As with the passwd file, each field in the shadow file is also separated with ":" colon characters, and are as follows:
Username, up to 8 characters. Case-sensitive, usually all lowercase. A direct match to the username in the /etc/passwd file.
Password, 13 character encrypted. A blank entry (eg. ::) indicates a password is not required to log in (usually a bad idea), and a ``*'' entry (eg. :*:) indicates the account has been disabled.
The number of days (since January 1, 1970) since the password was last changed.
The number of days before password may be changed (0 indicates it may be changed at any time)
The number of days after which password must be changed (99999 indicates user can keep his or her password unchanged for many, many years)
The number of days to warn user of an expiring password (7 for a full week)
The number of days after password expires that account is disabled
The number of days since January 1, 1970 that an account has been disabled
A reserved field for possible future use