In my experience, I found the best way was to have a fall back plan, thats how I found out about blkid, lsblk and using/editing fstab.

When I started to use GNU/Linux I was lead/taught to use separate partitions for most of the main directories, like /usr /var /tmp / /boot /home and /usr/src and swap.

However, I don't always do that, sometimes I'll let the installer decide the amount and size of separate partitions,

and sometimes The system is contained on one drive as a single partition, with the exception of a swap.

I think I remember getting a question when installing, "what login manager" I wanted to use, I generally chose lightdm. (maybe because I prefer the programs with kde/plasma)

I have used slim, sometimes it is installed by default, I think it was when I did a minimum install from the live iso... xfce4 or cinamon.

I like to have choices. Usually I experiment with other distros or desktop managers and rather than risk destroying my main system, I'll use an old harddrive for the task. (but I'll detatch all the other HDD's before install, and reattatch them after install and setup.)

I'm glad you got your system working. All the best.

(btw, I did little of this by myself, forums thike this have taught me, and saved me many times.)

I stand on the shoulders of giants!

No probles, glad to help. It happens because of formatting.

During the installation process I always select manual partitioning (which is mandatory for me as I have a triple boot system), so I can choose the proper partition for /.
Being used to installers of previous installations would just make use of an existing swap partition (instead of reformatting it), I honestly didn't pay attention to what the Devuan-installer was doing with swapspace.
Will have an eye on that from now on.

Too bad that my experience is different from yours. Otherwise I could have just applied your fixes and most likely get it running.
On my system, elogind/libpam-elogind is already installed while consolekit is not.
Still, there is something wrong with slim as I just see a blank wallpaper.
My personal workaround is to use another DM and I can happily live with that.

I just wonder if I am the only one having problems with slim as it seems to be the default DM. At least I hadn't seen the option to choose another one during the installation (I might have overlooked it though).

That had been the cause.
After the installation of Devuan, the swap partition seemed to have gotten a different UUID which didn't match the previous one that was set in /etc/fstab in Bullseye.
I was able to fix it with your advice. Thanks a lot.

(I just wonder why that didn't happen the week before, when I installed AntiX on the partition that now Devuan is on.)

No probles, glad to help. It happens because of formatting.

The fix is:

$ sudo apt install libpam-elogind

The previous SM was consolekit, but that was deprecated in Beowulf. My experience was NOT identical to yours, although I DID have a GUI. What I did not have was any ability to elevate privilege (equivalent of sudo in the Terminal) and therefore could not login nor logout without recourse to a Terminal.

Check whether you are using consolekit or logind (the two are mutually exclusive).

As I understand the change, it once & for all got rid of libsystemd0 & thus (hopefully) the last vestiges of SystemD. It thus also required a second reboot after upgrade (just like Windows).

There is a good chance that during the install the uuid of the swap partition had been renewed/changed.

I know that can cause problems, slow start to the system.

You can check this with blkid and /etc/fstab, that the references are the same, and if not correct them and reboot.

As for changing configs, you may need to change or set a root password, A quick web search may give you a solution.

All the best.

That had been the cause.
After the installation of Devuan, the swap partition seemed to have gotten a different UUID which didn't match the previous one that was set in /etc/fstab in Bullseye.
I was able to fix it with your advice. Thanks a lot.

(I just wonder why that didn't happen the week before, when I installed AntiX on the partition that now Devuan is on.)

Ok, so you were directly dropped in a terminal, whereas I was in a GUI (background wallpaper without greeter) but was not able to do anything. Didn't even see a mouse pointer. I had to actively go to a termianal via CTRL+ALT+F2.

I just ran those 2 lines

...but they didn't return anything.
Reconfigured slim again to be the DM, rebooted but was again left with the background wallpaper with no possibility to do anything.

When I went to tty2, I found the following message (which may or may not be related):

[  120.058425] i915 0000:00:02.0: [drm] *ERROR* CPU pipe B FIFO underrun

So I went to tty3, changed back to ligthdm, rebooted and everything is fine (even though this error message is still present in tty2).

If it is of any interest to one of you (or the Devuan project itself) to find the cause of the initial problem, I am willing to dig deeper if there are any ideas/suggestions where and what to look for. After all, this is currently a test installation and not the system for daily work.
Otherwise I would probably go for option 1 as I currently have no clue where to start digging.

Out of curiosity I added "slim" to my Debian Bullseye installation and set it to be the display manager to be used.
It didn't work and I was just left with a background wallpaper just as in Devuan.
Changed back to sddm and everything was fine again. Hmm.

~$ sudo apt --fix-broken install
~$ sudo dpkg --configure -a

Ultimately, the whole thing was successful & I was back at a SLIM login + DE.

My upgrade was from Devuan beowulf rather than a fresh install like yourself. For that reason I did not mention it earlier, but then thought that perhaps another experience may offer a fresh insight.

