Is there any way to allow users to access the etc/passwd file for commands like whoami but not be able to read the file? If I don't put a user in the security group and change the permissions on the etc/passwd file to 640 (rw-r-----) the users can login but the whoami command doesn't work for them. If I give other the read permission whoami works but the user can also read the file. I want user to be able to run the whoami command but not see what is in the /etc/passwd file.

If you have "sudo", add that for the users. Or make it setuid.

I would suggest setting up sudo for whoami. If you want to make it completely transparent set up sudo, so the user doesn't need to type in a password and then create an alias that does 'sudo whoami'.

You can't make /etc/passwd unreadable, because commands like "ls" rely on it to associate numeric uids to usernames.

If you make /etc/passwd unreadable to a user, then whenever that user types "ls -l", or certain other commands, they will just see numbers instead of usernames as the file owners.