From nookDevs

Part of the NookColor portal

The Nook Color automatically defaults to automounting both the internal storage and SD card (if installed) when you plug it into your computer. This is great if your primarily use case for plugging it in is downloading books, but if you're reading this you are probably more likely to be tinkering or using adb. In that case, it could be useful to temporarily or permanently disable the automount functionality. Both can be reverted easily.

Temporarily Disable Automounting

If you want to disable the automounting temporarily and do not need it to persist across reboots, such as when doing some debugging using adb, use the following:

host$ adb shell setprop persist.service.mount.umsauto 0

Using a terminal emulator:

$ su
# setprop persist.service.mount.umsauto 0

Using the NookColor and NookColor Tools:

NookColor Tools -> All Settings -> Development -> Auto Mount (uncheck)

Note: If you do not have NookColor Tools, there is currently no way to manually enable the USB mass storage device without re-enabling it via adb or in a terminal.

Note: Disabling automount MAY make your battery level indications not work right when plugged in.

To re-enable the default behavior, run the following command:

host$ adb shell setprop persist.service.mount.umsauto 1

Using a terminal emulator:

$ su
# setprop persist.service.mount.umsauto 1

Using the NookColor and NookColor Tools:

NookColor Tools -> All Settings -> Development -> Auto Mount (check)

Permanently Disable Automounting

To disable automounting permanently, do the following:

host$ adb shell busybox echo -n 0 > /data/property/persist.service.mount.umsauto

Note: This must be done using busybox as described, otherwise you will get a newline character at the end and it not work and possibly do bad things.

Note: I have seen this not work at least once, if anyone else notices the same, please edit and let us know. This information might not be accurate yet if so.  :(

Note: I have also seen this not work. If we can comment out/delete the line "setprop persist.service.mount.umsauto 1" in "/init.rc". The problem I run into is that the change is lost on reboot. -hoban

Note: /data/property/persist.service.mount.umsauto seems to be written/replaced at boot on my NookColor. - Rexxin

To undo this change:

host$ adb shell rm /data/property/persist.service.mount.umsauto

You should be able to temporarily re-enable it using the setprop to 1 using the example in the Temporarily Disable Automounting section.