The only thing I can think of is that it could have to do with the swap partition which is also used by Debian Bullseye.

It is well known that since systemd appeared sharing swap partitions between distros in the same box is trickier that it used to be. But I don't know how can be related the swap issue with your DE problem. I see two options: 1) everything works, let's move on; 2) let's dig deeper triying to find the root of the problem. It is now up to you

I know that can cause problems, slow start to the system.

You can check this with blkid and /etc/fstab, that the references are the same, and if not correct them and reboot.

As for changing configs, you may need to change or set a root password, A quick web search may give you a solution.

All the best.

The thing that keeps puzzling me:  I hadn't changed a single thing in this system.

The only thing I can think of is that it could have to do with the swap partition which is also used by Debian Bullseye.
During the installation of Devuan, the swap partition seemed to be recreated again by the Devuan installer and that must have caused a problem for Bullseye.
After the installation of Devuan, the start-up of Bullseye took a lot longer than usual and from what I've read, there was a problem with swapspace (I can write down the message if required).
When I was finally in my DE (in Bullseye), I started the taskmanager and noticed that there was no swapspace available.
So I fixed it with swapon. (But this problem is still present in Bullseye after every reboot.)
And since that swapon in Bullseye, I could finally log into Devuan without any problem, as the greeter is being shown.

I don't see any connecting link between both issues and I have no clue if that actually had to do with it.
I can just report what I've witnessed.
Now I just need to fix the problem in Bullseye (at least until I will completely replace it with Devuan).

I can provide the output which I saved in a txt-file but as the problem seemed to have solved itself, it's probably not of interesting anymore.
If it still is, let me know.

Thank you.

Ok, then there was a misunderstanding in the way that a connection was made to the internet. I never use wireless and to me reading about a "functioning ethernet connection" was synonymous to a working internet connection. My bad.
Still, to successfully perform an installation including a DE via a netinstall.iso, a working internet connection is an absolute necessity. Otherwise I wouldn't have gotten anywhere.
And having mentioned that the install went smoothly (and that the install of Debian Bullseye went uneventful, too), I assumed that it was obvious to everyone that internet access was not the problem (otherwise the installation would not have been possible at all).
That's why I wonder that you wrote this...

... as I had already mentioned in my very first post that the installation (including DE) was completed smoothly and uneventful.

If you read my 2nd post again, you will find that there was no lack of response.
I answered his only question ("what  is your video card?") and also gave feedback about why it can not possibly be missing drivers for the chipset governing the display (--> background wallpaper of the DM present; install of Debian Bullseye went without a hitch).

That's why I completely disagree with the point of your comment as it addressed something that I had already explained.
Can you now understand that I found it inappropriate and rather aggressive?

Accepted. Let's forget about it.

I was about to try the startx-suggestion but as I could log in all of a sudden (see above), I didn't carry it out.
But I looked into ~/.local/share and was surprised to not find an xorg-directory (only an icc-directory).

Thank you everybody for your support so far.

And to clarify: 13 year-old Intel integrated graphics chips do not need firmware.

The only thing possible was to move to a console via CTRL-ALT-Fx.

It is not a bad thing (It is best to use humour to clear the air, IMHO).

We can start to seek (posible) errors on the logs. First of all, could you post the output of dmesg run as root?

BTW: welcome

Doesn't using a netinstall.iso imply that one needs a funcioning ethernet connection to be able to download the necessary files for the rest of the installation? I thought that was obvious to everyone.

No, it is NOT obvious. Personally I also use a wired connection to my router, but my son's generation & younger use wireless, consider that to be normal & would rarely use Ethernet. WLAN & Bluetooth immediately mean non-free firmware whether on the motherboard or as an add-in card. Even mainstream intel & AMD CPUs need updating with microcode every so often (which is essentially firmware).

The point of my comment is that I found your lack of response to his attempt to help to be insulting to him. If you had replied that you made use of Ethernet & that therefore could obtain firmware on the fly during install, then he could have moved on to the next aspect to try to assist. If anyone can help then it is HoaS.

I'm sorry if you found my directness to be unfriendly.

What part of "You probably just need some firmware"" don't you understand?

Wow, that's sounds pretty unfriendly and rather aggressive.
Did you just have a bad day or is this the usual way in this forum to treat newcomers?

Doesn't using a netinstall.iso imply that one needs a funcioning ethernet connection to be able to download the necessary files for the rest of the installation? I thought that was obvious to everyone.
And no, there is no non-free firmware or drivers necessary for that old chipset because otherwise the netinstall of Debian Bullseye would not have worked.

The install for Debian Bullseye was not a problem whatsoever.
And during the install of Chimaera, I didn't see anything that would point to missing drivers or anything of the like.

I've installed lightdm afterwards and configured the system to use it instead of slim but to no avail.
Still no greeter, just a different background image.

(Did I expect too much in assuming that the Devuan installer is pretty much the same as Debian's minus everything that has to to with systemd?)