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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 warn-
days] [-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 uti-
lizes 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 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 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
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 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 loca-
tion) or any variation of your personal or account name. Don't
use accessible information about you (such as your phone num-
ber, license plate, or social security number) or your environ-
ment. Don't use a birthday or a simple pattern (such as back-
wards, followed by a digit, or preceded by a digit. Instead,
use a mixture of upper and lower case letters, as well as dig-
its 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 punc-
tuation 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
AUTHOR
Cristian Gafton
Red Hat Linux Aug 23 2004 PASSWD(1)
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