If you’re a Unix admin, it helps to know how password aging is managed and how you can determine when a password was last changed or force a change in the near future. The key to understanding how password aging information is stored on Unix systems is knowing how and where information about dates related to user passwords is maintained.

Regular users (anyone without root access) cannot look at the contents of the /etc/shadow file where password aging parameters are stored. The contents of this file were separated from the /etc/passwd file a lot of years ago (back in the mid-eighties) to keep user password hashes away from the prying eyes of anyone but root. Even so, users can pull up information about their password settings using the chage command.

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