OS is just Kernel and Shell which work hand in hand. The distribution (distro) is a combination of a customized shell(s) working on a kernel. This means, for example, Kali, Ubuntu, Fedora, Mint, etc are different distros that work on Linux kernel. The shell acts as an interface between the user and the kernel.
GNU is an Operative System. You can use this operative system with a different kernel such as Linux kernel, Hurd kernel, Darwin kernel, etc.
The windowing system is just the basic layer for a GUI environment. Every Linux distribution is a GNU operative system with a Linux kernel and a windowing system (X Window System is common on Unix like systems).
A window manager is system software that controls the placement and appearance of windows within a windowing system in a graphical user interface. Most window managers are designed to help provide a desktop environment (An X window manager is a window manager that runs on top of the X Window System)
In the case of X or Wayland Window System, the shell consists of an
X window manageror a
Wayland compositor, respectively, as well as of one or multiple programs providing the functionality to start installed applications, to manage open windows and virtual desktops, and often to support a widget engine.
GNOME Display Manager (
GDM) is a display manager (a graphical login manager) for the X11 windowing system that lets you easily use your system. The X protocol has been at version 11 (hence "X11")
Ubuntu GDM uses the gdm3, which is the default GNOME 3.x desktop environment greeter in Ubuntu 17.
However, there are still a few pain points that simply couldn't be overcome for
Ubuntu 20.04.2 LTS (Focal Fossa) (certain video card manufacturers stand out). Migrating everybody to Wayland in the 20.04 cycle would cause too many folks' systems to break.
If you face a login loop after changing
Ubuntu with Wayland to
Ubuntu, one of the solutions is to change the default display manager from
lightdm through the following steps:
naser@cairo:~/$ sudo apt-get install lightdm -y
naser@cairo:~/$ sudo reboot
Note: You may find that Screen lock disabled on the Ubuntu +20 flavors
Incredible resources on the internet though, so be sure to share what you can't live without in the comments.