Usernames greater than 8 characters in length fail on AIX. You may receive the message "msg 3004-300 You entered an invalid login name or password".
By default AIX does not support usernames longer than 8 characters.
To determine if this is the issue run the following command:-
# lsattr -El sys0 -a max_logname
This will report the current maximum login name length set at boot time, e.g. "max_logname 9 Maximum login name length at boot time True"
To increase the OS limit in AIX you can run the following command:-
# chdev -l sys0 -a max_logname=21
You will then need to reboot this host when appropriate for these changes to take effect
Use a "user-override" file to override the usernames to less than 8 characters. The below example, would allow the firstname.lastname@example.org user to log on with the username shortnam instead.
# more /etc/opt/quest/vas/user-override
If you use CDE to access the system this will now allow you to enter more than 8 characters in to the login name unless you set the max_logname to a greater value.
If you use SSH to access these hosts you may only receive an access denied message, if you run a separate SSHD with debug enabled you will see a message similar to the following if the username length is an issue:
debug3: AIX/loginrestrictions returned -1 msg 3004-300 You entered an invalid login name or password
You will see the following message if the system is not suffering from this issue:
debug3: AIX/loginrestrictions returned 0 msg (none)
Not sure if this is related, but the user was also seeing the message "Login restricted for NOUSER" whenever trying to log in using the username that was over the limit.