Mounting SD card.

[Matthias Apitz]

El día Thursday, November 15, 2012 a las 05:57:45PM +0100, Fernando Apesteguía escribió:

> On Thu, Nov 15, 2012 at 3:06 AM, Warren Block <wblock at wonkity.com> wrote:
> > On Wed, 14 Nov 2012, Mike Clarke wrote:
> >
> >> On Wednesday 14 November 2012 19:43:30 Fernando Apesteguía wrote:
> >>
> >>> If I boot the system and plug the SD card in, the green led
> >>> doesn't even switch on and there is only a /dev/da0 that I can not
> >>> mount. If I boot the system with the card plugged in, the green led is
> >>> on and there is a /dev/da0s1 device that I can't still mount because
> >>> mount_msdosfs returns an Input/Output error after some time.
> >>
> >>
> >> I think that's pretty much standard behaviour. The solution appears to be
> >> to "wake" it up with the following incantation:
> >>
> >>     dd if=/dev/null of=/dev/da0 count=0
> >>
> >> That's what works here. See the thread starting with
> >>
> >> <http://lists.freebsd.org/pipermail/freebsd-questions/2010-February/212109.html>
> >
> >
> > true > /dev/da0
> 
> That doesn't work for me, but the dd operation does. What can be the difference?

Both commands open the file /dev/da0 for:

open("/dev/da0",O_WRONLY|O_CREAT|O_TRUNC,0666)   = 3

without writing any myte to it; you can proof this with:

# truss dd if=/dev/null of=/dev/da0 count=0

and

# truss sh <<EOF
true > /dev/da0
EOF

	matthias

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