NAME
passwd - update user's authentication tokens
SYNOPSIS
passwd [-k] [-l] [-u [-f]] [-d] [-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 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
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 delete 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
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 security 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 password, 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.
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).
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 <gafton@redhat.com>