When you try to login to a user using su, you get "su: Authentication failure" message

su - myuser


su: Authentication failure


  1. Check if the password is expired -> # chage -l myuser
  2. Check the pam error: # more /etc/pam.d/login
  3. Check any error: # pam_tally2 --user=myuser
  4. If not "0" on the above, just reset: # pam_tally2 --user=pe1adm --reset

This will solve your problem.