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
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 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 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
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
For more complete information on how to configure this application
with
Linux-PAM,
see the
Linux-PAM System Administrators' Guide at
/usr/share/doc/pam...
