Why network port is open but no process attached?（為什麼端口被打開，但是沒有程序号）

When I check my system today, I noticed a weird output from netstat’s output,

There is no process attached to an open port. I used different command to try to address the process that attaches to this port, but all failed.

After searching around, I realized it’s an port opened by kernel, that’s why it won’t show up with program name. For the port like this, it may relate to NFS and OCFS stuff, or something like that, or it could be a kernel bug.  If you need to find more details, check kernel logs for OOPS and bug.

A nmap scan help me confirm my guess,

Nmap finished: 1 IP address (1 host up) scanned in 6.154 seconds