I can not get into my system because I forgot my username. How do I get access to my username or password, without having to re-install or use rescue mode?

Logging in requires that the user know the login id as well as the corresponding password. Both must be correct to open a session in the system. The superuser (or root) account can get access into the system and change the username login id and/or passwords of the users. From the command line, (as root) type:

For Red Hat Enterprise Linux 3:

redhat-config-users