Safer Internet: Offline: Erasing Your Device


  • pencil+ Your device is running out of space
  • + Do you want others to access your files on a donated / discarded computer, phone, printer or other device?
  • + Your files may still be accessible after normal delete -- unless encrypted, or stored on SSD (solid state drive) instead of regular (spinning) hard disk
  • + Deleted / hidden information in a file might be recoverable
  • - Different meanings for "delete/erase"
  • - Have to remember to setup or check


[2] Erasing Apps -- and associated settings, and maybe data

  • To find out how much storage is used on your device: (esp. for apps, movies, videos, podcasts, music, photos, iOS backups)
  • iOS10: Settings > General > Storage&Cloud Usage > Storage > Manage Storage
  • iOS: Settings > General > iPad/iPhone Storage: Offload Unused Apps; iCloud Photo Library; individual apps
  • iOS: Settings > iTunes & App Store: Offload Unused Apps
  • macOS: [apple] > About This Mac > Storage > Manage
  • To remove not only an app, but also its settings, storage caches, etc.:
  • iOS: press down on app icon to enter move / delete ('jiggly') mode
  • tap "x" in upper left corner
  • popup: "Deleting (app) will also delete all of its data"
  • (press Home button to exit 'jiggly' mode)
  • To immediately delete related iCloud data:
  • iOS10: Settings > iCloud > Manage Storage > (device) > disable old app
  • iOS: Settings > (your acct) iCloud > Manage Storage > (app) > Delete Documents & Data
  • macOS: just dragging an app (from Applications folder) to Trash does not remove extra preference/library files
  • Use app's uninstaller (if one is provided) or an app removal utility, e.g., App Cleaner
  • [2] macOS: (select files/folders) > ctrl-click > Compress -- to reduce size of files you want to keep, but access infrequently; rename .zip if desired; delete originals when done
  • [3] macOS: Monolingual removes unused languages (and processor architectures) from System/Apps , e.g., just keep English yields ~2Gb
  • [3] macOS: (HD/SSD) : "Previous System" folder (if present: ~1-2Gb) can be deleted, but it can be very difficult/tricky to actually Empty Trash

Secure File Erasing

  • Even if you empty Trash / Recycle Bin, various utilities might be able to recover file content.
  • macOS: (≥ 10.10) use FileVault: erased file sectors are still encrypted -- thus unreadable; see Encryption section
  • macOS (< 10.10): Finder > Secure Empty Trash
  • Or, you can erase entire device -- next

Securely Erasing Device

  • ergonomicsSecurely erase drive before donating, discarding, recycling, selling or transferring your device; to be nice, re-install OS
  • [1] iOS: Settings > General > Reset > Erase All Content and Settings
  • [Refs:iOS]: "How to erase your iOS device and then set it up as a new device or restore it from backups"
  • [Refs]: "How Do I Securely Erase My Phone Before I Sell It?"
  • Trigger auto-erase if lost or stolen?
  • iOS: Settings > Passcode > (passcode) > Erase Data -- after 10 failed passcode attempts
  • iOS: Settings > (your acct) > iCloud > (device) > Find My iPhone/iPad -- allows you to erase remotely
  • [2] macOS: erase disk and install OS
  • You've already backed up anything you care about
  • Boot from Recovery Partition (option-R during Restart); or your bootable clone; for older macOS, boot from DVD or USB
  • Utilities: Disk Utility > (select drive) > Erase -- generally use Format: Mac OS Extended (Journaled) (for now, don't use High Sierra's APFS); for older macOS, and non-SSD, use option to Erase Free Space: 3 (or more times), if available
  • Utilities: Reinstall macOS/OS X
  • [Refs:Mac]: "Apple: How to reinstall macOS"
  • [Refs:macOS]: "Disk Utility's erase free space feature"
  • [Refs]: "HowStuffWorks: 10 Things to Do Before You Wipe Your Computer"

[2] File Redaction

  • very funny redactedSome source files (e.g., .doc, .pdf, .jpg) can retain layers / versions of info, i.e., metadata, or track changes; it might be recoverable via copy/paste or tools; just deleting it or overlaying an annotation may not be enough!
  • So, omit sensitive info from files in the first place: content as well as metadata such as Author, Organization
  • or, save edited document or selected screen area as an image
  • or, copy/paste selected (non-sensitive) info into a simpler format, i.e., one that removes any hidden info -- or use redaction tools (next)
  • Remove photo metadata; e.g., phone location via iOS: Photo Investigator
  • Redact a .pdf or source document to remove sensitive info -- using proper tools, i.e., Adobe Acrobat Pro; otherwise, simple annotations / changes can be selected, copied, revealed
  • [Refs]: "Redacting with Confidence: How to Safely Publish Sanitized Reports Converted From Word to PDF" (PSA from NSA)