Securely Erasing Free Space on a Mac Hard Drive

When you delete files from your Mac’s hard drive, they are not immediately erased; instead, the space they occupied is marked as available for new data. Until new data overwrites that space, the old files can potentially be recovered using specialized software. To ensure that your sensitive data is completely irrecoverable, you can use the diskutil secureErase command in the Terminal.

Important Note: The following instructions involve using Terminal commands, which can have serious consequences if used incorrectly. Make sure to follow the steps carefully and double-check the commands before executing them.

Steps to Securely Erase Free Space

1. Open Terminal: You can find the Terminal application in the Utilities folder within your Applications folder, or you can use Spotlight to search for it.

2. Identify the Disk Name: Replace [Disk Name] in the command with the actual name of the disk for which you want to securely erase the free space. To find the correct disk name, you can use the command diskutil list. This will display a list of all connected drives, and you can identify your target drive from there.

3. Run the Command: Once you’ve identified the disk name, run the following command:

   1	sudo diskutil secureErase freespace 0 "/Volumes/[Disk Name]"

   Here, sudo gives you superuser privileges required for the operation, diskutil is the command-line utility, secureErase initiates the secure erase process, freespace specifies that you want to erase the free space, and 0 indicates the level of security (0 is a single-pass erase).

4. Enter Your Password: When prompted, enter your administrator password. You won’t see the password characters as you type – this is normal.

5. Confirm the Action: After entering the password, the Terminal will ask for confirmation. Type y and press Enter to confirm that you want to proceed.

6. Process Completion: The secure erase process will begin. The time it takes depends on the size of the free space you’re erasing. Once the process is complete, you’ll see a message indicating success.

It’s important to note that this process only erases the free space on your drive, not the existing files. If you want to securely erase specific files or the entire disk, additional steps are required.

For more detailed information and to understand the technical aspects of securely erasing a Mac hard drive, you can refer to the Backblaze blog post.

Warning: Securely erasing free space permanently deletes any recoverable data in that space. Make sure to back up any important data before proceeding.

Remember to use these commands with caution and ensure you’re performing the operation on the correct drive. If you’re uncomfortable with using Terminal commands, consider seeking assistance from someone with more technical expertise.