On Thu, Dec 22, 2005 at 11:47:13AM -0500, Tom Lane wrote: > Martijn van Oosterhout <kleptog@xxxxxxxxx> 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@xxxxxxxxxxxxx Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
