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

 passwd [-k] [-l] [-u [-f]] [-d] [-S] [username]
 

 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_pwdb.so use_authtok
 #
 
 Note, other module-types are not required for this appli­
 cation to function correctly.
 

 -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 standard input, which
 unlock the account password by removing the ! pre­
 fix. 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 password­
 less. Available to root only.
 
 -S This will output a short information about the sta­
 tus of the password for a given account. Available
 to root user only.
 

 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 any­
 one 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 dictionary (in any language or jargon).
 Don't use a name (including that of a spouse, par­
 ent, 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 security number) or your environ­
 ment. Don't use a birthday or a simple pattern
 (such as backwards, followed by a digit, or pre­
 ceded by a digit. Instead, use a mixture of upper
 and lower case letters, as well as digits or punc­
 tuation. 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
 
 These principles are partially enforced by the system, but
 only partly so. Vigilence on your part will make the sys­
 tem much more secure.
 

 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.
 

 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.
 

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

 None known.
 

 pam(8), and pam_chauthok(2).
 
 For more complete information on how to configure this
 application with Linux-PAM, see the Linux-PAM System
 Administrators' Guide at
 <http://parc.power.net/morgan/Linux-PAM/index.html>
 

 Cristian Gafton <gafton@redhat.com>