The shadow file

The /etc/shadow file is an access-restricted ASCII system file that stores the user's encrypted passwords and associated information.  The  shadow  file  can  be  used  in  conjunction  with  other  shadow  sources, including the NIS maps, passwd uid, passwd by nam, and the NIS+ table passwd . The fields for each user are separated by colons. Each user    is    divided   from    the next through a new line. Unlike the /etc/passwd file, /etc/shadow does not have general read permission.

Every entry in the shadow file has the form:

username:password:lastchg:min:max:warn:inactive:expire:

flag

The fields are described as follows:

username

username specifies the user's login name (UID).

password

This specifies a 34-character encrypted password for the user, a lock string to denote in which the login is not accessible, or no string, that shows in which there is no password for the login.

lastchg

The number of days among January 1,  1970,  and the date in which the password was last modified through the user.

min

This denotes the minimum number of days within which a user can change password.

max

This denotes the maximum number of days during that the password remains valid.

warn

The number of days before the password   expires   which the user is warned. Which Indicates the expiry of password.

inactive

This denotes the number of days of inactivity permit for the user.

expire

This denotes an absolute date specifying when the login might no longer be used.

flag

This denotes in which it is reserved for future use, and set to zero. Presently it is not used. Associated files get updated when the passwd command is used

/etc/pam.d/passwd

/etc/shadow - shadow password file

Note: In case of SUN and SCO. /etc/passwd. An encrypted password consists of 34 characters which   are   selected   from   a 64-character alphabet    (.,   /,   0-9,   A-Z,   a-z).   In   sequence   to   make   the   system administration     manageable,    /etc/shadow      entries   should   appear   accurately  in  the  similar  order   as /etc/passwd entries;  this involves "+" and "-" entries if the compute source is being used.