Description of problem:

According to the documentation[1],

By default, GDM will install desktop files in the <share>/xsessions
directory. GDM will search the following directories in this order
to find desktop files: <etc>/X11/sessions/, <dmconfdir>/Sessions,
<share>/xsessions, and <share>/gdm/BuiltInSessions. By default the
<dmconfdir> is set to <etc>/dm/ unless GDM is configured to use a
different directory via the "--with-dmconfdir" option.

A session can be disabled by editing the desktop file and adding a
line as follows: Hidden=true.

So it should be possible to hide an installed session (e.g. gnome-session) by
doing creating an overriding file at /etc/dm/Sessions/ or /etc/X11/sessions/.

1. https://help.gnome.org/admin/gdm/stable/configuration.html.en#sessionconfig

Version-Release number of selected component (if applicable):

gdm-3.28.2 and later (happens on RHEL 7, 8 and 9)

How reproducible:

Always

Steps to Reproduce:

1. Create overriding files for the Standard session:

1. mkdir -p /etc/dm/Sessions/ /etc/X11/sessions/
2. ( cat /usr/share/wayland-sessions/gnome.desktop; echo Hidden=true ) > \
   /etc/dm/Sessions/gnome.desktop
3. ( cat /usr/share/xsessions/gnome.desktop; echo Hidden=true ) > \
   /etc/X11/sessions/gnome.desktop
4. ( cat /usr/share/xsessions/gnome-xorg.desktop; echo Hidden=true ) > \
   /etc/X11/sessions/gnome-xorg.desktop

2. Restart gdm

1. systemctl restart gdm.service

3. Choose a user in the greeter screen and click on the cogwheel.

Actual results:

The "Standard (Wayland display server)" and "Standard (X11 display server) on
Xorg" options are still shown.

Expected results:

The "Standard (Wayland display server)" and "Standard (X11 display server) on
Xorg" options should not be shown.

Additional info:

A fix is already available upstream:

https://gitlab.gnome.org/GNOME/gdm/-/merge_requests/202

/usr/share/xsessions/gnome.desktop and /usr/share/xsessions/gnome-xorg.desktop
are reduntant. One of them should not exist.

Currently the only workaround is to remove the existing session files or append
"Hidden=true" to them:

1. echo Hidden=true >> /usr/share/wayland-sessions/gnome.desktop
2. echo Hidden=true >> /usr/share/xsessions/gnome.desktop
3. echo Hidden=true >> /usr/share/xsessions/gnome-xorg.desktop
4. systemctl restart gdm

But this does not survive a re-installation of gnome-session-xsession and/or
gnome-session-wayland-session.

The directory names are confusing:

/etc/dm/Sessions/ -> Wayland sessions
/etc/X11/sessions/ -> Xorg sessions

A fix is required on RHEL 9 too. It would be desirable to have a fix for RHEL 7
also, since customers frequently ask for ways to disable either the Standard
or the Classic session.