1. Enable logging of debug messages in SYSLOG:
# cp /etc/syslog.conf /etc/syslog.conf.prev
# vi /etc/syslog.conf

Add the following line:

  1. Then restart syslogd:
# touch /var/log/debug.log
# /sbin/init.d/syslogd stop && /sbin/init.d/syslogd start
  1. You can enable debugging for all modules like so:
# touch /etc/pam_debug

OR you can enable debugging only for the modules you’re interested in by adding debug to the end of the relevant lines in /etc/pam.conf or the other /etc/pam.d/* files:

login   auth    required    pam_unix.so debug
  1. Then debugging messages should start appearing in /var/log/debug.log