This guide has been tested on a fresh installation of Ubuntu 20.04.3 LTS (Focal Fossa)
1. aptitude vs apt/apt-get
We'll be using aptitude, because its ability of suggesting multiple solutions to package conflicts can make newbies less likely to break their systems.
(1) Make sure your packages are up to date:
# apt update && apt full-upgrade
Reboot if necessary.
(2) Install aptitude:
# apt install aptitude
2. Select and install KDE packages
These packages below are meta-packages -- they depend upon other, "real", packages, and with their installation they pull them in.
kde-plasma-desktop -- Bare-minimum installation. Including basic utilities like a file manager, browser, and terminal emulator.
kde-standard -- Everything in kde-plasma-desktop with a standard suit of system utilities (for example, calculator, email, media player, and advanced text editor)
kde-full -- Everything in kde-standard with extra system utilities, games, and educational applications.
(1) Install kde-standard:
# aptitude install kde-standard
(2) Configure SDDM:
You'll be asked to choose between gdm3 and sddm. Select sddm. gdm3 is for GNOME and sddm is for KDE.
3. Purge GNOME
Users can switch between "Plasma" (for KDE) and "Ubuntu" (for GNOME) from the login screen. However, errors will begin to pop-up when switching to GNOME this way, probably because configuration files are altered for KDE.
So, whether you're going to stick to KDE, or you're gonna switch back to GNOME with no errors popping-up, you'll want to completely remove GNOME and its configuration files first.
(1) Purge gnome-shell and autoremove associated packages:
# aptitude purge gnome-shell
During the process, aptitude will detect some unmet dependencies caused by this removal, and will propose a few solutions. The first solution is good enough, just type Y for yes.
(2) Purge previously only removed packages:
# aptitude purge ~c
4. Other packages
(1) Friendly fire
Some packages, like Firefox, will also get purged in the process above 'cause they depend on GNOME dependencies. But worry not. Reinstalling them won't require you to install an entire GNOME Desktop Environment.
# aptitude install firefox
(2) Extra KDE packages
Let's say that you've installed kde-standard, and you want all those fancy productivity features from packages of kde-full. Just check out their related packages:
And get after it:
# aptitude install kdeadmin kdegraphics kdemultimedia kdenetwork kdepim kdeutils kdeaccessibility kdesdk kdewebdev
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