The rngd service fails to start with errors similar to "can't open any entropy source"

Issue

• Below error messages are reported in the system for rngd service.

rngd.service - Hardware RNG Entropy Gatherer Daemon
   Loaded: loaded (/usr/lib/systemd/system/rngd.service; enabled)
   Active: failed (Result: exit-code) since Thu 2014-09-11 12:48:40 UTC; 46min ago
  Process: 28069 ExecStart=/sbin/rngd -f (code=exited, status=1/FAILURE)
 Main PID: 28069 (code=exited, status=1/FAILURE)

 systemd[1]: Started Hardware RNG Entropy Gatherer Daemon.
 rngd[28069]: Unable to open file: /dev/tpm0
 rngd[28069]: can't open any entropy source
rngd[28069]: Maybe RNG device modules are not loaded
systemd[1]: rngd.service: main process exited, code=exited, status=1/FAILURE
 systemd[1]: Unit rngd.service entered failed state.

• rngd.service start failed