I am surprised that there have been no updates to the webmin interface to support the new samba version (that has been rolled out to most major linux distros now) -- am I the only one that has been using webmin to do my admin on samba servers ? I think NOT...
Anyway - here is a quick and dirty fix to the start/stop entries in the webmin samba module to correct it for Version 4:
Command to stop Samba servers
service smbd stop && service nmbd stop
Command to start Samba servers
service smbd start && service nmbd start
Command to restart Samba servers
service smbd restart && service nmbd restart
Of course for manual use - you'll need to add in a "sudo" as follows:
sudo service smbd restart && sudo service nmbd restart
There are other issues that I have not sorted out, like for example the command that was previously available called /usr/bin/smbgroupedit appears to have gone away in version 4. Anyway - I will update here if I get any more feedback on this, as I would think this is a very commonly used module. Feel free to comment here if you have any additional data.