shadow(5) — Linux manual page


SHADOW(5)               File Formats and Conversions               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 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.

           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

       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

           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

           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

           After expiration of the password and this expiration period is
           elapsed, no login is possible using the current user's password.
           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.

           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         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 2020-09-18.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-08-28.)  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 4.8.1               09/18/2020                        SHADOW(5)

Pages that refer to this page: chage(1)expiry(1)lslogins(1)passwd(1)systemd-firstboot(1)systemd-firstboot.service(1)endspent(3)fgetspent(3)fgetspent_r(3)getspent(3)getspent_r(3)getspnam(3)getspnam(3@@shadow-utils)getspnam_r(3)lckpwdf(3)putspent(3)setspent(3)sgetspent(3)sgetspent_r(3)shadow(3)ulckpwdf(3)login.defs(5)passwd(5)passwd(5@@shadow-utils)credentials(7)grpck(8)pam_unix(8)pwck(8)vigr(8)vigr(8@@util-linux)vipw(8)