PASSWD
Section: User utilities (1)Updated: Jan 26 2012
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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
-
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.
- -e
-
This is a quick way to expire a password for an account. The user will be
forced to change the password during the next login attempt.
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
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 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.
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>
Index
- NAME
- SYNOPSIS
- DESCRIPTION
- OPTIONS
- Remember the following two principles
- EXIT CODE
- CONFORMING TO
- FILES
- BUGS
- SEE ALSO
- AUTHOR
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Time: 05:29:07 GMT, December 24, 2015