removable devices auto umounting

Roland Smith rsmith at
Thu Mar 20 00:43:22 PDT 2008

On Thu, Mar 20, 2008 at 11:55:32AM +1000, Da Rock wrote:
> I'm just looking into the removable device issue for freebsd. I can see
> its easy enough to auto mount a removable device (although I could use
> some help getting sd/xd devices working with my card reader), but the
> removal seems to come unstuck.
> I have some barely literates on my systems, so I do need to work this
> out. Is it possible to use a forced umount to do this? What are the
> options here?

In short, no. Removal of a USB device would be forwarded to devd(8). But
since the device is no longer there at that moment, you cannot unmount
it anymore. You might get a nice kernel panic for your efforts, though. ;-)

The FreeBSD disk subsystem was simple not written with removable devices
in mind, because they didn't exist back then. Until that code is fixed
(which is hard) you _have_ to unmount before you pull the device out.

One (not bullet-proof) workaround might be to use the automounter
[amd(8)], and have it unmount very quickly after they stop being
active. This requires setting both the 'cache_duration' and
'dismount_interval' options in amd.conf(5) to very low values.
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