When plugging in an external USB storage medium, such as an
USB stick, the Linux 2.4 kernel generates a hotplug event and,
since a certain commit of mine, a syslog message describing it.
The default hotplug scripts then mount the medium if possible.
However, when the medium is plugged in during boot (dubbed
“coldplug”), no such event is generated.
It is possible to scan for and mount any media in /etc/rc.local
but they will not be registered with the hotplug system then,
and thusly, subsequent events regarding this medium (e.g. an
unplug event) will not correctly umount the device, because the
USB bus/device ID information is not available to people just
scanning /dev/discs/ for device nodes.
The optimum solution would probably be to patch the kernel to
generate hotplug events for coldplugged devices as well, just
like it already does for the network interfaces (if you don't
believe me, read dmesg). Is there such patch we could integrate?
Furthermore, someone should evaluate whether this applies to
the Linux 2.6 kernel too.
