File common-password.pamd of Package pam

#
# /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 "nullok" option allows users to change an empty password, else
# empty passwords are treated as locked accounts.
#
password        requisite       pam_cracklib.so
password        required        pam_unix.so     use_authtok nullok try_first_pass