The volume containing my user folder was unexpectedly ejected, now iBooks wants the library to be in "Volume 1" instead of "Volume". Where is the preference file that tells it the location of the library?
Edit: I deleted
~/Library/Containers/com.apple.iBooksX, and moved
~/Library/Containers/com.apple.BKAgentService to the desktop then logged out. iBooks now shows the library location as
(null) and won't reset.