I have been using KDE with plasma ever since they were adopted as Ubuntu Studio’s standard GUI. I like Discover’s easy-to-use UI, especially the integration of snap and flathub repositories.
However, I have never been able to manage software sources with it. When I click on “software sources” I get a dialog titled “Run as root - KDE su”. Entering the same password I use to authorize updates in Discover produces a “Permission denied” error message, even though I can run the target application, software-properties-qt, from a console session as the same admin account I use for updates with a sudo command line.
This is apparently a well-known problem, to which I haven’t yet found a solution.
The reason for bringing it up now is that after weeks of frustration with Firefox snap (crashing) and not finding the flatpak version much better (won’t print) I wanted to install the native version from the Mozilla deb repository
Unfortunately, I couldn’t figure out how to add the repo in software-properties-qt, so I resorted to using apt (apt-get). I am not that well-versed in command-line usage and only managed this thanks to instructions found on the web.
I expected that the newly added repository would show up in software-properties-qt and that the newly installed Firefox version would show up in Discover, but neither is the case.
In desperation I have now installed synaptic in order to have a better idea what is installed. Synaptic does show everything installed, but I find the listing of every individual package overwhelming and prefer Discover’s application oriented GUI. Furthermore, even though Synaptic shows all the installed packages, it shows only the Mozilla deb repository under “Repositories”. The repositories listed in Discover appear in Synaptic only under “Origin” as filters and not as an editable list. I can’t find the snap or flatpak sources anywhere in Synaptic.
What are others using to manage software and sources under KDE Plasma?
I am running KDE plasma 5.27 and Qt 5.15.13
Interesting.
My Discover on KDE Neon doesn’t seem to have that.
I can go into settings and see Flatpak, Firmware Updates, Snap and KDE Neon repos but only Flatpak has a button to add one if its repos.
Maybe that button you have is a Ubuntu or Ubuntu Studio specific addition?
The “distribution packages” section does, however, list all my manually configured Debian package sources, e.g. for Signal.
That is indeed strange.
I also don’t see those things I have installed from additional deb repos.
pkcon sees them as installed so Discover’s Package-Kit backend should see that as well.
Maybe a bug in that backend.
You could check https://bugs.kde.org/ for an existing report, it sounds like something somebody might have already run into before
you are doing it right… there is currently no “one place” to go in the desktop settings to manage all the different sources.
assuming you have the appropriate backends, installed, snap and flatpak are managed right in discover and snap only has the one source so nothing to change there… flatpak lets you add repos in discover.
sudo software-properties-qt is where you can manually add additional respos like wine or backports under the other software tab if you have a convenient link.
as you noted, you can also add them via synaptic and the input there is more granular for details provided.
just remember to remove them before upgrading to a newer version of the OS as often those repos will not transfer without manual intervention anyway… in synapatic it’s often as as easy as changing the name of the distro.
This is, or rather was a bug in either Discover’s Apt support, or in Packagekit’s apt backend that happened when Ubuntu moved to using Debian’s new format for Apt sources files.
This has since been fixed in later Plasma releases, probably by late 6.3 but definitely in 6.4 version of Discover.
This of course will vary based on the distro involved, but for Ubuntu Flavours like Kubuntu, Lubuntu, and Ubuntu Studio, you’d normally use the Qt version of Ubuntu’s Software Sources utility, which is installed by defualt.
There normally would a link to this in Discover’s settings, but the bug also seems to break this. it isn’t even visible in Kubuntu LTS, or 25.04
A known workaround to get to this utility is to open the Driver Manager in System Settings, which is just a tab in the Software Sources tool. Or call the application directly from a terminal:
sudo software-properties-qt
This is exactly Discover’s purpose 
Synaptic is a GUI to apt itself directly, so it is a full-on package manager, as opposed to a software center.
Being an apt-only tool, synaptic doesn’t support things like Snap or Flatpak, just like apt itself doesn’t.
