Kill the power faster than poweroff?

Donald Becker becker at
Thu Sep 11 15:27:11 EDT 2003

On Thu, 11 Sep 2003 alan at wrote:
>     I've read in other places that you need to repeat the sync command a
>     number of times (I seem to remember the article saying 3 times in
>     particular, though I can't remember how they arrived at that number) in
>     order to guarantee writing.  Even then it seems like there ought to be
>     race-condition like issues.

I was told over two decades ago.  The principle was that the first sync
queued the pages to write, and the second sync didn't start until the
first write list had finished.  The third was just to make sure.  You
know: if two is good, three must be better.

I don't believe that a second 'sync' will have any beneficial effect
with Linux, or any modern Unix.

Somewhat over ten years ago most filesystems added an "I was unmounted
cleanly" bit.  What you really need to do unmount the file systems,
which will have the effect of really doing what "sync" is supposed to do.

>     Still, have you tried 
>     sync; sleep 1; sync; poweroff -f

Donald Becker				becker at
Scyld Computing Corporation
914 Bay Ridge Road, Suite 220		Scyld Beowulf cluster system
Annapolis MD 21403			410-990-9993

Beowulf mailing list, Beowulf at
To change your subscription (digest mode or unsubscribe) visit

More information about the Beowulf mailing list