The Samsung Galaxy S21 5G SM-G991U comes with a version of the Android 11 operating system out of the box that has the bootloader locked. Samsung didn’t use to lock its smartphone bootloaders; however, in recent years it has become common with some of their more popular models. Thankfully, Samsung hasn’t made it a requirement to unlock it via Fastboot or the command line; instead, you can do it directly from the GUI. It still means you will void the warranty on the Samsung SM-G991U smartphone should you go ahead and unlock the bootloader though. Unlocking it means you can get access to custom firmware. However, you can install official firmware with the locked bootloader still.
The following tutorial demonstrates how to OEM unlock the Samsung SM-G991U bootloader.
Smartphone operating systems come with a bootloader (also known as a boot manager or bootstrap loader). The bootloader is the program responsible for booting the operating system. Sometimes this bootloader is locked by default, while other times it can come unlocked already. With an unlocked bootloader, you can install custom firmware. In today’s world, this is most often relevant to the Android operating system, and that certainly is the case when it comes to Samsung smartphones in particular. Samsung smartphones don’t come with the bootloader unlocked, but they also don’t make bootloader unlocking an arduous process. This is excellent news for those who do wish to install custom firmware because some manufacturers require the use of software exploits to unlock bootloaders.
How to Unlock Samsung SM-G991U Bootloader
You can unlock the bootloader on most Samsung smartphones by booting into Download Mode and selecting the option to unlock the bootloader, called Device Unlock Mode, from the menu. Here is how to do that:
Note: You need to connect your Samsung SM-G991U smartphone to the internet via Network & internet > Internet. Alternatively, you can search for the WiFi network you want to connect to by using the search field via the Settings Menu.
1. Press the Power button to turn on the Samsung SM-G991U device.
2. Enable the Developer Options Menu on the Samsung SM-G991U device. See this tutorial for enabling the Developer Options menu on Samsung smartphones: How to Unlock Developer Options Menu and Enable USB Debugging Mode on Android.
Warning: Unlocking the bootloader usually causes the data to be wiped on the smartphone. So make sure you have backed up your data before continuing.
3. Boot the Samsung SM-G991U smartphone into Download Mode. See this tutorial for booting a Samsung smartphone or tablet into Download Mode: How to Enter Download Mode on Samsung Smartphones and Tablets.
4. From the Warning screen that lets you know that a custom OS can cause critical problems on the smartphone and its installed applications, long-press the Volume Up button.
5. From the Unlock Bootloader screen that tells you if you unlock the bootloader you will be able to install a custom operating system on the smartphone, press the Volume Up button.
Note: If the device shows you a message letting you know that all data will be deleted before the bootloader can be unlocked, press the button to confirm you understand this.