SHADOW - Online Linux Manual PageSection : 5
Updated : 03/06/2023
Source : shadow−utils 4​.13
Note : File Formats and Configuration

NAMEshadow − shadowed password file

DESCRIPTIONshadow is a file which contains the password information for the system's accounts and optional aging information​. This file must not be readable by regular users if password security is to be maintained​. Each line of this file contains 9 fields, separated by colons (:), in the following order: login name It must be a valid account name, which exist on the system​. encrypted password This field may be empty, in which case no passwords are required to authenticate as the specified login name​. However, some applications which read the /etc/shadow file may decide not to permit any access at all if the password field is empty​. A password field which starts with an exclamation mark means that the password is locked​. The remaining characters on the line represent the password field before the password was locked​. Refer to crypt(3) for details on how this string is interpreted​. If the password field contains some string that is not a valid result of crypt(3), for instance ! or *, the user will not be able to use a unix password to log in (but the user may log in the system by other means)​. date of last password change The date of the last password change, expressed as the number of days since Jan 1, 1970 00:00 UTC​. The value 0 has a special meaning, which is that the user should change her password the next time she will log in the system​. An empty field means that password aging features are disabled​. minimum password age The minimum password age is the number of days the user will have to wait before she will be allowed to change her password again​. An empty field and value 0 mean that there is no minimum password age​. maximum password age The maximum password age is the number of days after which the user will have to change her password​. After this number of days is elapsed, the password may still be valid​. The user should be asked to change her password the next time she will log in​. An empty field means that there are no maximum password age, no password warning period, and no password inactivity period (see below)​. If the maximum password age is lower than the minimum password age, the user cannot change her password​. password warning period The number of days before a password is going to expire (see the maximum password age above) during which the user should be warned​. An empty field and value 0 mean that there are no password warning period​. password inactivity period The number of days after a password has expired (see the maximum password age above) during which the password should still be accepted (and the user should update her password during the next login)​. After expiration of the password and this expiration period is elapsed, no login is possible for the user​. The user should contact her administrator​. An empty field means that there are no enforcement of an inactivity period​. account expiration date The date of expiration of the account, expressed as the number of days since Jan 1, 1970 00:00 UTC​. Note that an account expiration differs from a password expiration​. In case of an account expiration, the user shall not be allowed to login​. In case of a password expiration, the user is not allowed to login using her password​. An empty field means that the account will never expire​. The value 0 should not be used as it is interpreted as either an account with no expiration, or as an expiration on Jan 1, 1970​. reserved field This field is reserved for future use​.

FILES/etc/passwd User account information​. /etc/shadow Secure user account information​. /etc/shadow− Backup file for /etc/shadow​. Note that this file is used by the tools of the shadow toolsuite, but not by all user and password management tools​.

SEE ALSOchage(1), login(1), passwd(1), passwd(5), pwck(8), pwconv(8), pwunconv(8), su(1), sulogin(8)​.
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