PASSWD(1)							   User Commands							 PASSWD(1)

NAME

       passwd - change user password

SYNOPSIS

       passwd [options] [LOGIN]

DESCRIPTION

       The passwd command changes passwords for user accounts. A normal user may only change the password for his/her own account, while the
       superuser may change the password for any account.  passwd also changes the account or associated password validity period.

   Password Changes
       The user is first prompted for his/her old password, if one is present. This password is then encrypted and compared against the stored
       password. The user has only one chance to enter the correct password. The superuser is permitted to bypass this step so that forgotten
       passwords may be changed.

       After the password has been entered, password aging information is checked to see if the user is permitted to change the password at this
       time. If not, passwd refuses to change the password and exits.

       The user is then prompted twice for a replacement password. The second entry is compared against the first and both are required to match
       in order for the password to be changed.

       Then, the password is tested for complexity. As a general guideline, passwords should consist of 6 to 8 characters including one or more
       characters from each of the following sets:

       o   lower case alphabetics

       o   digits 0 thru 9

       o   punctuation marks

       Care must be taken not to include the system default erase or kill characters.  passwd will reject any password which is not suitably
       complex.

   Hints for user passwords
       The security of a password depends upon the strength of the encryption algorithm and the size of the key space. The legacy UNIX System
       encryption method is based on the NBS DES algorithm. More recent methods are now recommended (see ENCRYPT_METHOD). The size of the key
       space depends upon the randomness of the password which is selected.

       Compromises in password security normally result from careless password selection or handling. For this reason, you should not select a
       password which appears in a dictionary or which must be written down. The password should also not be a proper name, your license number,
       birth date, or street address. Any of these may be used as guesses to violate system security.

       You can find advices on how to choose a strong password on http://en.wikipedia.org/wiki/Password_strength

OPTIONS

       The options which apply to the passwd command are:

       -a, --all
	   This option can be used only with -S and causes show status for all users.

       -d, --delete
	   Delete a user's password (make it empty). This is a quick way to disable a password for an account. It will set the named account
	   passwordless.

       -e, --expire
	   Immediately expire an account's password. This in effect can force a user to change his/her password at the user's next login.

       -h, --help
	   Display help message and exit.

       -i, --inactive INACTIVE
	   This option is used to disable an account after the password has been expired for a number of days. After a user account has had an
	   expired password for INACTIVE days, the user may no longer sign on to the account.

       -k, --keep-tokens
	   Indicate password change should be performed only for expired authentication tokens (passwords). The user wishes to keep their
	   non-expired tokens as before.

       -l, --lock
	   Lock the password of the named account. This option disables a password by changing it to a value which matches no possible encrypted
	   value (it adds a '!' at the beginning of the password).

	   Note that this does not disable the account. The user may still be able to login using another authentication token (e.g. an SSH key).
	   To disable the account, administrators should use usermod --expiredate 1 (this set the account's expire date to Jan 2, 1970).

	   Users with a locked password are not allowed to change their password.

       -n, --mindays MIN_DAYS
	   Set the minimum number of days between password changes to MIN_DAYS. A value of zero for this field indicates that the user may change
	   his/her password at any time.

       -q, --quiet
	   Quiet mode.

       -r, --repository REPOSITORY
	   change password in REPOSITORY repository

       -S, --status
	   Display account status information. The status information consists of 7 fields. The first field is the user's login name. The second
	   field indicates if the user account has a locked password (L), has no password (NP), or has a usable password (P). The third field
	   gives the date of the last password change. The next four fields are the minimum age, maximum age, warning period, and inactivity
	   period for the password. These ages are expressed in days.

       -u, --unlock
	   Unlock the password of the named account. This option re-enables a password by changing the password back to its previous value (to the
	   value before using the -l option).

       -w, --warndays WARN_DAYS
	   Set the number of days of warning before a password change is required. The WARN_DAYS option is the number of days prior to the
	   password expiring that a user will be warned that his/her password is about to expire.

       -x, --maxdays MAX_DAYS
	   Set the maximum number of days a password remains valid. After MAX_DAYS, the password is required to be changed.

CAVEATS

       Password complexity checking may vary from site to site. The user is urged to select a password as complex as he or she feels comfortable
       with.

       Users may not be able to change their password on a system if NIS is enabled and they are not logged into the NIS server.

       passwd uses PAM to authenticate users and to change their passwords.

FILES

       /etc/passwd
	   User account information.

       /etc/shadow
	   Secure user account information.

       /etc/pam.d/passwd
	   PAM configuration for passwd.

EXIT VALUES

       The passwd command exits with the following values:

       0
	   success

       1
	   permission denied

       2
	   invalid combination of options

       3
	   unexpected failure, nothing done

       4
	   unexpected failure, passwd file missing

       5
	   passwd file busy, try again

       6
	   invalid argument to option

SEE ALSO

       passwd(5), shadow(5), usermod(8).

User Commands							    06/24/2011								 PASSWD(1)