How can I force all currently open sockets in linux to close from the command line?
Maybe it's easier to shut down a specific interface, for example:
to flush all your rules in the filter table
at this point all local sockets should be unavailable to a remote host if you have a redhat based os you should also use iptables -X to get rid of their custom chain for INPUT
if you want to the rules to remain on startup then you need to either include these in a script that runs in the /etc/rc.local file or use iptables save
This is all assuming that what you said you want to do is what you want to do.