I just wanted to chime in here. I have the same problem using 20.04. I was installed using the PPA, but I installed the deb package for 4.5.3 to see if it was working. I got the same results with the new package.
On the teacher or master side, I see
2021-02-27T18:26:47.768: [DEBUG] VncConnection::rfbClientLogDebug(): 0x7f25c1ffb700 ConnectClientToTcpAddr6: connect
2021-02-27T18:26:47.768: [DEBUG] VncConnection::rfbClientLogDebug(): 0x7f25c1ffb700 Unable to connect to VNC server
The student devices just say that the vnc server was started on 11100. No idea what is going on...
I’m not familiar with Veyon throughput or whether this is configurable. Generally I haven’t experienced performance issues using either Fullscreen demo or Window demo and though deselecting unused computers would achieve a modest performance gain my experience has been this doesn’t work very well on the fly. Since you are down to two lists I think it would be best to exit and restart Veyon whenever your selections change.
The VariantArrayMessage messages are interesting. They seem to indicate some kind of protocol incompatibility issue between master and client computers. Did you compile Veyon on your own on Linux Mint? If so, which version of Qt 5 is installed?
Regarding the screenshot warning: thanks for pointing that out! I just fixed the issue which will also be part of the upcoming 4.5.3 release.
@glew_ Monitoring/controlling student's computers at home is not possible. You would need to use VPN solutions to make the computers accessible in general and then also have the students install the Veyon Service – likely not feasible All I can suggest for the moment is to use meeting tools which allow students to share their screens.
Can you post a screenshot of the Master configuration page where you disabled some features? At a quick test I was unable to reproduce the behaviour you described.
Please note that you can't delete websites/programs that you configured statically in Veyon Configurator. Only custom websites/programs opened by teachers and added after checking the "Remember" checkbox can be removed afterwards using the delete key.
Currently you can only block Internet access completely using the Internet Access Control add-on. However it allows configuring exceptions (statically) such as local or intranet sites so these sites stay reachable while the Internet access is blocked. In a future release this year, we'll add a blacklisting features, so teachers can easily block the access to specific sites, e.g. video platforms.
You would probably have the default ACL applied which should by default permit all IPv4 inbound and outbound traffic.
Security groups are stateful so any outbound traffic sent from an instance is allowed a return response regardless of the inbound rules you have defined. Responses to allowed inbound traffic are also not blocked regardless of any outbound rules applied.
If you created and applied the security group then you will need to add the necessary inbound rules. By default this security group includes an outbound rule that permits all outgoing traffic.
The default security group allows all inbound traffic (and by default all outbound traffic) unless additional rules have been applied. If you are using the default security group I would suggest removing any added rules then attempting another demo connection to see if that works. I’m assuming the demo port is 11400.
Some technical background: first you should make sure the tray icon is visible on all computers. If it's not visible, the Veyon Service for some reason is not able to run it's own worker processes within the user session. The Veyon tray icon is provided by such a worker process. Launching the "Run program" or "Open website" features also launches a (different) worker process inside the user sessions as a helper process. This worker will then start the program or open the website and this way make sure the program or browser is opened with user privileges (instead of Admin/LocalSystem privileges which the Veyon Service is running with).
On computers where the tray icon is not visible, can you please check the VeyonServer.log file for messages starting with WindowsCoreFunctions and post them here?