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 13:53 ? 00:00:00 qmgr -l -t unix -u 4 S postfix 3504 1588 0 80 0 - 22950 ep_pol 20:36 ? 00:00:00 pickup...