On Thu, Dec 22, 2005 at 11:47:13AM -0500, Tom Lane wrote:
> Martijn van Oosterhout <kleptog@svana.org> writes:
> > On Wed, Dec 21, 2005 at 11:30:15PM -0800, Benjamin Arai wrote:
> >> Somebody said running "sync ; sync; sync" from the console. This seems
>
> > The reason is partly historical. On some OSes running sync only starts
> > the process but returns immediatly. However, there can only be one sync
> > at a time so the second sync waits for the first the finish. The third
> > is just for show. However, on Linux at least the one sync is enough.
>
> No, the second and third are both a waste of time. sync tells the
> kernel to flush any dirty buffers to disk, but doesn't wait for it to
> happen.
>
> There is a story that the advice to type sync twice was originally given
> to operators of an early Unix system, as a quick-and-dirty way of making
> sure that they didn't power the machine down before the sync completed.
> I don't know if it's true or not, but certainly the value would only
> appear if you type sync<RETURN>sync<RETURN> so that the first sync is
> actually issued before you type the next one. Typing them all on one
> line as depicted is just a waste of finger motion.
How would sync<RETURN>sync<RETURN> differ from sync;sync? The second
case will wait for the first command to return, or is there a race
condition that's reduced by typing by hand?
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461