This unfortunately IS the easy way to do this fairly advance action., since it involves more than just adding a URL and some text, even more so for Mozilla, as it includes the necessary ‘pinning’ as well, which won’t have a GUI. At least Mozilla’s instructions do somewhat clearly state what each step does.
When you say you’re running KDE Plasma, that’s just the desktop environment - maybe you should copy from Info Centre available in the menu…
I’d suggest you’re actually running Ubuntu Studio 24.04.1 LTS, which would explain the older version of KDE Plasma (5.27is the LTS from Plasma 5 more than 2 years ago)… we’re mostly on 6.35 to 6.4 now since moving on to Plasma 6 early this year, was it February?).
The “Permission denied” error when trying to access Software Sources via Discover is a known bug affecting multiple KDE Plasma users, particularly in Ubuntu-based distributions. This occurs because many people like to run GUI applications as root using kdesu.
You will have a disjointed experience if you mix your tools.
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Discover shows Flatpak/Snap sources, and very limited DEB repository management - and DEB repos don’t work well in Discover because it uses PackageKit’s Apt backend.
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Synaptic only really handles DEB and APT repos, ignoring Flatpak/Snap sources.
For managing Repositories, use software-properties-qt in your terminal.
Flatpaks can be managed in Discover and Snap is limited to the default Snap Store in Discover.
You can use apt commands (or nala) in a terminal to install/update firefox.
- Muon is an alternative tool for Ubuntu Studio - a KDE-centric package manager that might work better.
However, I remember defaulting more and more to using the terminal for this kind of task - to get better control, better feedback.
In short, apt (or nala), flatpak and snap is how I would get full control over my packaging.
February 2024
Time flies.
Muon was long unmaintained and bit rotting, so was removed some time before *buntu 24.04. In any case, its repo management iirc was just a link to the Software Sources tool (software-properties-qt)
In my installation I do not find “distribution packages” in Discover. Here is a screenshot of Discover showing the kdesu error dialog. The “Software Sources” link is visible just to the right of the dialog:
As you suspected the bug launching software-properties-qt has already been reported:
https://bugs.kde.org/show_bug.cgi?id=483701
However, I don’t find a way to vote on it.
Aha, I also have that button if I install software-properties-qt
Interestingly I saw some log output in the system journal that could hint at kdesu being called with incorrect arguments.
Yes, that looks appropriate.
There is no such thing as voting.
And I see you’ve already added a comment 
Indeed, I am running Ubuntu Studio 24.04.1 LTS. Is this the info you asked for?
Operating System: Ubuntu Studio 24.04
KDE Plasma Version: 5.27.12
KDE Frameworks Version: 5.115.0
Qt Version: 5.15.13
Kernel Version: 6.8.0-62-lowlatency (64-bit)
Graphics Platform: X11
Processors: 4 × Intel® Core™ i5-2500 CPU @ 3.30GHz
Memory: 31.2 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 2000
Is it possible or sensible to try to upgrade KDE plasma, or is that likely to break other things?
Launching software-properties-qt from console hasn’t proved useful to me, since it doesn’t show the Mozilla deb repository I added through apt. What I am looking for is a single user interface that can show (and hopefully even manage) all of my active software sources.
I am on KDE Neon, which has the latest KDE stuff, e.g. Plasma 6.4.1, but it also based on Ubuntu 24.04, and I have the same issue.
A strong guess is that software-properties-qt is *buntu 24.04/Qt5/pyqt5/Plasma-5/etc and things don’t “mesh” with neon’s Plasma 6/Qt6 et al. Or the more current Discover just calls the tool with the wrong command string. That’s what I have assumed, but I don’t install or use that tool in neon normally, as I don’t need it.
This will run it without having to resort to straight sudo usage:
pkexec env DISPLAY=$DISPLAY XAUTHORITY=$XAUTHORITY software-properties-qt
This runs it using xwayland, fwiw.
Now, as I mentioned already, Kubuntu and Ubuntu Studio users can access this via the Driver Manager link in System Settings, since this tool is nothing more than a tab in the Software Sources utility ( software-properties-qt)
Trying to launch Driver Manager from System Settings produces the same kdesu error.
