How To: Taking screenshots of Time Machine

Last week, I worked on a TUAW post about ways people talk themselves out of using Time Machine. At one point in the post I needed to show a screenshot that demonstrated how to remove individual backups.

Unfortunately, I quickly discovered that you cannot perform normal screenshots while engaged in the Time Machine interface.

So what I did was step back and mess around a bit at the OS X command line to see if I couldn't get around that problem. Be warned that this solution uses the Unix terminal. If you are unfamiliar with that utility app, you'll probably want to skip the rest of this post.

The screencapture utility can be found in /usr/sbin. It enables you to grab images from the screen and save them either to a file or, as I wanted to do, the clipboard. What I needed to do was set the screen capture in motion, enter Time Machine, set up my shot and only then have the screen grabbed on my behalf.

Fortunately, screencapture offers a time offset that allows you to delay the shot however many seconds into the future via the -T option. You supply a number, in my case I used 20 seconds, and then have time to set up. Once the shot is captured, you hear a camera shutter sound and you can retrieve the image you've created.

The exact options I used were as follows. The -c option stores the image to the system pasteboard (commonly called the clipboard, hence the "c"). The -m option shoots only the main screen (I use multiple monitors).

% screencapture -c -T20 -m

Together, this provided me a sweet solution for providing visual access to a screen that I couldn't normally capture.