Linux/Unix : fatal: the Postfix mail system is already running

Problem :

Postfix throws out this error message :

fatal: the Postfix mail system is already running

when attempting to start postfix service. The strange thing is that the postfix daemon is not running. You can find out if the postfix service is running or not by issuing this command :

>service postfix status

postfix is not running.

Solution :

Chances are that the postfix's PID file was not deleted during previous shutdown or because of some other reason. Navigate to /var/spool/postfix/pid and remove the master.pid file.

Start the service again :

>service postfix start

and if every goes smoothly, it should produce this message :

Starting Postfix Mail Transport Agent: postfix

Hope this helps!