When I use the -p or --processes option, I get the output like this:

LISTEN   0   511   ...   ...   users:(("nginx",4209,255),("nginx",18819,255))

I know ("nginx",4209,255) means the nginx process with pid 4209 is using the socket, but what is the meaning of 255, what does it stand for?

I looked up in manuals but didn't find the answer.


That's file number descriptor. You can read these line from source code to see it.

On Debian system, you will get a better output:

tcp    ESTAB      0      0   ...      ...    users:(("skype",pid=3074,fd=67))

Base on your output, I guess you're on a Redhat or Ubuntu base systems.

  • Cuong, Ubuntu also does not show fd in front.. – heemayl Oct 30 '15 at 10:11
  • 1
    @heemayl: Yes, I also checked with Linux Mint. It seems that Redhat base and Ubuntu base don't show it. – cuonglm Oct 30 '15 at 10:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.