Home / ubuntu / Questions / 1497123
Accepted
Nicholas Saunders
Asked: 2023-12-15 21:48:25 +0800 CST

How to determine what's listening to port 25 on localhost?

  • 772

How do I determine what's running on port 25 below?

nicholas@mordor:~$ 
nicholas@mordor:~$ ss -tlpn sport 25
State                   Recv-Q                  Send-Q                                   Local Address:Port                                    Peer Address:Port                  Process                  
LISTEN                  0                       100                                          127.0.0.1:25                                           0.0.0.0:*                                              
LISTEN                  0                       100                                              [::1]:25                                              [::]:*                                              
nicholas@mordor:~$

Can I trace this using ps somehow?

In the context of:

where does fetchmail store mail?

command-line

1 Answers

  1. Best Answer

    You've passed the -p (--processes) flag to ss - but the Process column is empty because you don't have sufficient privileges. However

    sudo ss -tlpn sport 25

    should show something like users:(("master",pid=1546,fd=13)). Alternatively (again with elevated privileges)

    sudo lsof -i :25

    You can then interrogate using the PID from above ex.

    systemctl status <PID>

    or (if it is not a systemd service)

    ps -fp <PID>

    or for information about the process hierarchy if you have installed pstree

    pstree -s -p <PID>
    • 2