shadow(5) — Linux manual page


SHADOW(5)            File Formats and Configuration            SHADOW(5)

NAME         top

       shadow - shadowed password file

DESCRIPTION         top

       shadow 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

           Refer to crypt(3) for details on how this string is

           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

           An empty field means that password aging features are

       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,

       reserved field
           This field is reserved for future use.

FILES         top

           User account information.

           Secure user account information.

           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 ALSO         top

       chage(1), login(1), passwd(1), passwd(5), pwck(8), pwconv(8),
       pwunconv(8), su(1), sulogin(8).

COLOPHON         top

       This page is part of the shadow-utils (utilities for managing
       accounts and shadow password files) project.  Information about
       the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, send it to  This page was obtained
       from the project's upstream Git repository
       ⟨⟩ on 2024-06-15.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

shadow-utils 4.14.0            06/15/2024                      SHADOW(5)

Pages that refer to this page: chage(1)expiry(1)lslogins(1)passwd(1)systemd-firstboot(1)getspnam(3)getspnam(3@@shadow-utils)shadow(3)login.defs(5)passwd(5)passwd(5@@shadow-utils)credentials(7)grpck(8)pam_unix(8)pwck(8)useradd(8)usermod(8)vipw(8)