Item “is in use by another application”. How can I find out which one?

Question

In Finder the file VirtualBox_Uninstall.tool is greyed out.

I want to delete this file, but I'm prompted by a message that the file is currently in use:

Currently, I have no clue what is the cause of this. Therefore I want to know what other application is using it. How do I find this out?

Answer 1

The cause is usually a copy job that unexpectedly died or some process that has an open file handle on that file. You can check which process opened which files with lsof | grep "filename". This will not necessarily yield a result. If the issue isn't resolved after a logout or even a restart you still can continue at that dialog and remove the file.