gnome connections to running vnc server shows blank screen

[hansgoldenrod]

I've got Ubuntu 20.04.5 LTS, Gnome 3.36.8 running on an HP ProBook 4730s. I'm trying to remotely access it via my home network from a System76 machine running Pop!_OS 22.04 LTS.

On the HP machine:

1. Settings -> Sharing -> Screen Sharing, it is enabled and the check box for "Allow connections to control the screen" is checked. The same window says I should be able to connect to vnc://erik-HP-ProBook-4730s.local .

2. In terminal, I execute

sudo x11vnc -localhost -once -nopw -auth guess -find

and the output is

erik@erik-HP-ProBook-4730s:~$ sudo x11vnc -localhost -once -nopw -auth guess -find
[sudo] password for erik: 
03/11/2022 08:03:10 x11vnc version: 0.9.16 lastmod: 2019-01-05  pid: 32415
03/11/2022 08:03:10 
03/11/2022 08:03:10 wait_for_client: WAIT:cmd=FINDDISPLAY
03/11/2022 08:03:10 
03/11/2022 08:03:10 initialize_screen: fb_depth/fb_bpp/fb_Bpl 24/32/2560
03/11/2022 08:03:10 
03/11/2022 08:03:10 Autoprobing TCP port 
03/11/2022 08:03:10 Autoprobing selected TCP port 5900
03/11/2022 08:03:10 Autoprobing TCP6 port 
03/11/2022 08:03:10 Autoprobing selected TCP6 port 5900
03/11/2022 08:03:10 listen6: bind: Address already in use
03/11/2022 08:03:10 Not listening on IPv6 interface.
03/11/2022 08:03:10 

The VNC desktop is:      erik-HP-ProBook-4730s:0
PORT=5900

The output of

xauth list

is

erik@erik-HP-ProBook-4730s:~$ xauth list 
erik-HP-ProBook-4730s/unix:  MIT-MAGIC-COOKIE-1  6e9ed65843d0b5dda423d9be20e22b61
#ffff#6572696b2d48502d50726f426f6f6b2d3437333073#:  MIT-MAGIC-COOKIE-1  6e9ed65843d0b5dda423d9be20e22b61

On the System76 machine, I am using gnome connections. Sometimes it says "Unable to connect to HP-ProBook-4730s.local:5900: Error resolving "erik-HP-ProBook-4730s.local": Temporary failure in name resolution. Other times, it seems to connect, but the window is completely black. I am able to ping the ip address of the HP machine and it responds. I've also tried to connect to vnc://192.168.0.131:5900 and it says connection refused. I tried Remmina and it won't even connect.

Is there anything I am doing wrong? Why isn't this working?

I also looked through https://help.ubuntu.com/community/VNC/Servers and tried the Remmina tutorial.

[hansgoldenrod]

Removing the `-localhost` enabled me to see the port open up, using `nmap`. But x11vnc could not find the `display` no matter what I tried. Finally I gave up with x11vnc because it seems it is no longer supported and the Karl Runge website is offline. I switched to tigervnc and got it to work using `tigervnc-scraping-server` and `x0vncserver`.

[halogen2]

It's insecure to directly connect VNC. TigerVNC's scraping server has an option to listen on a Unix socket, which you can tunnel through SSH for a secure remote connection (I do this myself).

Here's the command I use to start TigerVNC scraping server -

X0tigervnc -display <display> -localhost -rfbport -1 -rfbunixpath </path/to/unix/socket/file> -SecurityTypes None -RawKeyboard

Replace the red parts with relevant values for your system. Refer to man X0tigervnc for more info on the above command and options.

Refer to man ssh for how to use -L option of ssh for tunneling.