[Discuss] Issuing the 'sync' command more than once (and a tangent on how not to run a high-tech company)

[Jerry Feldman]

On 06/16/2012 01:23 PM, Jack Coats wrote:
> It may have been folk-lore, but the 'standard procedure' where I
> worked, before shutting down a server on purpose, was, from root,
> issue 3 commands separately when we wanted an orderly shutdown, but it
> was 'urgent'.
>
>    sync
>    sync
>    halt
>
> I am sure there is some basis in history that had a basis in fact at
> the time.  Even if the 'fact' was based on 'observation' rather than
> reality.
>
See my other reply. With the old file systems, flushing and saving the
buffers was important, The halt(1) command was an immediate halt where
the Shutdown command was a script that did a sync. Generally with the
modern fast CPUs, kernels, and file systems, I don't think a sync will
buy you anything, but it will not cost you. In the olden days when you
used to do useful things, Unix systems were single CPU, and file systems
were slow. I think you remember the stone slab hard drives. What you did
not want it to halt in a partial write, then get into fsck hell.

-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
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