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DIRTY_FLASH.md

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Dirty Flash — Update ROM without wiping data

A dirty flash updates your ROM while keeping all your apps, settings, and data intact. Faster than clean flash but riskier.

When to dirty flash

✅ Safe: point releases (12.0 → 12.1), same ROM branch, same device

❌ Risky: major versions (11 → 12), ROM switches, different base version

Before you start

# Backup critical data
adb backup -apk -shared -all -f backup.ab

# Create TWRP backup
# (in recovery: Backup tab)

Dirty flash procedure

1. Download new ROM zip for your device
2. Reboot to recovery (TWRP or LineageOS Recovery)
3. Flash the new ROM zip
4. **Skip wiping data/cache** — go directly to install
5. Optional: Flash Magisk (if using root)
6. Reboot

TWRP method

Recovery → Install → select ROM.zip → Swipe to confirm
(don't wipe, don't factory reset, just install)
→ Reboot

LineageOS stock recovery

Recovery → Apply update from ADB
adb sideload ROM.zip

Potential issues after dirty flash

Issue Fix
Bootloop Wipe /cache and /dalvik-cache, reboot. If still broken, clean flash.
Slow boot Run adb shell pm compile -r bg-dexopt to recompile packages
App crashes Clear app caches: adb shell pm clear <package>
WiFi/BT broken Reboot, check system logs with adb logcat
Google Play broken Clear Play Services: adb shell pm clear com.google.android.gms

Recovery in case of disaster

If dirty flash breaks your system:

Option 1: Go back (if A/B device)

adb reboot bootloader
fastboot getvar current-slot
fastboot set_active a  # or b (opposite of current)
adb reboot

Option 2: Clean flash from recovery

# Boot to recovery and select Factory Reset
# Then install ROM again

Option 3: Return to stock firmware

adb reboot bootloader
fastboot flash system system.img
fastboot flash -w
fastboot reboot

Pro tip: Dirty flash with Magisk survival

LineageOS A/B users can update without losing Magisk:

# In recovery:
1. Install ROM zip
2. Install Magisk zip
3. Boot (Magisk patched the new boot.img automatically)

Safety checklist

  • Backup important data
  • Check device codename matches ROM
  • Verify ROM release notes for known issues
  • Keep TWRP backup available
  • Have original firmware available
  • Don't dirty flash across major versions

Golden rule: If you're unsure, do a clean flash. Data is replaceable; broken device is not.