Is it necessary to unlock bootloader before rooting Android phones?

Unlocking the bootloader is often a necessary step before rooting an Android device, but it is not always required. Here's why:

Why Unlocking the Bootloader is Typically Necessary

1. Access to System Files: Unlocking the bootloader allows you to modify the system files and partitions, which is crucial for installing custom ROMs or gaining root access. Most devices come with a locked bootloader that prevents such modifications25.

2. Security Measures: Modern Android devices have enhanced security features that prevent unauthorized modifications. Unlocking the bootloader bypasses these protections, enabling you to install custom firmware or gain root access15.

3. Device Variability: Some devices, especially those from manufacturers like Google (Pixel series) or OnePlus, support bootloader unlocking directly using fastboot commands. However, others may require specific unlock codes or exploits12.

Exceptions and Alternatives

1. Systemless Root: Some rooting methods, known as "systemless root," do not require unlocking the bootloader. These methods use techniques to gain root access without modifying the system partition, thus avoiding the need for bootloader unlocking2.

2. Exploits: In some cases, exploits can be used to gain root access without unlocking the bootloader. However, these exploits are device-specific and may not be available for all models23.

3. Manufacturer Support: Some manufacturers provide official support for unlocking the bootloader, making it easier to root devices without needing exploits2.

In summary, while unlocking the bootloader is often necessary for rooting, there are exceptions and alternative methods that can bypass this step in certain cases.