Ubuntu 20.04 black screen with physical display

[Topnotchprincess]

Hello,

I have NoMachine 7.9.2 (Free) installed on both client and server side. Basic info:

Server – Ubuntu 20.04, Awesome WM, NVIDIA RTX 1080 Ti w Driver 460.91.03, Desktop w 2 physical monitors

Client – Ubuntu 20.04, Awesome WM, Laptop

Connecting using the NX protocol gets me a black screen. Server & client side logs attached.

Attachments:

1. NoMachine-log-2022.04.03-12.26.12.zip
2. nxdir.tar.gz

[fra81]

Hi,

are the 2 physical monitors turned on? How are they connected to the server (HDMI, Displayport…)?

From the logs it seems you are connecting to the server’s login screen. Do you still get a black screen if the server is logged on to the user’s desktop?

Can you try to disable hardware encoding as shown in https://knowledgebase.nomachine.com/DT11R00180#2.5?

[Topnotchprincess]

The monitors are connected via HDMI to one of the GPUs and are turned on. I am logged in to the same user account on the desktop.

I restarted the server after disabling hardware encoding, still get the black screen 🙁

[bucu]

@Topnotchprincess

Hi,

can you provide us the output of the “xrandr -q” command on server side? Have you tried lowering the screen resolution before connecting with NoMachine? Lastly – does Awesome WM supports scaling like @chiao has described?

[Topnotchprincess]

Thank you for your reply.

I have attached the xrandr output as well as my startup script that sets up the dual display. Lowering the resolution has no effect; I don’t think any decimal scaling is applied.

Interestingly, I was able to connect to my my laptop (Ubuntu 18.04 + Awesome WM) from my desktop. So the problem is either with

1. dual monitors

2. interaction between Ubuntu 20 / Awesome / NoMachine

I tested #1 by disconnecting one of the monitors but still got a black screen. Any suggestions?

[Britgirl]

To Topnotchprincess, submit those attachments from your earlier reply to forum[at]nomachine[dot]com. Thanks

[Topnotchprincess]

Sent.

[bucu]

Topnotchprincess

is the black screen present also with different WM?

For further investigation we would need a new set of logs from server side. Please make sure that you are connecting to the user’s session (not the login window one). You can follow this link to be sure you get all the logs.

[Topnotchprincess]

No black screen when connecting to Ubuntu/Unity desktop environments. Server side logs for a failed connection to Awesome WM are attached.

Please note that I used the same set of credentials to connect to both sessions (Unity & Awesome) – this is the same set I use to login to my desktop session.

Attachments:

1. NoMachine-log-2022.05.07-10.14.25.zip

[bucu]

Unfortunately logs you have sent are from login window not from a session using Awesome WM.
To get proper logs:
1. before connecting with NoMachine make sure that the user is logged in and Awesome WM is running
2. on server side execute: sudo /etc/NX/nxserver --debug --enable all
3. connect with NoMachine to server machine and make sure that the problem is reproduced.
4. on server machine execute: sudo /etc/NX/nxserver --debug --collect

You mentioned you have nvidia GPU. Is the problem present when using nouveau drivers? One more thing we noticed is that the “primary” output is disabled. Can you please remove your randr script and see if with default configuration you still get black screen?

[Topnotchprincess]

That is exactly what I did – I’ve been logged in throughout all of the above responses/attempts in this thread. The login screen issue might be pointing towards the problem – maybe something to do with the login manager and awesome?

I haven’t tried using nouveau – it’s likely not the cause since I can connect when logged into Gnome on the server. The issue sticks without the xrandr config script; even when I set one of the monitors as primary or use an alternate monitor config (eg mirror), the black screen persists.

What is the root cause of black screen – NoMachine not being able to detect a running graphical environment? How does NoMachine check that one is running?

[Topnotchprincess]

I’ve noticed that on my laptop where the server works well, it says ‘Desktop shared’ in the server status, however, on my desktop where it doesn’t work it says ‘Desktop not shared’. Therefore, there has to be something that’s preventing NoMachine from recognizing a running GUI.

[Topnotchprincess]

Just wanted to update that I solved the problem by disabling ubuntu’s display manager/gdm3. I login into a terminal and launch awesome wm using startx. My hypothesis was correct – the interaction between gdm and awesome wm must disable some key setting that allows NoMachine to recognize GUI.

[Britgirl]

the interaction between gdm and awesome wm must disable some key setting that allows NoMachine to recognize GUI.

We weren’t able to find out what because the logs we received were not sufficient and we have not been able to reproduce the problem either since our set-up in our labs correctly detects the display when Awesome is running there. We’ll consider this topic closed now that you have found a workaround.

 

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