Linux – WITHOUT using network command lines in linux, how to know list of open ports and the process that owns them

netstat

There's a process there, your userid just isn't privy to seeing what it is. This is a layer of protection provided by lsof that's keeping you from seeing this. Simply re-run the command but prefix it using the sudo command instead.

$ sudo netstat -antlp | grep 45136

There's even a warning about this in the output of lsof at the top.

(Not all processes could be identified, non-owned process info will not be shown, you would have to be root to see it all.)

Example

$ netstat -antlp | grep 0:111
tcp        0      0 0.0.0.0:111       0.0.0.0:*     LISTEN      -                   

$ sudo netstat -antlp | grep 0:111
tcp        0      0 0.0.0.0:111       0.0.0.0:*     LISTEN      1248/rpcbind

ss

If you're not having any luck with netstat perhaps ss will do. You'll still need to use sudo, and the output can be a little bit more cryptic.

Example

$ ss -apn|grep :111
LISTEN     0      128         :::111             :::*     
LISTEN     0      128          *:111              *:*     

$ sudo ss -apn|grep :111
LISTEN     0      128         :::111             :::*      users:(("rpcbind",1248,11))
LISTEN     0      128          *:111              *:*      users:(("rpcbind",1248,8))

Process ID still not there?

There are instances where there simply isn't a PID associated to the TCP port in use. You can read about NFS, in @derobert's answer, which is one of them. There are others. I have instances where I'm using ssh tunnels to connect back to services such as IMAP. These are showing up without a process ID too.

In any case you can use a more verbose form of netstat which might shed additional light on what process is ultimately using a TCP port.

$ netstat --program --numeric-hosts --numeric-ports --extend

Example

$ netstat --program --numeric-hosts --numeric-ports --extend |grep -- '-' | head -10
Proto Recv-Q Send-Q Local Address               Foreign Address             State       User       Inode      PID/Program name   
tcp        0      0 192.168.1.103:936           192.168.1.3:60526           ESTABLISHED root       160024310  -                   
tcp        0      0 192.168.1.1:2049            192.168.1.3:841             ESTABLISHED sam        159941218  -                   
tcp        0      0 127.0.0.1:143               127.0.0.1:57443             ESTABLISHED dovecot    152567794  13093/imap-login    
tcp        0      0 192.168.1.103:739           192.168.1.3:2049            ESTABLISHED root       160023970  -                   
tcp        0      0 192.168.1.103:34013         192.168.1.3:111             TIME_WAIT   root       0          -                   
tcp        0      0 127.0.0.1:46110             127.0.0.1:783               TIME_WAIT   root       0          -                   
tcp        0      0 192.168.1.102:54891         107.14.166.17:110           TIME_WAIT   root       0          -                   
tcp        0      0 127.0.0.1:25                127.0.0.1:36565             TIME_WAIT   root       0          -                   
tcp        0      0 192.168.1.1:2049            192.168.1.6:798             ESTABLISHED tammy      152555007  -             

If you notice the output includes INODES so we could back track into the process using this info.

$ find -inum 152555007

Which will show you a file which might lead you to a process.

References

• Port to PID

Because of the way the mount point gets hidden with umount -l, there is no way to find which processes are still using affected files.

The only way to get the list is to use lsof before umount -l to grep the relevant path. Example: lsof | grep "/mountPoint/".

If you want, you can take that output to extract the PIDs and continue monitoring them.