UNIX passwd structure
passwd syntax:
username:password:uid:gid:comment:home-directory:login-shell
username: Contains the user or login name.
password: Contains an x, a placeholder for the encrypted password. The encrypted password is stored in the shadow file.
uid: Contains a user identification (UID) number that identifies the user to the system.
gid: Contains a group identification (GID) number that identifies the user’s primary group.
comment: Usually contains the full name of the user. (This field is informational only.)
home-directory: Contains the user’s home directory path name.
login-shell: Contains the user’s default login shell, such as /bin/bash
shadow syntax:
username:password:lastchg:min:max:warn:inactive:expire
username: Contains the user or login name.
password: The encrypted user password
lastchg: Indicates the number of days between January 1, 1970, and the last password modification date.
min: Contains the minimum number of days required between password changes.
max: Contains the maximum number of days the password is valid before the user is prompted to specify a new password.
inactive: Contains the number of days a user account can be inactive before being locked.
expire: Contains the absolute date when the user account expires. Past this date, the user cannot log in to the system.
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