I’m a glutton for punishment. I’ll install software at the drop of a hat whether I need it or not. This is especially true about Linux desktop environments if they’re pretty enough. I looked at the latest KDE Plasma desktop, 5.26, and thought “shiney!” Because Linux Mint is based on Ubuntu, as is Kubuntu, I decided to install 5.26. After all, with apt, how hard could it be? Turns out an installation would be a bit of a mess. But I’ll get to that further down. First, I had to check to make sure my Linux Mint 21 installation was up to date.

mint ~ sudo apt update
Hit:1 stable InRelease
Hit:2 stable InRelease
Ign:3 vanessa InRelease
Hit:4 jammy-security InRelease
Hit:5 vanessa Release
Hit:6 jammy InRelease
Hit:7 jammy-updates InRelease
Ign:8 stable InRelease
Hit:9 jammy-backports InRelease
Hit:10 stable Release
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.

Great. Nothing needed to be updated. I then went searching for directions on how to add the necessary repo to my local apt so I could install the up-to-date KDE. I found what I thought was a good set of directions, checked to make sure the publication date was recent, and it was, and then attempted to follow the directions. Thus I ran the following.

mint ~ sudo add-apt-repository ppa:kubuntu-ppa/backports
You are about to add the following PPA:
Backports of new versions of KDE Platform, Plasma and 
Applications as well as major KDE apps for Kubuntu.

sudo add-apt-repository ppa:kubuntu-ppa/backports

This PPA will receive major version updates backported 
from later Kubuntu releases (and our development release);
so if instead you want early access to just point (bugfix) 
releases of the versions of applications shipped with 
a Kubuntu release, then our updates PPA provides those:
More info:
Press Enter to continue or Ctrl+C to cancel

Nothing out of the ordinary, so I typed Enter. Then this was displayed.

Warning: apt-key is deprecated. Manage keyring files 
in trusted.gpg.d instead (see apt-key(8)).
Executing: /tmp/apt-key-gpghome.ineZ8M22VJ/ --keyserver hkps:// --recv-keys E4DFEC907DEDA4B8A670E8042836CB0A8AC93F7A
gpg: key 2836CB0A8AC93F7A: public key "Launchpad Kubuntu Updates" imported
gpg: Total number processed: 1
gpg:               imported: 1

*sign* I’ve seen this once before. I wanted to install the latest GCC/G++ compiler tools (version 12), so I attempted to add that repo with the same method above, and got the same dire warning. Rather than stopping I bulled ahead trying to install the latest, only to wind up with something of a mess. When I went searching for the proper way to migrate to the correct way to add a repo, those directions were a convoluted mess. In the end I removed everything including the repo entries down /etc/apt. Fortunately there was a backup of /etc/apt/trusted.gpg, so I restored that backup. There’s a second entry for the new repo in /etc/apt/sources.list.d, which in this instance is kubuntu-ppa-backports-jammy.list, so that gets deleted as well.

I have no idea if, let alone when, I’ll try this again. But before I do it sure would be nice if the apt tools would provide a way to automatically convert the old deprecated way into the new-hotness way. The way it currently is is just bullshit.