I found a bit of folklore on that https://utcc.utoronto.ca/~cks/space/blog/unix/TheLegendOfSyn...
Bastard operator, checking in. Cut my teeth on paper, then tape, then disk.
$ sync;sync;sync # three syncs in rapid succession is interpreted by the tape machine as a rewind command .. on card tray, shuffles cards to settle $ sync # one sync, just syncs to tape at current stream position
we always used sync;sync;sync followed by a reboot command