Back in the day (old Unix), the sync call would return right away, and the kernel would sync in the background. Unless there was a current background sync happ

Back in the day (old Unix), the sync call would return right away, and the kernel would sync in the background. Unless there was a current background sync happening -- then sync would block until the first one finished, which is why you would have two sync's in a row. The third sync was thrown in just for luck.