Network port open, but no process attached?

Solution 1:

Have you run netstat and lsof as root or with sudo? Notice the last column:

netstat -ln --program
tcp        0      0 192.168.21.1:53         0.0.0.0:*               LISTEN      -               
tcp        0      0 127.0.0.1:53            0.0.0.0:*               LISTEN      -               
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      -

sudo netstat -ln --program
tcp        0      0 192.168.21.1:53         0.0.0.0:*               LISTEN      2566/named      
tcp        0      0 127.0.0.1:53            0.0.0.0:*               LISTEN      2566/named      
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      3125/sshd

From the netstat manpage:

You will also need superuser privileges to see this information on sockets you don’t own.

How do you know there isn't one running? If the port is in use it makes sense that it would exit immediately with a 'socket in use' error. what happens when you telnet to the port?

telnet localhost 5666

Solution 2:

Ports open by the kernel won't show up with program name. Some NFS and OCFS stuff come to mind. Maybe it's something like that?

Or it could be a kernel bug. Check kernel logs for OOPS and BUG.

---

Solution 3:

execute 'netstat --tcp --udp --listening --program' as root user. other wise you it won't give PID/Program Name

then use kill -9 PID command

---

Solution 4:

I actually wrote a small shell script to help id these occassional questions:

#! /bin/bash
([ "$1" = "" ] || [ "$2" = "" ]) && echo "Usage: tracer <space> <port>" && exit 0
for i in `fuser -n $1 $2`
 do
  ps aux | grep $i | grep -v 'grep'
 done

save as /usr/local/bin/tracer; output:

root@mo-log:/usr/flows# tracer tcp 80
80/tcp:             
root     27904  0.0  0.0 111668  3292 ?        Ss   Aug04   0:03 /usr/sbin/apache2 -k start
www-data 32324  0.0  0.0 335332  3560 ?        Sl   Aug05   0:00 /usr/sbin/apache2 -k start
www-data 32327  0.0  0.0 335324  3560 ?        Sl   Aug05   0:00 /usr/sbin/apache2 -k start

You will need root privileges to use it

---

Solution 5:

I was able to track down the process by getting its inode via netstat and then using that inode with lsof. See my more detailed answer in https://serverfault.com/a/847910/94376.