Android Fastboot

Android Fastboot Operations

⚠️ DANGER ZONE - Fastboot operations write directly to device partitions. Wrong images or interrupted operations can brick devices. Always verify:

1. Correct device (check fastboot getvar product)
2. Correct images for exact device model
3. Bootloader is unlocked (for flashing)
4. Battery > 50%

Entering Fastboot Mode

# From ADB (device running)
adb reboot bootloader

# Hardware buttons (most devices)
# Power + Volume Down (hold until fastboot screen)

Basic Commands

fastboot devices                    # List connected devices
fastboot getvar all                 # All device variables
fastboot reboot                     # Reboot to system
fastboot reboot bootloader          # Stay in bootloader
fastboot reboot recovery            # Boot to recovery
fastboot reboot fastboot            # Boot to fastbootd (Android 10+)

Check Before Flashing

# ALWAYS run these first
fastboot devices                    # Verify connection
fastboot getvar product             # Verify device model
fastboot getvar unlocked            # Must be "yes" for flashing
fastboot getvar current-slot        # Know current A/B slot
fastboot getvar battery-level       # Should be > 50

Bootloader Unlocking

Google Pixel

# 1. Enable OEM unlocking in Developer Options
# 2. Boot to fastboot
adb reboot bootloader

# 3. Unlock
fastboot flashing unlock

# 4. Confirm on device with volume keys + power
# WARNING: This wipes all data!

Other Manufacturers

Check Unlock Status

fastboot getvar unlocked            # yes/no
fastboot getvar device-state        # locked/unlocked
fastboot getvar unlock_ability      # Can be unlocked?

Flashing Partitions

Individual Partitions

fastboot flash boot boot.img
fastboot flash recovery recovery.img      # Non-A/B only
fastboot flash dtbo dtbo.img
fastboot flash vbmeta vbmeta.img

# Disable verification (for custom ROMs)
fastboot flash --disable-verity --disable-verification vbmeta vbmeta.img

Bootloader & Radio (Extra Careful!)

# These can hard-brick if wrong!
fastboot flash bootloader bootloader.img
fastboot reboot bootloader    # REQUIRED after bootloader flash

fastboot flash radio radio.img
fastboot reboot bootloader    # Recommended after radio flash

Temporary Boot (No Flash)

# Test before committing - reboots to normal after restart
fastboot boot recovery.img
fastboot boot patched_boot.img

A/B Slot Devices

Modern devices have two copies of each partition (A and B).

# Check current slot
fastboot getvar current-slot        # Returns: a or b

# Set active slot
fastboot set_active a
fastboot set_active b

# Flash to specific slot
fastboot flash boot_a boot.img
fastboot flash boot_b boot.img

# Flash to both slots
fastboot --slot=all flash boot boot.img

Dynamic Partitions (Android 10+)

Large partitions (system, vendor, product) live inside a "super" partition.

Fastbootd Mode

# Enter userspace fastboot
fastboot reboot fastboot

# Check if in fastbootd
fastboot getvar is-userspace        # Should return: yes

Flash Dynamic Partitions

# Must be in fastbootd mode!
fastboot reboot fastboot

fastboot flash system system.img
fastboot flash vendor vendor.img
fastboot flash product product.img

Virtual A/B Snapshots

# Check snapshot status
fastboot getvar snapshot-update-status

# Cancel stuck update (CAREFUL!)
fastboot snapshot-update cancel

Recovery Operations

Enter Recovery

adb reboot recovery
# Or: Power + Volume Up (varies by device)

ADB Sideload

# 1. In recovery, select "Apply update from ADB"
# 2. Run:
adb sideload update.zip

Flash Custom Recovery (TWRP)

# Test first (temporary boot)
fastboot boot twrp.img

# If it works, flash permanently
# Non-A/B devices:
fastboot flash recovery twrp.img

# A/B devices (recovery in boot):
fastboot flash boot twrp.img

Magisk (Root)

Installation

# 1. Extract boot.img from your firmware
# 2. Transfer to device, patch with Magisk app
# 3. Pull patched image
adb pull /sdcard/Download/magisk_patched_*.img

# 4. Flash patched boot
fastboot flash boot magisk_patched_*.img

# 5. Reboot
fastboot reboot

Useful Magisk Commands (after rooted)

adb shell su -c "magisk --version"
adb shell su -c "resetprop ro.debuggable 1"

Factory Reset / Wipe

fastboot erase userdata             # Wipe user data
fastboot erase cache                # Wipe cache (if exists)
fastboot -w                         # Format data + cache

# Full flash with wipe
fastboot -w flashall
fastboot -w update image.zip

Danger Levels

Brick Prevention

Never:

• Flash images from different device models
• Interrupt a flash operation
• Lock bootloader with custom ROM installed
• Flash bootloader/radio without matching versions

Always:

• Verify device with fastboot getvar product
• Keep stock images available for recovery
• Use fastboot boot to test before fastboot flash
• Maintain battery > 50%

Recovery from Soft Brick

# 1. Enter fastboot (Power + Vol Down)
fastboot devices

# 2. Flash stock boot
fastboot flash boot boot.img

# 3. For dynamic partitions
fastboot reboot fastboot
fastboot flash system system.img
fastboot flash vendor vendor.img

# 4. Wipe if needed
fastboot -w

# 5. Reboot
fastboot reboot

For hard bricks (no fastboot access), you need EDL mode (Qualcomm) or manufacturer service tools.

Quick Reference