Rsync error when connecting to CentOS: rsync error: error in rsync protocol data stream (code 12) at io.c(600) [sender=3.0.6]

  We helped rebuild a backup VM which receives data over rsync today; the first rsync attempt failed with the vague error message:  
rsync error: error in rsync protocol data stream (code 12) at io.c(600) [sender=3.0.6]
  The problem ended up being that the rsync package was not installed. A simple:  
yum install rsync -y
  …fixed the problem and shortly the backups were back to normal.