usermod > is for modifying the named user account.
-G > option tells it to modify the secondary groups that that user belongs to (-g does the primary group)
In a terminal do,
man usermod this will open the
manual page for usermod. Try it with some other command. It will work so long as you installed the man packages.
/etc/rc.d/rc.messagebus reload > rc.messagebus is the script that starts and stops the messagebus service, the reload option tells it to reload its config info to take notice of the modified group settings. Another way to reload them would be to restart the computer, but why do that when you don't really have to
Also the problem you have encounter is explained more in depth in this thread,
http://www.linuxquestions.org/questi...d-this-566862/