Upgrade from KUbuntu-16.04 to Ubuntu-18.04

Question

Currently I'm running KUbuntu-16.04 with KDE, however, I would like to upgrade to the default Ubuntu-18.04, with the default Ubuntu.

My pc is a efi duaboot with windows 10 and KUbuntu. I would like to have KUbuntu completely removed and Ubuntu 18.04 fully, not the minimal but with the default distribution installed.

For the current users I'would like to keep their homefolders, so any documents and programs shouldn't be removed in their homefolders shouldn't be touched.

Would this work if I only update the /etc/apt/sources.list?

Any advise is very welcome

best regards, hetepeperfan

Possible duplicate of How to upgrage Ubuntu on a dual boot system? — newcat1000, Jan 07 '19 at 12:35
Is their any specific reason to completely remove Kubuntu other than upgarding and switching to default Ubuntu? Since Kubuntu can be updated to 18.04 and then its default desktop environment can be change to make it regular Ubuntu. — Kulfy, Jan 07 '19 at 15:33
@Kulfy I would like to remove what I do not use. I prefer to switch to the default gnome environment. Otherwise I might end up with okular (kde) opening .pdf's instead of evince (gnome) and that kind of problems. — hetepeperfan, Jan 07 '19 at 17:14
The problem is probably mostly that I do not precisely know all of which packages to remove that relate to kde. — hetepeperfan, Jan 07 '19 at 17:17

score 2 · Accepted Answer · answered Jan 10 '19 at 23:09

The sources.list file is a key factor in adding or upgrading applications to your Ubuntu installation. This is also used by your system for system updates. The sources.list should only be edited if you know what are you doing otherwise that would create problems in updating Ubuntu. The official flavors of Ubuntu (ordinary Ubuntu, Kubuntu, Xubuntu, etc.) uses the same repository. They only differ in their default desktop environment, for example, Ubuntu uses Unity or GNOME (17.04+), Kubuntu uses KDE Plasma, Xubuntu uses Xfce. So, it is pointless to edit sources.list to switch to Ubuntu 18.04. You might also like to read Is editing sources.list a good idea?

So, upgrading and switching can be done in two ways:

Updating Kubuntu and switching default desktop environment:
- Upgrade Kubuntu 16.04 to 18.04 using:
```
do-release-upgrade
```
- Install GNOME and gdm3:
```
sudo apt install ubuntu-desktop gnome-shell gdm3
```
- Choose gdm3 as default and reboot system.
- You'll be welcomed by GDM. Choose Ubuntu as your desktop environment.
- Welcome to the "default Ubuntu".
- If you want you can remove the Kubuntu's default desktop environment and display manager too. Kubuntu uses plasma-desktop and sddm.
```
sudo apt autoremove plasma* sddm
```
- The default apps (like evince) will be installed automatically with Ubuntu Desktop.
- Remove some more KDE related packages:
```
sudo apt autoremove kde* qml-module-org-kde* libkf5kdelibs4support* libkf5libkdepim* software-properties-kde xdg-desktop-portal-kde libkde* konsole
```
- I've tested this on Virtualbox and side by side compared the packages. There are other packages left like KCalc, KDE Partition, etc. Although they don't take much space but can be removed manually and easily.
- I'll personally prefer this method. Hassle free and no chance of losing any file.

Clean Install of Ubuntu 18.04:
- In this method you need to have a backup of all user files on some other drive/partition.
- Create users again and restore their home folders.

Upgrade from KUbuntu-16.04 to Ubuntu-18.04

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