IAC, software-properties-qt will be of limited value until the known problem reported here gets fixed.
That is odd, as it works just fine in Kubuntu, and Ubuntu Studio is Kubuntu, in terms of Plasma. Maybe this is specific to this Ubuntu Flavour somehow?
To add another option for 24.04 – Synaptic has its own built in repo management tool, but is a bit basic.
There is the PyGtk version of the PyQt Software Sources tool software-properties-gtk, which if installed will replace Synaptic’s repo management tool, and also does create a menu entry. Both work here in Kubuntu 24.04, but I would not be surprised if this version exhibited the same symptoms you are seeing, though Ubuntu are more likley to actually support this version of their software better, since they use it themselves.
In any case, in the upcoming 25.10, the repos do show in Discover, and the button to open the Software Sources tool works there as well.
I would guess Kubuntu 25.04 has the same problems, but I can’t verify that at the moment, so I’ll say it is still borked there, considering the date that the packagekit devs fixed their apt-backend.
Any attempt to open software-properties-qt from Discover (whether via Driver Management or via Software Sources) fails with the previously described kdesu error. In my installation I can only get this dialog with “sudo software-properties-qt” (after su to an admin account). It fails to show the Mozilla deb repository (on any tab):
This shows only the Mozilla deb repository I installed via apt:
If you would enlighten me on how to install this, I would be glad to try it out.
If all else fails, I would consider upgrading to 25.10 when it comes out, although I am reluctant to leave the LTS path.
Many thanks for all your help!
sudo apt install software-properties-gtk or use Synaptic and search for this. But I suspect it likely will act the same as the Qt one, since these are identical other than using a slightly different GUI appearance.
Okay, you prbably need to replace the older .list file with the current .sources style of file.
ya, testing on 24.04, it works.
So, following Mozilla’s instructions will use the “old” .list file format in step #4, and so will most of the tutorials that have just copy-pasta’d this, so we can replace that with this:
echo "Types: deb
URIs: https://packages.mozilla.org/apt
Suites: mozilla
Components: main
Signed-By: /etc/apt/keyrings/packages.mozilla.org.asc" | sudo tee /etc/apt/sources.list.d/mozilla.sources > /dev/null
You will want to move /delete the original .list file from /etc/apt/sources.list.d, or rename it to /etc/apt/sources.list.d/whatever-name.list.save else you will get duplicate listing warnings.
Yes, GUI ways are harder imo, in this particular case until Ubuntu fixes their stuff.
It’s a bit of nitpick, but PyGtk referes to the python bindings to GTK2. GTK3/4 use a different naming called PyGObject.
Anyways, one thing I never liked about plasma discover in the 5.x series, was that it was tied down to appstream metadata and packagekit. So it for example on debian wouldn’t show graphical apps that exist like firefox-esr in the debian repos. I hope that plasma 6.x fixed this.
Nope, it relies on Packagkit for most everything just like it always has and Gnome Software does, so if Debian isn’t including metadata, it won’t show, but from my recollection, I don’t think the last releases of Plasma 5.27 had this issue so much, at least in *buntu. But I don’t think it is clear if this is actually a Packagekit or Appstream issue, as Discover one, or that the distro packaging is lacking.
Indeed, “sudo software-properties-gtk” delivers a similar dialog, but “System Settings - Driver Management” and “Discover - Software Sources” still yield the same kdesu error as before.
Replacing mozilla.list with mozilla.sources did enable software-properties-gtk to see the mozilla deb repository, as you predicted. Discover, however, still can’t see that I have Firefox installed.
Thanks again for your help!
That is a packaging thing (from Mozilla) I believe, not Discover itself.
That seems likely. I just installed GnuCash via apt and it shows up in Discover, while Firefox doesn’t. Interestingly, I no longer have Software Sources in Discover, presumably because I replaced software-properties-qt with software-properties-gtk.
P.S. Synaptic/apt offer me an upgrade to ubuntu-drivers-common, which neither Discover nor the KDE notification do.