Problem installing LineageOS

Help Fairphone 6
1

I tried installing LineageOS to my Fairphone 6. I followed the instructions as the guide said. When encountering a problem, I asked Claude, and even with its assitance I could not install it. Here’s its resume of the problems and steps taken until now. If anyone knows how to proceed it will be very helpful. Thank you in advance.**
Device:** Fairphone 6 (FP6), bootloader unlocked (confirmed via fastboot devices output — DEVICE STATE: unlocked)

Previous firmware: Android 15 (stock /e/OS from Murena)

Steps taken so far:

  1. Unlocked bootloader successfully (fastboot flashing unlock + fastboot flashing unlock_critical)
  2. Flashed the following LineageOS 23.2 (build 20260817) images via fastboot, all completed with OKAY and no errors:
    • boot.img
    • dtbo.img
    • init_boot.img
    • vbmeta.img
    • vendor_boot.img
  3. Flashed recovery.img to both recovery_a and recovery_b partitions — no errors, checksum verified and matches the one listed on the official download page (SHA256: a49d6738f239515897901fe69dcc5168d37e65b44d17fe7937310b19ed77a2ad)
  4. Have NOT yet sideloaded the main LineageOS zip

The problem:

  • fastboot boot recovery.img → fails with: Failed to load/authenticate boot image: Bad Buffer Size
  • fastboot reboot recovery → device just returns to the bootloader menu instead of booting recovery
  • Selecting “Recovery mode” from the bootloader menu manually → same, returns to bootloader
  • Selecting “Start” from the bootloader menu → same, returns to bootloader instead of booting normally

The device seems stuck in a loop back to the bootloader no matter which option I choose. It never gets stuck on a black screen or becomes unresponsive — fastboot devices still detects it every time.

My question: Is this expected behavior before sideloading the main zip, or is there a missing step / different flashing order needed for the FP6 specifically? Any help appreciated — happy to provide more logs/output if useful.

2

The install guide doesn’t say it this way, or was this in the output you got from the command?
(Just pointing out, I don’t have an FP6 and I don’t know the partition layout.)

Not every recovery image is prepared and intended for booting it with fastboot. The install guide doesn’t say to boot it with fastboot.

Not every bootloader supports this command. There are bootloaders which only support the more general fastboot reboot.
(I don’t know about FP6 in this regard.)

That’s the problem to solve.
What does fastboot --version say for you?

3

Thanks for the response.

You’re right, the “recovery_a/recovery_b” flashing wasn’t from the official guide, it was a solution proposed by Claude after “fastboot flash recovery recovery.img” (the guide’s actual command) didn’t get me into recovery.

To clarify what I actually followed from the guide originally:

fastboot flash recovery recovery.img

This completed with OKAY, no errors. Then when selecting “Recovery mode” from the bootloader menu, it just returns to the bootloader instead of booting into recovery. That’s the core issue.

fastboot --version:

fastboot version 37.0.1-15733141
Installed as /home/[my_username]/adb-fastboot/platform-tools/fastboot

Also for context, since you mentioned not knowing the FP6 partition layout, here’s the fastboot device info output, in case it’s useful:

PRODUCT_NAME - FP6
VARIANT - SM_KIMOLOS UFD
BOOTLOADER VERSION - FP6.QREL.15.176.0
BASEBAND VERSION - 15
DEVICE STATE - unlocked

Given the bootloader version string, is it possible the FP6 doesn’t have a separate recovery partition at all (i.e. “recovery-less” / recovery merged into boot, common on newer Android 13+ devices with GKI)? If so, would selecting “Recovery mode” from the bootloader menu even be expected to work, or should recovery only be reachable a different way?

4

It seems straightforward …

If there is _a and _b for recovery in FP6, does it make a difference if you do fastboot set_active other (to switch the currently active slot to the other one) and try again getting into recovery?

5

Thanks for this thread, very helpful for confirming the recovery.img step (which I did flash from the start, so that part’s covered on my end).

I’m stuck at a related but different point: after flashing boot/dtbo/init_boot/vbmeta/vendor_boot/recovery (all OKAY), selecting Recovery mode (or Start) always loops back to bootloader instead of booting. fastboot getvar all shows both slots A and B maxed out on retry-count (7) and marked slot-unbootable:yes, even after switching active slots and reflashing everything to the other slot. Anyone run into this specific retry-counter/unbootable state and know the command to reset it?

6

Flashing again should reset the count(s), says the internet.

7

Found the problem! When downloading boot.img, it got downloaded with this name but the contents of dtbo.img for some reason (same SHA256). I tried downloading it again, and after 2 tries it finally downloaded the right one. Thank you for your help!