Red Hat Enterprise Linux Troubleshooting Guide

Resolving the conflict

As you learned in the networking chapter, we can verify that a process has port 25 in use with a quick netstat command:

# netstat -nap | grep :25
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      1588/master         
tcp6       0      0 ::1:25                  :::*                    LISTEN      1588/master

When we run netstat as the root user and add the –p flag, the command will include the process ID and name of process for each LISTEN-ing socket. From this, we can see that port 25 is in fact being used and the process 1588 is the one listening.

To get a better understanding of what process this is, we can once again utilize the ps command:

# ps -elf | grep 1588
5 S root      1588     1  0  80   0 - 22924 ep_pol 13:53 ?        00:00:00 /usr/libexec/postfix/master -w
4 S postfix 1616 1588 0 80 0 - 22967 ep_pol ...