Troubleshooting: Rmview showing a blank page

There is a common issue with rmview (when using the vnc version with RM software > 2.9): one might be able to connect to it but the viewer still will not show anything; the cursor pointer would work, but the updates on the screen would not show. There is no specific error signalling this issue: rmview would simply patiently wait for a signal from the tablet.

This problem has been documented in a number of issues: #111 #114 #133 #137

The root of the problem is that part of RM's custom authentication protocol (i.e. the initial handshake between rmview and the tablet) requires a certain ports to be open (port 5901, UDP protocol); this port is often closed by default in the presence of a firewall (on your computer). The transmission of the screen updates itself happens on port 5900, TCP protocol; this needs to be allowed by your firewall too. Note that your OS might be using a firewall even if you have not explicitly enabled it.

The solution is therefore to instruct your firewall to allow connections on 5901/UDP and 5900/TCP. Unfortunately there is no universal way of doing that, and the method will differ depending on your OS/firewall.

The following is a non-exhaustive list of methods that worked for people.

On Fedora

sudo firewall-cmd --add-port=5900/tcp # open the required TCP 5900 port
sudo firewall-cmd --add-port=5901/udp # open the required UDP 5901 port
sudo firewall-cmd --runtime-to-permanent # make the new firewall configuration persistent, so it applies also after reboot

On Ubuntu

sudo ufw allow 5900
sudo ufw allow 5901