I have a Samsung Galaxy A21s phone that I am trying to install Android 12 on. I have unlocked the bootloader, I go into the recovery mode and I select bootloader, however when I get there, it is just some red text saying "Entering fastboot mode..." and then it gets stuck there.

Does anyone know why this is happening, and if there is any way to fix it without carting it off to Samsung?

  • Fastboot is the bootloader. I don't know specifics of this model, but what you're describing sounds about right. Try fastboot devices.
    – gronostaj
    Commented Feb 23, 2022 at 17:37
  • @gronostaj I ran the command, it just returned an empty line and then quit. No errors or anything.
    – devjamesje
    Commented Feb 23, 2022 at 18:34
  • You need Odin or Heimdall software to flash ROMs on Samsung devices, fastboot is not used for that purpose.
    – Robert
    Commented Feb 23, 2022 at 20:06

1 Answer 1


Samsung devices only have a placeholder Fastboot mode. It doesn't actually serve any purpose. Please use Download Mode instead.

  • How do I do this then?
    – devjamesje
    Commented Feb 23, 2022 at 20:59
  • Usually, running adb reboot download while in Android should be sufficient.
    – Tri
    Commented Feb 24, 2022 at 10:54

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