More than often, when you try to empty the trash on Mac OS X, you get an error about a file being in use and therefore cannot be deleted. Ditto with ejecting an external disk such as a thumb drive or hard disk, you just get an ‘unable’ to eject error, but finding out which application is actually causing the error and getting it to quit or killing it can be very tedious.
What’s Keeping Me? is a freeware (donationware, actually, that category has become distinct recently) app for Mac OS X that aims at simplifying this process.
Using What’s Keeping Me is something that will not be obvious to the first time user, and this is a drawback of the program. The whole functionality of WKM is surrounded on a search based dialog, and even though its easy once you get the hang of it, the first usage is a bit complex.
Also, since WKM is a donationware, they take that to the next level by bugging you with a pop-up, that shows up everytime you start the program, which can be irritating to say the least.
Anyway, in the main dialog you see in the screenshot, you can enter the name of the disk drive/partition that you want to eject and are facing problems with, or the name of the file in the trash that you are unable to delete, and press Enter. WKM shows you a list of applications/processes that are using files from that partition or using that particular file (whichever of the 2 applies). You can then choose to either cleanly shut them down (as they have been identified) or you can choose to kill them. Both of them solve your problem, and obviously, a normal quit is preferable because it ensures that none of your data is lost. Convenient buttons for both are included in the UI.
Apart from this basic functionality, WKM also includes a slide-out tray which lists all your mounted external disks/images and contents of the trash so you can search for them easily. You can also install an Automator workflow that allows you to quickly do this process directly from Finder.
Though WKM doesn’t do much, and is not as intuitive as it should be, it can be a very useful utility when a usb drive won’t eject and is frustrating you. I recommend that you keep this program handy for such situations.