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I am learning about Graphical User Interfaces in Ubuntu and constantly come across different terms, which cause a lot of confusion for me. I have tried reading easy-to-understand tutorials about the relationship between the named packages, but I don't have a complete picture.

LightDM appears as a service on my installation and is a 'Window Manager', how is this related to Compiz, which is also a Window Manager but not a service? Is Metacity also a Window Manager?

Then there comes Gnome 3, Unity, Gnome Shell and Gnome - all of which seem to be different things. Please help me understand the relationship between all this terminology.

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1 Answer

up vote 22 down vote accepted

You only need to know 4 terms:

  • Display manager
  • Window Manager
  • Graphical User Interfaces (GUI)
  • Desktop Environments

Display manager

Are LightDM, GDM, KDM, LXDM. They normally has desktop manager somewhere in their names. These are the ones that start the xserver at boot and provide, normally, a login screen.

Window Manager

Compiz, Metacity, Mutter, W9dk, fluxbox, etc. are window managers. These are too many to do a list. If you want you can check all the packages that provides x-window-manager to get a incomplete list of the window manager in Ubuntu. These only are responsible of drawing the application borders, managing the position of the windows, themes and decorations.

Grapical User Interfaces (GUI)

Anything that the user interacts in any graphical way, with icons and representations. Window Managers, Display Manager and Graphical shells, applications, etc. falls in this category. Whatever the user is using that is represented predominantly in a graphical way is a GUI.

Desktop Environments

In the Linux world, it's referred as a set of applications, packages, services, etc. that provides a complete and balanced ecosystem for the user. Unlike Window Manager or Desktop Manager, Desktop Environments take care of everything. From the login screen through your mail application, the network manager, text editor, the system settings, image viewer, file manager, etc. There are only 4 well knows Desktop Environments in Linux and Ubuntu:

  • GNOME
  • KDE Desktop Environment
  • LXDE: Lightweight X11 Desktop Environment
  • XFCE Desktop Environment

These have a complete set of applications, settings, services, desktop/file/window managers, internet browser, etc.


So, to address your specifics concerns:

LightDM appears as a service on my installation and is a 'Window Manager'

False, LightDM is a Display Manager.

how is this related to Compiz, which is also a Window Manager but not a service?

Have nothing in common. Both have different functions. Compiz is a window composer, window decorator, a window manager.

Is Metacity also a Window Manager?

Yes.

Then there comes Gnome 3, Unity, Gnome Shell and Gnome - all of which seem to be different things.

Gnome 3, Gnome Shell and Gnome are the same thing, being practical. Unity is totally different. Unity is another shell opposed to Gnome/3/Shell. Gnome 3 Shell has been commonly called as Gnome Shell in the past, right now saying GNOME, GNOME 3 Desktop Environment or Gnome Shell carry the same meaning.

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Thanks! When I browse through the gconf database, however, I find an entry for /desktop/gnome. However, as far as I know I am using Unity on Ubuntu 12.04. Why then, does gnome exist in the database? –  jesterII Jan 26 at 21:42
    
@jesterII Unity is a shell which use Compiz/Gnome. –  Braiam Jan 26 at 21:47
    
Then how come comparisons between Unity and GNOME 3 Shell make sense, if Unity is a shell that uses Gnome? –  jesterII Jan 26 at 23:54
1  
I am not doubting your answer, I am asking follow-up questions to help resolve my confusion. –  jesterII Jan 27 at 0:15
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@jesterII each question should be searchable and answerable by all the community. You can reference this answer with your new question so the whole community know from where you are coming from. If you don't have any doubt about this answer and your question is just a follow up then ask a new question. –  Braiam Jan 27 at 0:17
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