Tracking the polling software

[Tony Pursell]

On Mon, 2010-12-13 at 13:05 +0100, Nils Kassube wrote:
> Tony Pursell wrote:
> > On Mon, 2010-12-13 at 06:36 +0100, Nils Kassube wrote:
> > > There should be nothing to sync every ~2 seconds on an idle system.
> > > On my system only the CD/DVD drive is polled in regular
> > > intervalls.
> > 
> > The system doesn't know if there is anything to sync without looking
> > first, so it just does it - at least that is what happened in my old
> > Unix days (1983 to 2000 approx).
> 
> Hmm, that's interesting. As I understand it, the system should know if 
> there is anything to sync (i.e. open files with data not yet written to 
> the disk). Everything to look at should be in memory and there should be 
> no disk access if the system is idle.
> 
> 
> Nils
> 

Syncing is much lower level than that. Apps, like OpenOffice.org have
there own recovery arrangements at the higher level. What syncing is, is
something much lower level in the file systems and buffering of writes
(see man 8 sync). 

Back in the Unix days the rule was to run sync three times, run haltsys
then press the off button.  Pressing the off button without syncing
always forced fsck on re-start.  Whether it found a problem or not
depended on whether there was any write activity at the time of switch
off since the last auto sync. 

Unfortunately, I only have a vague technical understanding of what is
going on here, so I will bow out of any further discussion, but I do
thing that syncing is the reason behind regular disk activity.

Tony