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Description of problem:
Not able to configure X server to listen for TCP connection from the remote host.
Edit /etc/gdm/custom.conf file and set DisallowTCP=false in [security] section:
~~~
# GDM configuration storage
[daemon]
# Uncomment the line below to force the login screen to use Xorg
WaylandEnable=false
[security]
DisallowTCP=false <<<====
[xdmcp]
[chooser]
[debug]
# Uncomment the line below to turn on debugging
#Enable=true
~~~
The X server keeps blocking the network connections.
Version-Release number of selected component (if applicable):
gdm-40.0-15.el8.x86_64
How reproducible:
Always
Steps to Reproduce:
1. Configure the /etc/gdm/custom.conf file with "DisallowTCP=false" option
2. Restart gdm or system
Actual results:
X server keeps blocking tcp connection from the remote hosts
~~~
# ps aux | grep X
gdm 2742 0.0 4.7 996512 63472 tty1 Sl+ 07:51 0:00 /usr/libexec/Xorg vt1 -displayfd 3 -auth /run/user/42/gdm/Xauthority -nolisten tcp -background none -noreset -keeptty -novtswitch -verbose 7 -core
~~~
Expected results:
X server should allow network connection when DisallowTCP=false option is configured in the /etc/gdm/custom.conf file.
Additional info:
Comment 1Ray Strode [halfline]
2021-11-23 15:23:23 UTC
Raising the Customer Escalation flag, per RME EN-50824 and the business impact provided by the customer,
Business impact:
We have 2000+ Red Hat desktops in our private environment. Several mission critical applications are unable to launch for our environment, making it impossible for our users to do their jobs.
We have custom X applications that rely on being able to present remotely to the desktop over the X ports (60xx). We received a bug fix for GDM that actually fixes the ability to *turn on* the port, but now have a bug in the Xorg server that breaks the desktop completely (Xorg will not load) when IPv6 is disabled (which it is in our environment.) We use nVidia video cards on all physical desktops and therefore cannot use Wayland. We currently cannot proceed in our 8.5 deployment because of the mission critical application block.
2 bugs have been filed on this: 2029202 against GDM which has been fixed, which then led to bug 2075132 against libXTrans, which has not been fixed. Until we get a build that allows TCP ports to listen appropriately on the Xorg server, we can't proceed with our 8.x rollout. We need a build that actually works properly with IPv6 disabled. Bug 2075132 has been marked as medium priority and medium severity, which seems completely off since it simply does not work at all with IPv6 disabled.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (gdm bug fix and enhancement update), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2022:1771
Comment 19Chandrakumar Muthaiah
2022-12-17 18:28:13 UTC
The below alternative approach seems to work, at least in Fedora 37, not sure about Red Hat Enterprise Linux 8.
The recent GDM does not honor the custom.conf file but instead you could use gdm-runtime-config with below command that enables -listen tcp
/usr/libexec/gdm-runtime-config set security DisallowTCP false