I was wondering if it's possible to make sure that some files I've deleted in the past on my mac are really gone?
I know about the option in Finder (Finder -> Secure Empty Trash...), but what if I already emptied Trash the standard way, and now want to make sure the files are fully wiped off?
Cheers.
You can erase free space using Disk Utility. (/Applications/Utilities/Disk Utility.app).
In the sidebar of Disk Utility, select “Macintosh HD” (or the drive where you’d originally stored the file). At the top of the window, select the “Erase” tab. Towards the lower left-hand corner of the window, there’s a button labelled Erase Free Space. This lets you overwrite all of the free space on the drive (which is where your deleted file currently resides). You can choose a one-pass, three-pass or seven-pass erase — hopefully that’s more than enough. And if not, I guess you can just do it multiple times.
As always with Disk Utility stuff, be a little careful. I did this a couple of years ago with a three-pass erase, something screwed up and I had to restore from a backup :(
I don't believe it's possible to erase anything securely from an SSD, unless it was only stored encrypted. The easiest way to do this for new files is with FileVault.
Update: Apparently there's something called TRIM that allows the system to securely erase files on an SSD. It may not be on by default. See this answer for more information.
I'd still use FileVault, but it looks like you don't have to. (:
