passwd - phpMan

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 warndays] [-i inac-
tivedays] [-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 initial-
izes 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 function cor-
rectly.

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 pass-
word 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 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 (includ-
ing 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 unre-
lated to any previous password. Use long passwords (say 8 characters long).
You might use a word pair with punctuation inserted, a passphrase (an under-
standable 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. Vigi-
lence 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 Filesystem 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.