On Fri, Mar 20, 1998 at 09:05:11AM -0700, Brad Davis wrote:
> > > A guy I work with says he shuts down his RH 5.0 by tpying:
> > >
> > > sync;sync;halt
> > >
> > > I shutdown my RH 5.0 with the command listed in the manual:
> > >
> > > shutdown -h now
> > >
> > > Just wondering if there is a difference between the two and is there a
> > > preferred method for the sake of the Linux Kernel.
> >
> The sysadmin in question is probably an old timer... ;^)
>
> That method was the standard under older Unices, to insure that the
> buffers were flushed to disk before shutdown.
>
> The shutdown command works nicely and avoids having to wait for the syncs
> to finish...
>From the OReilly Essential System Admin book (p131)
"Why is sync executed twice (or more)? Essentially this is a bit of UNIX
superstition. The sync command schedules, but does not necessarily
immediately perform the required disk writes, even though the unix prompt
returns immediately. Multiple sync commands raise the probability that
the write will take place before you enter another command (or turn off
the power) by taking up the time needed to complete the operation.
However, the same effect can be obtained by waiting a few seconds for disk
activity to cease before doing anything else. Typing sync several times
gives you something to do while you're waiting."
paul
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