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Years ago, I installed Kubuntu.
I used KDE a few years and installed (additionaly) Lubuntu-Desktop (sudo apt install lubuntu-desktop).
Because I like LXDE more than KDE, I tried to remove the existing KDE, by removing all KDE related stuff (with help of Synaptic).
Everthing was OK. Most of the KDE-Stuff was gone.

But everytime an Release-Upgrade is available (and installed), a lot of the KDE-Stuff will also be installed again.

How can I change this behaviour?
How to tell the Release-Upgrade that I use/want to have Lubuntu now?

EDIT:
When I try to remove kde-runtime via Synaptic, Synaptic would also like to remove ubuntu-release-upgrade-qt. I fear that I need this to upgrade to newer releases. Does each Ubuntu has it's own Upgrade-Process-Tool?

EDIT 2:
The general advice to do so, is to backup the personal files and to re-install the correct ubuntu version.

But, to be honest, where's the fun?
This seems like a nice 20 minute adventure.
(I don't want to give up my carefully, over years brought up, ubuntu. I will get rid of you KDE!)

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    Backup your personal files. To be honest, I think the easiest way is to make a fresh installation of Lubuntu and copy back your personal files. You can install the extra programs that you 'remember directly', and later on install programs when you need them. This way you will get rid of a lot of programs and libraries, that you will probably never use again.
    – sudodus
    Oct 18, 2017 at 18:34
  • OK, I feared that. I edited my question (I removed easy). So, do you know another way (beside re-installation)? I don't want to re-configure my system (at the moment).
    – Ben
    Oct 19, 2017 at 12:33
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    It is a known problem, that it is difficult to remove a desktop environment without causing damage to what you want to keep (in your case remove KDE and keep LXDE). You can backup everything (by using Clonezilla to make a compressed image of the whole drive) and after that take the risk, that the system breaks: Remove the meta package kubuntu-desktop. I don't know how much will be removed, and if something will be damaged, but it could stop the system from wanting to install the Kubuntu (KDE) stuff again. Maybe you need to identify and remove some other meta-package too.
    – sudodus
    Oct 19, 2017 at 12:40
  • I edited my question a little. Do you know if Lubuntu has it's own Upgrade-Tool?
    – Ben
    Oct 19, 2017 at 12:56
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    In my Xubuntu-Lubuntu combo I checked like this: dpkg -S /usr/bin/do-release-upgrade and it will reply ubuntu-release-upgrader-core: /usr/bin/do-release-upgrade so yes, the qt-tool you describe in the edited question is not used by Lubuntu. do-release-upgrade is used (and it comes with the package ubuntu-release-upgrader-core
    – sudodus
    Oct 19, 2017 at 13:03

2 Answers 2

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You've encountered one of the reasons it's difficult to fully convert Ubuntu from one DE (desktop environment) to another: dependencies. The request to remove ubuntu-release-upgrade-qt is most likely because it depends on something supplied by the kde-desktop meta-package (I'm guessing Synaptic package manager).

This is why it's almost always faster and easier to make a backup of the information you want to keep, and then do a clean install of a flavor you want to switch to. Doing so will also do a much better job of removing the space-consuming pieces of KDE that you no longer need, but don't know about (so can't remove manually).

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  • Yes, you're right. But where is the fun? I edited my question.
    – Ben
    Oct 19, 2017 at 13:30
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    Why won't you have fun re-creating your "carefully, over years brought up, ubuntu"? There's not really that much to configure in Lubuntu! Your lxpanel, your lubuntu-rc.xml, your menu.xml, pcmanfm settings. I've actually gone the other way: from Lubuntu to Kubuntu via a clean install :)
    – DK Bose
    Oct 19, 2017 at 13:46
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    @DKBose : This is my (home) development-pc. I want to avoid to re-configure MySQL, NodeJS, Mono, Wine, ApacheHTTP, Tomcat, nginx,Firewall, Network/VPN, various scripts modifcations (all over the system), Multi-Monitor-Setup, setup of Smartcard-Reader, Samba and so on...LXDE (with few modifications) is only a small part of it...I will give it a try...maybe I am lucky...
    – Ben
    Oct 19, 2017 at 16:15
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So, this an answer to my own question.

It seems to be possible to remove the KDE-Desktop environment (and maybe other desktop-environments), by removing everything which has something todo with (or references) KDE.

I realized this with help of synaptic package manager. I searched for packages (and references) containing following terms: kde, kubuntu, breeze, dolphin, plasma, phonon, libk and fully removed them (including all of it's dependencies!).

When it was not obviously KDE-related, I read the description of the package before.
Finally (after removing packages with synaptic), I called sudo apt autoremove from the console. This also removed many packages.

The whole process took me about 30 minutes to complete.

Conveniently, one day later, the 1710 upgrade was available. Best time to check if my changes would keep persistent or if the upgrade to 1710 will re-install KDE-Desktop (as each time before).

Result after upgrade to 1710:
The upgrade to 1710 did not install KDE-Desktop or any KDE related stuff again. I validated this via synaptic and my search terms.

So, I am happy. It worked for me. It was not that difficult and it was easier than re-install/re-configure my system.

Caution:
In my case, some fonts (which were used by LXDE) were removed. The result was, most of the labels, captions, buttons, window titles couldn't be usefully rendered anymore (characters were displayed as ?). So, it may be a little complicated to change the font settings in LXDE (when text is not readable).

tl;dr

  • seems to work, when removing (really!) all KDE related packages

  • may cause (strange/small/big) problems, due to removed dependencies (like fonts)!

Cheers!

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    Congratulations, you did it! But you have only been able to do it because you are an experienced user having an overview how the package-system works. A newcomer will be definitely overtaxed with this task and would end up easily with an unusable system. Remind that installing a new application could pull some KDE-related packages again (krita is an example). Most of us I guess would prefer a clean install. BTW, you should mark your own answer as accepted. Upvoted your answer for your effort, cheers.
    – mook765
    Oct 28, 2017 at 12:57
  • Congratulations and thanks for sharing your solution :-)
    – sudodus
    Oct 28, 2017 at 14:21
  • You are absolutely right, I would not recommend this for absolute unexperienced users (who fear or don't want to fight with their system). But if you want to re-install anyway (and want to gain some more experiences), why not, you can give it a try (save your data before!).
    – Ben
    Oct 28, 2017 at 14:31

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