I Got The File - 'fuser' Got the Process(es)

We can also check open files the other way around, i.e. - given a file, which
process currently hold it open. For example:

 # fuser -v /usr/bin/telnet 

                      USER        PID ACCESS COMMAND
 /usr/bin/telnet      choo       1100 ...e.  telnet

The 'fuser' command allows you also to see which processes keep a certain TCP or UDP port open - read the man page for more info.