[SOLVED] AlmaLinux 9.1 Guest, black screen after login

[Mats62]

Hi. In the attached archive logFilesWithAndWithoutTheBlackScreenAfterLogin.zip are VBox logfiles, two copies each, from booting a VM and logging in to it. The files starting with an underscore are the same files as the ones without the "_", just with the most obvious parts of lines edited that will differ, due to timestamps, for slightly easier line-by-line comparison.

In one case I can log in, in the "broken case" it hangs with a black screen after I submit the password. (and I then forcefully power it off) If I wait a minute or so, before powering off, the login-screen comes back.

The difference between working and not working is one single line added in /etc/gdm/custom.conf in the guest:
[security]
#DisallowTCP=false
If I uncomment the line with "DisallowTCP=false I can no longer log in. (but if I set DisallowTCP to "true", I can also log in)

When the problem is present, /var/lib/gdm/.local/share/xorg/Xorg.0.log says "no screen found".

The same setting causes no issue on bare-metal installations with the same package-set.

The differences in the logfiles starting around line 1860 seem to be showing something, but I don't know what they are trying to tell me.

I'm not 100% sure, but it could be that this started to happen after a Win11 update to 23H2 on the host, the logs seem to suggest that the GAs are disturbed by that setting in custom.conf.

Any ideas?
thx in advance.... / Mats

[Lisa Miller]

Try to set the VGA Memory size of the VMs, to the same size which your real hardware have.

[agilis]

Hi Mat,

My installation of AlmaLinux's gdm.conf

Code: Select all

$ cat /etc/gdm/custom.conf 
# GDM configuration storage

[daemon]
# Uncomment the line below to force the login screen to use Xorg
#WaylandEnable=false

AutomaticLoginEnable=True
AutomaticLogin=rodev

[security]

[xdmcp]

[chooser]

[debug]
# Uncomment the line below to turn on debugging
#Enable=true

Perhaps that could help you? I don't know enough to help you troubleshoot further.

[Mats62]

Try to set the VGA Memory size of the VMs, to the same size which your real hardware have.

Thanks Lisa.

My VMs are created using textfiles so the Video Memory is always set to the recommended 128MB.

[Mats62]

Hi Mat,

My installation of AlmaLinux's gdm.conf

Code: Select all

$ cat /etc/gdm/custom.conf 
# GDM configuration storage

[daemon]
# Uncomment the line below to force the login screen to use Xorg
#WaylandEnable=false

AutomaticLoginEnable=True
AutomaticLogin=rodev

[security]

[xdmcp]

[chooser]

[debug]
# Uncomment the line below to turn on debugging
#Enable=true

Perhaps that could help you? I don't know enough to help you troubleshoot further.

Thanks agilis.
The issue I'm seeing does not make sense to me, I would have thought that TCP being allowed should not do any harm to the GA's ability to start the screen. (my hope with the post was that someone with more skills in that area may be able to interpret the VBox logs, maybe the GAs see the allowing of TCP as a security risk;-)

I have an easy-enough workaround in place, just comment the "offending line" so I'm not actively chasing this. (but would prefer to understand what it is) Will have a look at differences between your custom.conf and mine, and only after seeing yours here, I took note of the last line, maybe uncommenting the Enable=true in the [debug] section can reveals something.

[Mats62]

OK, turns out that the line "DisallowTCP=false" in /etc/gdm/custom.conf is only a problem when IPv6 is disabled. A new install which does not have IPv6 disable, does not have the issue. Will edit the original post to add "[SOLVED]".