GDM 3.28.3 and it's transition to GNOME Shell 3.28.4 in Ubuntu 18.04 - Q1

After systemd run the gdm service, I understand from Ubuntu Manpage that the

gdm starts an X server and runs a minimal GNOME session including a graphical greeter.

I found a diagram of the GDM’s process flow in GDM Documentation. It shows the Greeter as the starting process of the GDM.


  1. Am I correct to think the “X server” that is mentioned by Ubuntu Manpage preceeds the “GDM Greeter” that is mentioned in the GDM Documentation and it is not shown in the diagram? Or, does the “X server” process takes place at the “GdmGreeterServer” stage?

Appreciate your help to clarify my understanding. I had previously used Ubuntu’s Unity and am learning my ways around GNOME 3.

  1. According to the GNOME Display Manager v.3.26 Reference Manual, there is a mention of a GDM Face Browser. Is that the other name for the “User Chooser” that is mentioned in Q2?
  1. An example of the 1st graphical view of Ubuntu/GNOME3 after booting up is shown here. Is this window the “GDM Greeter”? If not, what is a “GDM Greeter”? I ask this because according to “Design notes for the Greeter” given in Design notes for the Greeter, the Greeter contains both a Boot Screen and a User Chooser. The 1st graphical view of Ubuntu that I had shown contains a “User Choser” but I did not see a GNOME boot screen before this. So does the Greeter have one or two GUI?

First of all: you should use a meaningful title for a topic and not open three different topics with the same title.

Additionally, this is not an Ubuntu forum; Ubuntu specific questions should go on the Ubuntu user support forum.

Finally: GDM and GNOME Shell 3.28 are releases from two years ago; GNOME 3.36 is going to be released in March. Since you’re using an LTS release of Ubuntu, you should really ask on the Ubuntu forums.

The X server, if at all necessary, is started as part of the greeter; in GNOME, the GDM greeter is literally GNOME Shell—started in a specific mode; this means that GNOME Shell will either try to run as a Wayland compositor, and thus not use X at all, or it will act as an X window manager, and will require starting the X server.

A “greeter” is any process that is started by GDM to perform the graphical side of asking the username and password, as well as the session to be started. In the case of GNOME, the “greeter” is a special session of GNOME Shell.

The rest of the documentation you’re referring to—including the “face browser”—is a remnant of GNOME 2, which means it’s not applicable to GNOME 3.

@ebassi Thank you for your reply. My original drafted post had contained 4 questions. However, as I am a new user here, the System had capped my post to contain a maximum of 2 hyperlinks. To express my questions, I had to resort to using a different post for each question. Furthermore, within a day I am capped to 3 posts, i.e. I could not post my 4th question.

So sorry for the inconvenience caused and thank you for merging my three posts into one. The System has also upgraded my trust level. Thanks.

Can you point me to more updated GNOME 3 documentation, specifically on GDM and GNOME Shell? I seem to be reading dated GNOME documentation according to your reply. I had got these GNOME references from GNOME’s website.

Thank you.

I’m not aware of any updated documentation on the GDM architecture in GNOME 3. Instead of having a greeter provided by GDM or by a third party, GNOME Shell is the greeter process; GDM spawns a (limited) user session, and on authentication success, it will launch your user’s session.

It’s probably easier for everyone involved if you ask a specific question. Alternatively, you could look in the GDM source tree.

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