Password field of shadow file
 

What's the difference between * and ! in the password field of the shadow file?

According to the man 5 shadow page there is no functional difference.

I think it is just that those characters can not be in a legitimate password hash, and as such means that no password could ever ever match it.

Ok, so there's not really a difference unless the ! is followed by a password hash. Then it means the account was locked and can be unlocked to use the same password. I still have ! (or !! on CentOS and Fedora) for accounts that never could be logged in, and weren't locked by an administrator. Thanks for the info.