[TUHS] shutdown for pre-v7 unix

[Dan Stromberg]

On Wed, Jul 16, 2014 at 2:12 PM, Dave Horsfall <dave at horsfall.org> wrote:
> On Wed, 16 Jul 2014, Mark Longridge wrote:
>
>> I've been typing sync;sync at the shell prompt then hitting ctrl-e to
>> get out of simh to shutdown v5 and v6 unix.
>
> The "correct" way used to be:
>
>     sync
>     sync
>     sync

3 sync's was net.wisdom for a long time, but some discussions in the
Linux mailing lists suggested that 2 was enough all along.

The first schedules all dirty buffers to be flushed to disk.

The second does the same, but to provide an ordering guarantee,
doesn't return until the dirty buffers from the first are finished.

Hence the 2.

But I'm a relative newcomer to *ix - I didn't get involved until SunOS 4.