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:

   *   lower case alphabetics

   *   digits 0 thru 9

   *   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

   -R, --root CHROOT_DIR
       Apply changes in the CHROOT_DIR directory and use the configuration
       files from the CHROOT_DIR directory.

   -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

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

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