password   required   pam_unix.so nullok obscure min=4 max=8 md5

    #
    # /etc/pam.d/common-password - password-related modules common to all services
    #
    # This file is included from other service-specific PAM config files,
    # and should contain a list of modules that define the services to be
    # used to change user passwords. The default is pam_unix.
     
    # Explanation of pam_unix options:
    #
    # The "sha512" option enables salted SHA512 passwords. Without this option,
    # the default is Unix crypt. Prior releases used the option "md5".
    #
    # The "obscure" option replaces the old `OBSCURE_CHECKS_ENAB' option in
    # login.defs.
    #
    # See the pam_unix manpage for other options.
     
    # As of pam 1.0.1-6, this file is managed by pam-auth-update by default.
    # To take advantage of this, it is recommended that you configure any
    # local modules either before or after the default block, and use
    # pam-auth-update to manage selection of other modules. See
    # pam-auth-update(8) for details.
     
    # here are the per-package modules (the "Primary" block)
    password [success=1 default=ignore] pam_unix.so obscure sha512
    # here's the fallback if no module succeeds
    password requisite pam_deny.so
    # prime the stack with a positive return value if there isn't one already;
    # this avoids us returning an error just because nothing sets a success code
    # since the modules above will each just jump around
    password required pam_permit.so
    # and here are more per-package modules (the "Additional" block)
    # end of pam-auth-update config