diskutil secureErase freespace 4 /Volumes/Macintosh HD
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* You can use “4” for the wipe level, or select a different option from the following list:
* 0 – Single-pass zero-fill erase.
* 1 – Single-pass random-fill erase.
* 2 – US DoD 7-pass secure erase.
* 3 – Gutmann algorithm 35-pass secure erase.
* 4 – US DoE algorithm 3-pass secure erase.
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