On LineageOS 23.2, how to write the Magisk patched `boot.img` not in `/sdcard/` to avoid a third party app altering it?
Jul 18, 5:48pm

On LineageOS 23.2 (or any Android device), if you want to avoid storing the Magisk-patched boot.img in /sdcard/ (internal storage) to prevent third-party apps from accessing or modifying it, you have a few secure alternatives:

1. Store in /data/local/tmp/

  • This directory is root-accessible and not directly exposed to most third-party apps.
  • Steps:
    1. Patch boot.img using Magisk.
    2. Push the file to /data/local/tmp/ via ADB: 
      bash
      adb push magisk_patched.img /data/local/tmp/
    3. Flash it manually in a custom recovery (TWRP) or via fastboot: 
      bash
      fastboot flash boot /data/local/tmp/magisk_patched.img
      (Note: Some recoveries may not allow direct flashing from /data/local/tmp/. If so, use adb pull to retrieve it temporarily.)

2. Use a Custom Recovery (TWRP)

  • TWRP allows you to sideload or manually select the boot.img from an external source (e.g., USB OTG, microSD card).
  • Steps:
    1. Copy magisk_patched.img to a USB drive or microSD card.
    2. Boot into TWRP → Install → Select Storage (USB-OTG/SD card) → Flash the image.

3. Use fastboot Directly

  • If you have unlocked bootloader, you can flash the patched boot.img directly via fastboot without storing it on the device: 
    bash
    fastboot flash boot magisk_patched.img
    (This avoids storing the file on /sdcard/ entirely.)

4. Encrypted Storage (Advanced)

  • If your device supports FBE (File-Based Encryption), you can store the file in an encrypted directory (e.g., /data partition) that requires user authentication to access.
  • Limitation: Requires root and may not be accessible to all flashing tools.

5. Temporary ADB Push + Flash

  • Push → Flash → Delete (for paranoid users):
    1. Push the file: 
      bash
      adb push magisk_patched.img /data/local/tmp/
    2. Flash it via recovery or fastboot.
    3. Delete it immediately after flashing: 
      bash
      adb shell rm /data/local/tmp/magisk_patched.img

Key Notes:

✅ Best for Security: fastboot flash boot (no storage on device) or TWRP + USB OTG. ⚠ Avoid /sdcard/: Third-party apps with storage permissions can access/modify files here. 🔒 Root Required: /data/local/tmp/ and encrypted storage require root access.

Recommendation:

  • For most users: Use fastboot flash boot (no file stored on device).
  • For recovery users: TWRP + USB OTG (no /sdcard/ involvement).
Jul 18, 5:48pm

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