What mode must the Android device be in to allow ADB sideloading?

ADB sideload is a powerful feature used by advanced Android users and technicians to manually install update packages, custom ROMs, or system patches onto an Android device. It allows a user to transfer and apply a ZIP file from a computer to a phone through a USB connection, using the Android Debug Bridge (ADB) tool. To perform this process successfully, the device must be placed into a specific state known as recovery mode, which enables the update from ADB option.

Understanding ADB Sideloading

Before diving into the specific mode required, it's important to understand how ADB sideloading works. It uses a command-line interface to push update files from a computer to a connected Android device. This method is especially useful when a device cannot boot properly, or when a user prefers to manually install official or custom update packages.

Required Mode: Recovery Mode

To enable ADB sideload, the Android device must be booted into recovery mode. Recovery mode is a separate runtime environment from the main operating system, designed for device maintenance and repair. Most Android recovery environments, whether stock or custom (like TWRP), offer an option called "Apply update from ADB" or "ADB sideload."

Once this option is selected in recovery mode, the device listens for the update package being sent from the connected computer through an ADB command.

How to Access Recovery Mode

The method for entering recovery mode can vary slightly depending on the device manufacturer, but the general steps include:

1. Power off the device completely.
2. Press and hold a combination of hardware buttons (usually Power + Volume Up or Power + Volume Down).
3. Continue holding until the device logo appears and the recovery screen is displayed.

On most Android devices, once you are in recovery mode, you can navigate using the volume buttons and confirm selections with the power button.

Steps to Use ADB Sideload in Recovery Mode

Once in recovery mode, here’s how the ADB sideload process typically goes:

1. Connect the device to your PC via a USB cable.
2. In recovery mode, select “Apply update from ADB” using the volume and power buttons.
3. On the PC, open a command prompt or terminal window.
4. Use the command adb sideload update.zip to begin the transfer and installation.
5. The device will install the update and provide progress information on-screen.
6. After completion, reboot the device from the recovery menu.

Important Notes When Using ADB Sideload

• USB debugging does not need to be enabled for ADB sideload to work, since it's done in recovery mode.
• The update file must be compatible with the device and in the correct ZIP format.
• Battery level should be at least 50% to prevent interruptions.
• A failed sideload can lead to system errors or boot issues if not done properly.

Conclusion

To perform an update from ADB, your Android device must be placed into recovery mode, where the ADB sideload option is available. This special environment allows the device to receive and install updates via a direct connection to a PC. While it's a useful method for manual updates and troubleshooting, it should be used carefully to avoid installation errors or system instability.