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:
It must be a valid account name, which exist on the system.
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).
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.
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 are no minimum
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
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
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.
This field is reserved for future use.
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.
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 ⟨http://pkg-shadow.alioth.debian.org/⟩. If
you have a bug report for this manual page, see
⟨http://pkg-shadow.alioth.debian.org/getinvolved.php⟩. This page was
obtained from the project's upstream Git repository
⟨git://anonscm.debian.org/git/pkg-shadow/shadow.git⟩ on 2017-03-13.
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 firstname.lastname@example.org
shadow-utils 4.4 02/18/2017 SHADOW(5)