An attempt was made to mount a device that was already mounted or to unmount a device containing an active file (such as an open file, a current directory, a mount point, or a running program). This message also occurs when trying to enable accounting that is already enabled.
To unmount a device containing active processes, close all the files under that mount point, quit any programs started from there, and change directories out of that hierarchy. Then try to unmount again.
Mutexes, semaphores, condition variables, and read/write locks set this error condition to indicate that a lock is held.
The symbolic name for this error is EBUSY, errno=16.