GDM doesn't start Xorg with `-listen tcp` when DisallowTCP=false is set in custom.conf

[Thomas Debesse]

GDM doesn't start Xorg with `-listen tcp` when DisallowTCP=false is set in /etc/gdm3/custom.conf

Nine years ago with xorg-server 1.17 ago the `-nolisten tcp` option was reversed as a `-listen tcp`.

Before, the behavior was to always enable tcp unless `-nolisten tcp` was set, now the behavior is to always disable tcp unless `-listen tcp` is set.

To reverse the behaviour, GDM should be built with `HAVE_XSERVER_WITH_LISTEN` being defined, typically by passing `-DHAVE_XSERVER_WITH_LISTEN=1` to the compiler, as seen in the source:

https://gitlab.gnome.org/GNOME/gdm/-/blob/08aea8002a2725f07a0889f52584d284648b2e82/daemon/gdm-server.c#L329

GDM modified its behaviour 8 years ago:

https://gitlab.gnome.org/GNOME/gdm/-/commit/3f59fa0da5168451898db63e51e312ce894af0c1

and two years ago it was modified again:

https://gitlab.gnome.org/GNOME/gdm/-/commit/bc16c9898012e463bc6b79c3faa8f81ed54527f7

Maybe this define was never added to the GDM build script?

The web is full of forum threads of people trying to make GDM works with TCP listening, fail to get it working, and give up and use lightdm instead, this is probably because GDM was built without the expected define.

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: gdm3 46.0-2ubuntu1
ProcVersionSignature: Ubuntu 6.8.0-44.44-generic 6.8.12
Uname: Linux 6.8.0-44-generic x86_64
ApportVersion: 2.28.1-0ubuntu3.1
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: GNOME
Date: Tue Oct 1 10:43:26 2024
RebootRequiredPkgs: Error: path contained symlinks.
SourcePackage: gdm3
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.default.apport: [modified]
mtime.conffile..etc.default.apport: 2018-06-16T17:39:00.798346
mtime.conffile..etc.gdm3.custom.conf: 2024-10-01T10:43:20.322306