Steps to reproduce the issue:
1) Go to Webmin -> Webmin -> Usermin Configuration 2) Click on Port and Addresses 3) Change port from 20000 to other port let's say 50000 and click Save
Load a browser and access Usermin on port 50000. It is not working. Let's check iptables in Linux Firewall. There is no rule for accepting on port 50000. This is a bug, or you have to inform you Webmin admins once they change Usermin port, they have to change the port number in IPTables.
Related to this I have some remarks to do:
1) Changing Webmin port it is working great, this behavior should be the same for Usermin too. Why do you create a port range in firewall? I changed the port to 40000 and I see there is a range of ports 4000:40010 as a new rule. Why not only one port, 4000 and not a range?
2) I do recommend one someone is changing a port for Webmin/Usermin to delete or change the previous rule related to their ports. Even I change the ports for Webmin/Usermin I still have the default ports open 10000 and 20000. It is not a big issue, but it could be done automatically.