No "task complete" message after securely erasing free space. Did it work or not?

Originally, I used Disk Utility to erase free space (7 passes), but received an error message saying "unable to create temporary file" (I have 439GB of free space, so I don't know why I received this message). I then attempted the same thing, but in recovery mode this time. It takes forever of course (at least 11 hours), so I didn't exactly sit there and stare at it. I checked it when I got home last night and Disk Utility looked the same as when I first opened it. There was no error message, but there was also no message saying "erase space complete", or whatever it should say. Does that mean it didn't work? I've never used Disk Utility for this before, so I'm not sure whether there is supposed to be a message.