PASSWD(1) User utilities PASSWD(1)
NAME
passwd - update user's authentication tokens
SYNOPSIS
passwd [-k] [-l] [-u [-f]] [-d] [-e] [-n mindays] [-x maxdays] [-w warndays] [-i inactivedays] [-S] [--stdin]
[username]
DESCRIPTION
The passwd utility is used to update user's authentication token(s).
This task is achieved through calls to the Linux-PAM and Libuser 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 global 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 pam_cracklib.so retry=3
passwd password required pam_unix.so use_authtok
#
Note, other module types are not required for this application to function correctly.
OPTIONS
-k, --keep
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, --lock
This option is used to lock the password of 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 !). Note that the account is not fully locked - the user can still log in by
other means of authentication such as the ssh public key authentication. Use chage -E 0 user command
instead for full account locking.
--stdin
This option is used to indicate that passwd should read the new password from standard input, which can
be a pipe.
-u, --unlock
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.
-f, --force
Force the specified operation.
-n, --minimum DAYS
This will set the minimum password lifetime, in days, if the user's account supports password life‐
times. Available to root only.
-x, --maximum DAYS
This will set the maximum password lifetime, in days, if the user's account supports password life‐
times. Available to root only.
-w, --warning DAYS
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, --inactive DAYS
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 disabled, if the user's account supports pass‐
word lifetimes. Available to root only.
-S, --status
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 any‐
where, 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 "look funny"; someone may be trying to hijack your
password. Use the password for a limited time and change it periodically.
Choose a hard-to-guess password.
passwd through the calls to the pam_cracklib PAM module 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
dictionary (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 variation of your personal or account name.
Don't use accessible information about you (such as your phone number, license plate, or social secu‐
rity number) or your environment. Don't use a birthday or a simple pattern (such as "qwerty", "abc",
or "aaa"). Don't use any of those 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 pass‐
word, make sure it's unrelated to any previous password. Use long passwords (say at least 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.
FILES
/etc/pam.d/passwd - the Linux-PAM configuration file
BUGS
None known.
SEE ALSO
pam(8), pam.d(5), libuser.conf(5), and pam_chauthtok(3).
For more complete information on how to configure this application with Linux-PAM, see the Linux-PAM System
Administrators' Guide.
AUTHOR
Cristian Gafton <[email protected]>
GNU/Linux Jun 20 2012 PASSWD(1)
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