linux命令正常运行时间的输出与命令nmap的输出不同

Question

In my linux box the command uptime tells me 800 days. However the command nmap says 48 days (in the Uptime line of its output). Should these 2 UPTIMEs be same? If not what each really means?

Answer 1

There is a reason why nmap prints Uptime guess . nmap detects the uptime by sending multiple consecutive SYN/ACK TCP and checks if there is timestamps option or a counter value, etc. Also the incremental rate may vary from OS to OS . Finally, some OS -es start the counter with a random value which complicates the uptime detection algorithm.

Best is to go and read the documentation on the topic on nmap 's webpage: Nmap: Remote OS Detection