Port scanner on Linux


nmap ip


-A: enable OS detection and version detection
-oN/oX filename: output scan in normal, XML format
-n: no reverse DNS resolution
-p[ports]: only scan specified ports
-f: fast mode, fewer ports
-sP: only ping scan
-sS/sT: TCP SYN/Connect() scans
-sU: UDP scan

Empty a file without deleting and recreating commands


echo > filename