to do but I have never tried in practice is to keep your home directory. Most "novice" computer users like me, would only need one user anyway although this should work for multiple users as well?

I think in theory at least if your username is anthropodie, you should be able to copy /home/anthropodie to an external hard disk just for backup, install your new distro, set up your new user and copy your user home directory back. Anyone tried this?

The approach I've followed for many years is to have /home mount on a separate partition from anything else. Then when you do any kind of fresh install or upgrade, you only have to make sure that partition doesn't get touched (and usually that's the default) and all is well with the world.

It would be slightly more work involving parted (or whatever partition manager you prefer) to create a new partition, resize existing partitions, etc., but quite doable (if tedious and time consuming).

By clean setup I mean, reinstalling /

/home is kept intact. After installation of apps on new setup I don't even have to configure them most of times because they can find their config directories in /home/myuser/

but debian iirc has only one partition by default, no?

That is not true. I have configured /home on Debian.

I used to keep my home dir on a separate partition, but I was always worried I'd wipe it out during the OS install.

Instead I backup my home dir with borg backup to drives/cloud.

I have a script to borg mount my most recent borg backup, so when I set up a new OS install, I just run the script and copy my files over from my backup to my computer's SSD.

I love this method because I can easily install a different SSD, switch to a new computer, or just do a clean OS installation very easily.

I did exactly that about a year ago (except it was testing instead of unstable). You need to pass some extra flag to APT because Ubuntu and Debian use different version schemes, so you wouldn't get updates anymore -- might have been '--reinstall', but don't quote me on that.

It worked quite well for me, although there were a few issues (for instance, I didn't get kernel updates anymore, and when I fixed that, the Wifi driver was missing). There are probably still a few issues that went undetected and might cause problems later.

It's certainly possible, but I wouldn't recommend it unless you're willing to spend quite some time on it. And don't count on it working at all. (And backup your data. I didn't, and got lucky, but in retrospect, that was irresponsible.)

Possible? Yes.

A good idea? No. If you need to ask, you will have regrets.

A fresh install would be faster, easier, safer, and more secure.

Ubuntu 18 LTS (pre-snap) until next April then on to debian for me.