> For the complete documentation index, see [llms.txt](https://s0-docs.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://s0-docs.gitbook.io/docs/compliance-and-platforms/limitations/macos.md).

# macOS Validation

Development environment: all macOS/Darwin-specific code paths are structurally tested on Linux via mocked fcntl/xattr stubs. On genuine macOS deployments, the real Darwin kernel APIs are invoked. This file documents what has and hasn't been verified on actual Apple hardware.

## Fully exercised (mock-verified on Linux, code path correct by inspection)

| Capability                                   | Evidence                                                                                                                                       |
| -------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------- |
| Overwrite wipe of files / folders            | `macos/cli/tests/test_mac_cli.py` + `linux/cli/tests/test_cross_platform_eraser.py`; real bytes written, unlinked, read-back zero confirmation |
| USB / Pen drive raw wiping (`/dev/rdiskX`)   | `test_mac_cli.py::test_mac_cli_wipe_drive_main`; unmount via `diskutil`, character device raw overwrite, 32-sample verification                |
| Secondary partition wiping (`/dev/rdiskXsY`) | `test_mac_cli.py::test_mac_cli_wipe_partition_success`; volume unmount, raw block wipe, hardware cache flush                                   |
| Operating system drive safety guardrails     | `test_mac_cli.py::test_mac_cli_wipe_safety_refusal`; hard rejection of macOS boot disk (`disk0`) and active `/` mounts without force           |
| Extended attribute (xattr) clearing          | `macos_clear_attributes()` shells out to `xattr -c`; verified via mock in tests                                                                |
| F\_FULLFSYNC hardware cache flush            | `macos_full_fsync()` calls `fcntl.fcntl(fd, 51, 0)` on Darwin; falls back to `os.fsync()` on non-Darwin                                        |
| APFS CoW detection                           | `detect_macos_filesystem()` parses `mount` output; warns operator when target resides on APFS                                                  |
| Ed25519 signed certificate                   | `erase_batch_macos()` and `wipe_drive_or_partition_macos()` issue schema-compliant certificates; verified by `s0-verify`                       |
| Directory entry obfuscation                  | Filename randomized before unlinking to prevent directory-entry-level forensic recovery                                                        |
| Timestamp zeroing                            | File timestamps reset to epoch 0 before unlinking                                                                                              |

## Coded, NOT executed against the real thing

| Capability                        | What exists                                        | Why untested                                         | How to validate for real                                                                |
| --------------------------------- | -------------------------------------------------- | ---------------------------------------------------- | --------------------------------------------------------------------------------------- |
| F\_FULLFSYNC on real APFS         | Full code path via `fcntl.fcntl(fd, 51, 0)`        | No macOS machine in dev environment                  | Run on genuine macOS 12+ with internal APFS volume                                      |
| Real xattr removal on APFS        | `xattr -c` invocation                              | Requires genuine macOS with quarantine-bearing files | Download a file via Safari (creates `com.apple.quarantine`), then erase                 |
| HFS+ journal interaction          | Detection via `mount` output parsing               | No HFS+ volumes available                            | Test on macOS with HFS+ external drive                                                  |
| Time Machine snapshot persistence | APFS CoW warning issued, but snapshots not deleted | Requires `tmutil` and root access                    | Run `tmutil listlocalsnapshots /`, erase files, verify snapshot still contains old data |

## Known behavioral caveats (true on real macOS too)

* **APFS Copy-on-Write:** All writes to APFS allocate new blocks; the original data blocks persist until the filesystem reclaims free space. s0 issues an explicit CoW warning in the sanitization certificate. For guaranteed destruction, use full-volume wipe from the bootable ISO.
* **APFS snapshots:** Time Machine creates automatic local snapshots that preserve file states. Erasing a file does NOT erase it from existing snapshots. Operators must run `tmutil deletelocalsnapshots <date>` or `tmutil thinlocalsnapshots /` to purge snapshot-preserved copies.
* **System Integrity Protection (SIP):** On macOS 10.11+, SIP prevents modification of system-protected files even as root. s0 cannot erase files under `/System`, `/usr`, or `/Library` without disabling SIP from Recovery Mode.
* **Flash storage (Apple Silicon / T2 chip):** All modern Macs use soldered NVMe SSDs with hardware encryption (T2 or Secure Enclave). For NIST "Purge" assurance, use macOS Recovery → `Disk Utility → Erase` which performs a cryptographic erase (key destruction). s0's overwrite provides NIST "Clear" assurance only.
* **Sealed System Volume:** macOS 11+ uses a cryptographically sealed system volume. s0 cannot modify the SSV; this is intentional (no user data resides there).
* **FileVault 2:** Overwrite operates on the decrypted view. Original ciphertext blocks are inaccessible without the FileVault recovery key, providing defense-in-depth.
* **Spotlight metadata:** `.Spotlight-V100` may cache file metadata. Full-volume wipe is the only way to guarantee Spotlight index destruction.
* **Resource forks:** `macos_clear_attributes()` removes resource forks via `xattr -c`. Legacy HFS+ resource forks (pre-APFS) are handled by the same mechanism.


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