I have two PCs on the same LAN, both Debian 12 with KDE. I installed Krfb on one and Krdc on the other.

When I try to connect from the client, Krdc to the server Krfb, I get the popup on the server asking for permission to allow the connection. I confirm, and the client comes up again with the popup to enter the password, stating that "authentication failed". I tried Remmina as a client and same issue happen.

The two PCs don't have a firewall set up or any other security running. Running nmap against the server confirms that port 5900, the default for Krfb is listening. It should be a straightforward connection. The internet doesn't have much at all on something like this. Any ideas?

Works here... Are you using the right password? You're meant to use the one generated by KRFB, which shows in the window.

I did note that it doesn't work with blank/null passwords. You need to have a password in there.

Oh yes, I definitely used the exact password that Krfb generated, many times. Eventually I started experimenting with changing it but still no luck.

It's such a weird thing. Krdc sees the server right away when I start it, Krfb responds right away when I enter the password in Krdc, but then the connection just doesn't happen.

Are these physical machines or VMs?

2 physical machines next to each other.

I don't use Debian, and instead use tigervnc. Install that from the repo, something like apt get tigergvnc on both systems. You might also like to install a light windows manager, apt get jwm perhaps.

On one, run vncserver :1
that will prompt for a password that must be at least 6 characters, that has to be entered twice.

Immediately thereafter kill that
vncserver -kill :1
and edit the newly created ~/.vnc folders xstartup to change the last line from twm to jwm (or whatever window manager).

Restart vncserver, but with no security
vncserver :1 -SecurityTypes none


On the same box, connect to that. vnc adds 5900 to whatever Display number you allocated, so 5901 in this case
vncviewer localhost:5901
and it should drop straight into a jwm windows desktop

From the other box I more usually set up a ssh tunnel
ssh -f -N -L 5900:localhost:5901 <ip of server>
and then run
vncviewer localhost

Going through the above might help to identify where the problem lay with your current setup/choice.

Just an update if anyone else has the same problem. I got it to work, partially...

After following the instructions at https://wiki.debian.org/PipeWire I can finally use Krdc to vnc into the Krfb server. The problem is that the display of the remote server is garbled and can't be used.

I then used Remmina as a client and the display works perfectly. The mouse works, but the keyboard doesn't work. It's a KDE bug according to this post: https://bugs.kde.org/show_bug.cgi?id=435338

Until Krfb is fixed, I'm experimenting with x11vnc.


EDIT: I just installed Gnome and removed KDE on the server. Gnome works fine with x11vnc and now I can remote without a single issue.