If you have plug encrypted removable media into a recent GNU/Linux distribution it will probably try to automount it for you.
So far, so hoopy.
However a recurring class of bugs in the hot plug logic is failure to tear down the encrypted device mapper when the media is removed without unmounting it first.
It results in a message something like this:
Naturally this is a bug in your distribution but it is one that tends to regress as the desktop stack is developed so knowing how to workaround will do you no harm at all.
I generally use:
sudo cryptsetup luksClose udisks-luks-uuid-d9fb9d0d-74e6-49b1-94d3-7edc083f04c0-uid80377
Note: gnome-shell-3.2 will prompt you for a password but doesn’t issue an error message if the automount fails. If you want to see the error message (and hence the name of the mapping) open the file manager and try to mount the encrypted partititon from there instead.
Although I couldn’t really be bothered you could easily write a script to automatically identify encrypted device mapping that aren’t being used and undo them by getting a script to look at the output of
ls -al /dev/mapper. Probably it would be best to look for devices that have a mapping but are not mounted.