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] [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 func-
    tion 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 standard 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 avail-
    able 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 supports password lifetimes. Available to root
    only.

    -x   This will set the maximum password lifetime, in days, if the
    user's account supports 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 disabled, 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 con-
    trolled 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  pass-
    word, 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 environment.
    Don't use a birthday or a simple pattern  (such as backwards,
    followed by a digit, or preceded by a digit. Instead, use a mix-
    ture 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 (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 Filesys-
    tem 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.

SEE ALSO
    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>

AUTHOR
    Cristian Gafton <gafton@redhat.com>