Display managers and desktop sessions

The display manager: the graphical login screen, which service starts it, and how a machine is switched between booting to a desktop and booting to a text console.

Lesson 2 of 3 in objective 106. User interfaces and desktops, part of LPIC-1 Exam 102-500.

A display manager is an ordinary service, pulled in by one target. In order: graphical.target (multi-user.target boots to a text console instead), then Display manager (GDM, SDDM, LightDM, XDM — start it with systemctl), then Login screen (authenticates, then starts a session), then Your desktop session. graphical.target multi-user.target boots to a text console instead Display manager GDM, SDDM, LightDM, XDM — start it with systemctl Login screen authenticates, then starts a session Your desktop session
A display manager is an ordinary service, pulled in by one target.

What a display manager is

A display manager presents the graphical login, authenticates the user and starts their session. XDM is the original and minimal one; GDM belongs to GNOME, SDDM to KDE Plasma, and LightDM is the desktop-neutral one. They differ in appearance and configuration file, not in job, and each keeps its configuration under /etc — /etc/gdm3/, /etc/lightdm/lightdm.conf and so on.

On a systemd machine the display manager is an ordinary service, so it is started, stopped and enabled with systemctl like anything else, and graphical.target is what pulls it in. Switching a machine to boot to a text console is systemctl set-default multi-user.target, and switching it back is graphical.target — the modern spelling of changing the default runlevel between 3 and 5.

The command that decides whether a machine comes up at a login screen or a text console. systemctl set-default multi-user.target — part 1, systemctl: The same tool that starts, stops and enables the display manager; part 2, set-default: Changes which target the machine boots to by default; part 3, multi-user.target: Text console, the old runlevel 3; graphical.target is 5. 1 systemctl 2 set-default 3 multi-user.target 1 The same tool that starts, stops and enables the display manager 2 Changes which target the machine boots to by default 3 Text console, the old runlevel 3; graphical.target is 5
The command that decides whether a machine comes up at a login screen or a text console.

Worth carrying in

XDM / GDM / SDDM / LightDM
Display managers: neutral, GNOME, KDE Plasma, and desktop-neutral.
graphical.target
The systemd target that pulls in a display manager.
systemctl set-default multi-user.target
Boot to a text console instead of a desktop.
systemctl stop gdm
A display manager is just a service.

What the exam does with this

Objective
106. User interfaces and desktops
Share of the exam
6.67% (the whole objective)
Questions in this lesson
6
Signed for by a person
0

Partly checked. None of the 6 questions here has been read against the cited source by a person. 6 questions have been checked against their cited clause by an automated pass — which is not the same thing, and is not a signature.

Only questions a person has signed for are used in mock exams here. That is the whole difference between the two kinds of checking above.

How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.

Drill this lesson

A lesson is one sitting: the trainer draws a short run from these questions alone and spaces the ones you get wrong.

Practise Display managers and desktop sessions

Questions in this lesson

Practise Display managers and desktop sessions

The rest of objective 106