At Sun, 31 Jan 2021 09:27:10 +1100 (EST), Dave Horsfall wrote: Subject: Re: [TUHS] reboot(2) system call > > On Tue, 26 Jan 2021, Greg A. Woods wrote: > > > The lore I was told at the time was that you alwasy ran three and > > that it didn't matter if they were all on the same line with > > semicolons or not because of the very fact that the second one would > > block. > > What I was taught was: > > % sync > % sync > % sync > > and never: > > % sync; sync; sync > > The theory was that by waiting for the shell prompt each time, it gave > the buffer pool enough time to be flushed. If waiting was the true reason, then any sane person would have put a sleep in there instead so as to avoid any variance in typing (and terminal) speed. On at least a large number of old systems I've used either the first or the second invocation did block and not return if there were still any dirty blocks it made the sync() call. It was trivial to see that the system was busy writing while one waited for the shell prompt to re-appear if one could see the disk activity lights (or hear them) from the console, as was usually easy to do on desktop systems. Since many of those old systems I used were Xenix of one flavour or another, perhaps it was only those that waited for sync I/O to complete. -- Greg A. Woods Kelowna, BC +1 250 762-7675 RoboHack Planix, Inc. Avoncote Farms