find out what your linux server public IP adress is code example
Example: how to find public ip address in linux
$ wget -qO- http://ipecho.net/plain | xargs echo
$ wget -qO - icanhazip.com
120.88.41.175
$ wget -qO- http://ipecho.net/plain | xargs echo
$ wget -qO - icanhazip.com
120.88.41.175