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Module 06IntermediateWeek 5 · 17 min read

ADB, Fastboot & Recovery Mode

The three doors into an Android device

Module 6 of 1242%
01

Welcome

Welcome to Module 6. From here on you work at the command line. These three interfaces solve the majority of software faults without any paid tool.

02

Learning Objectives

  • Use core ADB commands confidently.
  • Boot into and operate Fastboot.
  • Navigate stock recovery safely.
  • Pull logs from a failing device.
  • Sideload an OTA package.
03

Prerequisite Knowledge

  • Beginner level complete

If any of these are unfamiliar, review the Foundation level first.

04

Vocabulary

ADB
Android Debug Bridge — talks to a booted or recovery-mode device.
Fastboot
A bootloader-level protocol for writing partitions.
Sideload
Applying an update package over ADB from recovery.
logcat
The live Android system log.
RSA authorisation
The on-device prompt that authorises your workstation for ADB.
05

Why This Matters

A boot loop that logcat explains in thirty seconds is a repair. The same boot loop without logs is a guess that costs the customer their data.

06

Lesson Content

Lesson 1Core ADB commands6 min

adb devices, adb reboot bootloader, adb shell, adb pull, adb logcat, adb sideload.

Unauthorised in the device list means the RSA prompt has not been accepted — a locked screen blocks it.

Lesson 2Fastboot basics6 min

fastboot devices, fastboot getvar all, fastboot flash boot boot.img, fastboot --set-active=b.

getvar all tells you the product, slot and unlock state before you write anything.

Lesson 3Working in recovery5 min

Stock recovery offers wipe cache, factory reset and sideload. Wipe cache first; it is non-destructive and fixes a surprising number of loops.

07

Visual Explanation

Device boots to Android?  ── yes ──► ADB
        │ no
        ▼
Reaches recovery?  ── yes ──► sideload / wipe cache
        │ no
        ▼
Reaches fastboot?  ── yes ──► flash boot / switch slot
        │ no
        ▼
   EDL / download mode
Which door do you need?
08

Real-World Example

A customer says: “It reboots every 30 seconds after an update.”

First non-destructive action?

Boot recovery and wipe cache, then capture logcat during the next boot attempt.

Possible causes

  • Corrupt dalvik cache
  • Failed OTA patch
  • Bad app on system start
09

Technician Tips

Technician Tip

adb logcat > log.txt captures the crash even when the screen dies.

Technician Tip

Always run fastboot getvar all before flashing — it prevents wrong-device disasters.

Did You Know?

adb sideload can apply a full official OTA without unlocking the bootloader or losing data.

10

Common Mistakes

Common Mistakes

  • Running fastboot commands on the wrong slot
  • Flashing an image built for another variant
  • Factory resetting before capturing logs
11

Safety Notice

Safety Notice

  • Never unlock a bootloader without consent — unlocking wipes the device.
  • Capture logs before any destructive step.
12

Hands-on Practice

Exercise 6 — Log a boot

  1. Connect a test device
  2. Run adb logcat and save to file
  3. Reboot and capture the boot sequence
  4. Identify three services starting
13

Knowledge Check

Question 1 of 2

Which command reveals the active slot?

14

Mini Project

Mini Project — Command reference card

  1. Build a one-page ADB/Fastboot reference
  2. Group by scenario, not alphabetically
  3. Test every command on a real device before publishing it
15

Reflection

  • Which command did you fear most, and why?
  • What would you check before pressing enter?
16

Module Summary

Today you learned:

  • ADB
  • Fastboot
  • Recovery
  • Sideload
  • Log capture
17

Resources

18

Assignment

Write a scenario-based command guide covering five real faults and the exact commands you would run.

Intermediate - Exploit and bypass utilities — stage assignment

Register a test device's ECID and bypass the hello screen on a supported iPhone model.

19

Tools for this Stage

Now you work below the operating system: exploit loaders and account-bypass utilities used for Hello-screen and iCloud/FRP scenarios on eligible devices.

Usbliter8 Exploit Tool

Windows/macOS - iOS (A7-A11)

checkm8-class USB exploit loader for A7 to A11 iDevices

What it does. Loads an unpatchable bootROM exploit over USB on eligible chipsets to allow low-level operations such as passcode work, Hello-screen bypass and diagnostics that iTunes cannot perform.

Why it matters. It gives you a legitimate low-level entry point on supported models, which is often the only route to service a locked but customer-owned device.

Risks & precautions

  • Use only on devices whose ownership you have verified.
  • Not all sessions survive reboot - work while the exploit is loaded.
  • Newer chipsets are patched and will fail; forcing it wastes time.

Best practices

  • Confirm chipset eligibility before quoting the customer.
  • Log ECID and serial for every session.
  • Keep the workstation off sleep during the exploit window.
⇩ checkm8 background & chipset list

Assignment

Load the exploit on a supported test device, record ECID, and exit cleanly without changes.

GB Bypass Tool

Windows - iOS / Android

Hello-screen and Google-account bypass on owner-verified devices

What it does. Automates the sequence of exploit load, ramdisk boot and account-state edit used to bypass Setup-Assistant lock screens on devices you have verified as customer-owned.

Why it matters. Locked screens after a legitimate reset are one of the most common bench requests. A single tool with a clear log removes guesswork.

Risks & precautions

  • Never operate on devices without documented ownership - this is a legal red line.
  • Some bypass states do not survive erase or update.
  • Cellular functions may be limited on certain bypass modes.

Best practices

  • File a signed ownership declaration before starting.
  • Explain to the customer which functions may be limited afterwards.
  • Update the tool only from the vendor's channel.
⇩ Vendor / official portal (open only if trusted)

Assignment

On a customer-owned test device, complete a bypass and write the state (tethered / untethered, signal, iCloud) into your log.

See all tools by stage ↗
20

Module Test

Complete the 2-question knowledge check above plus the assignment. Passing score: 80%.

21

Capstone

Capstone 2 — Intermediate

Device: Samsung Galaxy A15

Fault: Boot loop after a failed update

  • Diagnose using recovery and logcat
  • Choose the correct firmware package
  • Install and verify drivers
  • Flash with HOME_CSC to preserve data
  • Verify the repair over a 30-minute soak test
  • Write customer-facing repair notes