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

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       shadow - <?><?><?><?><?><?><?><?><?>

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       shadow is a file which contains the password information for the
       system's accounts and optional aging information.

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       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 exists on the system.

       encrypted password
           If the password field is empty, the user can log in without a
           password. However, some applications that read the /etc/shadow file
           might block access if the password field is empty.

           If the password field begins with an exclamation mark !, 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 a string that is not a valid result
           of crypt(3), for instance ! or *, the user cannot use a UNIX
           password to log in. However, 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 1970-01-01 00:00:00 UTC.

           The value 0 indicates that the user must change their password the
           next time they log in to the system.

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       minimum password age
           The minimum password age is the number of days the user must wait
           before they can change their 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
           must change their password.

           After this number of days has elapsed, the password may still be
           valid. The user is prompted to change their password at the next
           login.

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       password warning period
           The number of days before a password expires (see the maximum
           password age above) during which the user is warned.

           An empty field and value 0 mean that there is no password warning
           period.

       password inactivity period
           The number of days after a password expires (see the maximum
           password age above) during which the password is still accepted,
           and the user must update their password at the next login.

           After the password expires and the password inactivity period
           elapses, the user cannot log in and must contact their
           administrator.

           An empty string means that no inactivity period is enforced.

       account expiration date
           The date when the account expires, expressed as the number of days
           since 1970-01-01.

           Note that account expiration differs from password expiration.
           Account expiration prevents the user from logging in, whereas
           password expiration only prevents users from logging in with their
           password.

           An empty field means that the account never expires.

           The value 0 should not be used, as it is interpreted either as an
           account with no expiration or as an expiration date of 1970-01-01.

       reserved field
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       /etc/passwd
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       /etc/shadow
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       /etc/shadow-
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           <?><?><?><?><?><?><?> shadow
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       chage(1), login(1), passwd(1), passwd(5), pwck(8), pwconv(8),
       pwunconv(8), su(1), sulogin(8).

shadow-utils 4.18.0               2025-06-27                         SHADOW(5)