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PASSWD(1) User utilities PASSWD(1)

NAME
passwd - update a user's authentication tokens(s)

SYNOPSIS
passwd [-k] [-l] [-u [-f]] [-d] [-n mindays] [-x maxdays] [-w warndays] [-i inactivedays]
[-S] [--stdin] [username]

DESCRIPTION
Passwd is used to update a user's authentication token(s).

Passwd is configured to work through the Linux-PAM API. Essentially, it initializes
itself as a "passwd" service with Linux-PAM and utilizes configured password modules to
authenticate and then update a user's password.

A simple entry in the Linux-PAM configuration file for this service would be:

#
# passwd service entry that does strength checking of
# a proposed password before updating it.
#
passwd password requisite \
/usr/lib/security/pam_cracklib.so retry=3
passwd password required \
/usr/lib/security/pam_unix.so use_authtok
#

Note, other module-types are not required for this application to function correctly.

OPTIONS
-k The option, -k, is used to indicate that the update should only be for expired
authentication tokens (passwords); the user wishes to keep their non-expired tokens
as before.

-l This option is used to lock the specified account and it is available to root only.
The locking is performed by rendering the encrypted password into an invalid string
(by prefixing the encrypted string with an !).

--stdin
This option is used to indicate that passwd should read the new password from stan-
dard input, which can be a pipe.

-u This is the reverse of the -l option - it will unlock the account password by
removing the ! prefix. This option is available to root only. By default passwd
will refuse to create a passwordless account (it will not unlock an account that
has only "!" as a password). The force option -f will override this protection.

-d This is a quick way to disable a password for an account. It will set the named
account passwordless. Available to root only.

-n This will set the minimum password lifetime, in days, if the user's account sup-
ports password lifetimes. Available to root only.

-x This will set the maximum password lifetime, in days, if the user's account sup-
ports password lifetimes. Available to root only.

-w This will set the number of days in advance the user will begin receiving warnings
that her password will expire, if the user's account supports password lifetimes.
Available to root only.

-i This will set the number of days which will pass before an expired password for
this account will be taken to mean that the account is inactive and should be dis-
abled, if the user's account supports password lifetimes. Available to root only.

-S This will output a short information about the status of the password for a given
account. Available to root user only.

Remember the following two principles
Protect your password.
Don't write down your password - memorize it. In particular, don't write it down
and leave it anywhere, and don't place it in an unencrypted file! Use unrelated
passwords for systems controlled by different organizations. Don't give or share
your password, in particular to someone claiming to be from computer support or a
vendor. Don't let anyone watch you enter your password. Don't enter your password
to a computer you don't trust or if things Use the password for a limited time and
change it periodically.

Choose a hard-to-guess password.
passwd will try to prevent you from choosing a really bad password, but it isn't
foolproof; create your password wisely. Don't use something you'd find in a dic-
tionary (in any language or jargon). Don't use a name (including that of a spouse,
parent, child, pet, fantasy character, famous person, and location) or any varia-
tion of your personal or account name. Don't use accessible information about you
(such as your phone number, license plate, or social security number) or your envi-
ronment. Don't use a birthday or a simple pattern (such as backwards, followed by
a digit, or preceded by a digit. Instead, use a mixture of upper and lower case
letters, as well as digits or punctuation. When choosing a new password, make sure
it's unrelated to any previous password. Use long passwords (say 8 characters
long). You might use a word pair with punctuation inserted, a passphrase (an
understandable sequence of words), or the first letter of each word in a
passphrase.

These principles are partially enforced by the system, but only partly so. Vigilence on
your part will make the system much more secure.

EXIT CODE
On successful completion of its task, passwd will complete with exit code 0. An exit code
of 1 indicates an error occurred. Textual errors are written to the standard error
stream.

CONFORMING TO
Linux-PAM (Pluggable Authentication modules for Linux).
Note, if your distribution of Linux-PAM conforms to the Linux Filesystem Standard, you may
find the modules in /lib/security/ instead of /usr/lib/security/, as indicated in the
example.

FILES
/etc/pam.d/passwd - the Linux-PAM configuration file

BUGS
None known.