Stuck Installing on Galaxy A21s - Boots to Stock Recovery After Successful Flash

/e/OS Devices Samsung
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Hello everyone,

I’m trying to install /e/OS on my Samsung Galaxy A21s but I’m stuck. After what appears to be a successful recovery flash, the device always boots into the stock
Android recovery instead of the /e/OS recovery.

Device & Version Information:

  • Phone Model: Samsung Galaxy A21s (SM-A217F/DSN)
  • Stock Android Version: Android 12 (as required by the installation guide)
  • /e/OS Build: e-3.1.1-a15-20250829521751-community-a21s
  • /e/OS Recovery: recovery-e-3.1.1-a15-20250829521751-community-a21s.img
  • PC OS: Linux
  • Flashing Tool: Heimdall v2.0.2
  • “Secured by Knox” appearing on boot screen

Summary of the Problem:
No matter which method I try, after flashing the /e/OS recovery with Heimdall, the phone will only boot into the stock Android recovery menu, not the /e/OS menu.

Detailed Steps I’ve Taken:

  1. Unlocking the Bootloader:

    • Initially, the “OEM Unlocking” option was not visible in Developer Options.
    • I successfully used the “date trick” (setting the date back, disabling auto-updates) to make the option appear.
    • I enabled “OEM Unlocking” and used Download Mode to unlock the bootloader. After this first unlock, I saw a “Custom binary blocked by OEM lock” error, so I
      performed the unlock process a second time.
    • The second bootloader unlock was fully successful. After going through the setup wizard (with Wi-Fi connected), I confirmed in Developer Options that “OEM
      unlocking” was enabled and greyed out, which I believe is the correct state.

  2. Flashing the Custom Recovery:

    • I booted the phone into Download Mode.
    • I used the command: heimdall flash --RECOVERY recovery-e-3.1.1-a15-20250829521751-community-a21s.img --no-reboot
    • The flash completes successfully every time, with RECOVERY upload successful shown in the log.

  3. Attempting to Boot into Recovery (All Failed):

    • Method 1 (Button Combo): Immediately after the flash, I unplugged the USB and held Volume Up + Power. The phone reboots, but always into the stock Android
      recovery.
    • Method 2 (Button Combo with Release): I tried again, this time releasing the buttons as soon as the Samsung logo appeared. The result was the same: stock
      Android recovery.
    • Method 3 (ADB Command): I booted the phone into the normal Android OS, enabled USB Debugging, and authorized my computer. I then used the command adb reboot
      recovery. The command executes without error, the phone reboots, but it still goes into the stock Android recovery.

It seems like even with an unlocked bootloader, some security feature on the device is preventing the custom recovery from running and is forcing a fallback to the
stock recovery.

Has anyone else with an A21s experienced this? Is there a known workaround? Could the problem be Knox?

Thank you for your help.

Regain your privacy! Adopt /e/OS the deGoogled mobile OS and online servicesphone

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Hello, I will try with Odin and twrp software, at some point you have to format to clean, and remember to check “replace Recovery mode with E/OS” at the end of the OS installation. I had not checked this box and I had the same problem as you with restarting in Recovery Mode.

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Either this was actually a fail in some way or you can improve the button combo (which is known to vary on modern devices). Perhaps try a variation on

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