Thanks @bedna & @dmt for further assistance. Getting out of my depth here, also out for most of today, so all I’ve done so far is delete /etc/shadow.pacnew.
I need to learn up on the other stuff. I’m reasonably familiar with nano, less so with vim and not at all with meld.
This should help:
https://wiki.archlinux.org/title/Pacman/Pacnew_and_Pacsave#.pacnew
meld is a GUI, in the extra repositories:
$ pamac search meld
[...]
meld 3.22.0-2 [Installed] extra
Compare files, directories and working copies
…so can be installed using:
pamac install meld
It’s also one of the easier options IMHO.
On top of that, if you want to use meld as the diff software on your system, set the env variable. I do it in /etc/environment
Example:
EDITOR=/usr/bin/nano
SUDO_EDITOR=/usr/bin/nano
DIFFPROG=/usr/bin/meld
VISUAL=/usr/bin/nano
This means that if you run pacdiff -s, meld will be used as default.
Thanks for all the above.
I came hoping for a quick fix - now I’m in for further lessons in Manjaro! So be it!
i would check these 2 pac files:
this one is for the display manager:
also the pamac and pacman should be checked out…
i would not mess with every pacnew, especially the shadow one…
you could install another DE, but this looks like something more ‘deeper’…
Another thought I had, as a temporary workaround till I have more time, is to use the chroot environment to launch applications from my normal system. So I tried opening firefox, but immediately ran into authourisation problems:
[manjaro-gnome /]# su nick
[nick@manjaro-gnome /]$ sudo rm /etc/shadow.pacnew
[sudo] password for nick:
[nick@manjaro-gnome /]$ firefox
Authorization required, but no authorization protocol specified
Error: cannot open display: :0
[nick@manjaro-gnome /]$
So two questions:
Seeing as the chroot environment is extremely dangerous, and not at all for running GUI apps, as you can see with
I highly doubt it.
But I have to say:
the title of the thread is:
Hoping to avoid reinstalling
…and you’ve stated:
I think reinstalling might go quicker.
There doesn’t seem to be a quick solution to your problems otherwise.
/home on a separate partition?Three simple questions, which should help others guide you on what to do next.
Good luck.
Out for the rest of the day now. Will check back this evening for any further suggestions. I can see how a fresh install is probably the way to go. Why is the timing of these things always so damned inconvenient?!
Because otherwise it would not have been a crises… 
and how we deal with crises’ defines us…
OK, that was my wise man moment for the day…
You know what they say: Sh… These things happen while we’re busy making other plans.
Any system which depends on human reliability is unreliable.
And
If there is a possibility of several things going wrong, the one that will cause the most damage will be the one to go wrong.
There’s one last thing I want to try before giving up.
I read this morning that there can be issues with auto-login in Gnome. I had my login set to auto and it occurs to me that that could be at the root of the problem. Presumably there is a setting somewhere in a config file where I could chroot into the unstable system and disable auto-login. Seems worth a shot. Could someone please tell me where to find the relevant file(s)?
You could look for /etc/gdm/custom.conf if it exists, and likely change AutomaticLoginEnable from True to False under the daemon section:
[daemon]
AutomaticLoginEnable=True
AutomaticLogin=username
This file and it’s location may differ depending on the DE used, but for Gnome and GDM, that’s probably a good place to start looking. Obviously, if the file doesn’t exist, then look elsewhere.
I hope this helps. Cheers.
Thanks @soundofthunder and @Mirdarthos for that very helpful info. Sadly disabling auto-login hasn’t made any difference.
I think I’ve run out of road. Thanks for all the help along the way - really good support and much appreciated.
I’ve set myself up as a user on my partner’s machine so I can continue with immediate essential work without too much inconvenience, then when I have more time I shall rejig my drives, adding a new one, and do a fresh installation.
When you have that time, consider having /home on a separate partition. This will allow you to reinstall with less complication in future. It would require that you perform manual partitioning during Manjaro installation; which only takes common sense, really, which you seem to have. Cheers.
You have gotten a lot of great help even if it hasn’t produced the results you were looking for, so, this is going to sound a bit pedantic, but getting a small external drive like a Wd-Passprt and using TimeShift maybe a real help in the future. This is what I do, and it might work for you, too.
Thanks, and yes, I’ll definitely do that. I’d thought that by having key folders on a separate drive, I would not be too bothered to overwrite everything else in home folder, but after a few years of lax housekeeping, how wrong I was! 