Howto install Calyx OS on FP4

I got a new FP4 and first thing after registration was to wipe the system and install Calyx OS. For anyone out there who wants to try it, I’d like to share my experience, since at the time of this writing, the CalyxOS easy device flasher does not support FP4 yet and installation can be a bit scary. So this is exactly what I did.

Warning and Disclaimer: While this worked for me, there is no guarantee that this can be reliably reproduced. So proceed with caution. I am not responsible for any damages that might occur by following this how to. If you brick your phone, that’s your own responsibility, do not blame me. You have been warned!

Additional Warning: This will wipe all user data. So make backups.

I used Arch Linux with android-sdk-platform-tools 33.0.1-1 (aur) and android-udev 20220102-1 installed.



  1. Go through Fairphone setup and install all available updates

  2. Enable Developer Options. Settings → About Phone → Hit ‘Build Number’ until activated

  3. Get Bootloader Unlocking Code for Fairphone 3 - Fairphone and follow instructions to enable OEM unlocking in Developer Options

  4. in Developer Options enable USB Debugging

  5. Connect phone to PC via USB and run adb reboot bootloader. From now on, just keep it connected until we are finished. Phone reboots into fastboot mode. If adb cannot find your device, try different USB cables and ports. Also make sure that your phone’s USB usage is set to “Transfer Data”. Try adb kill-server; adb start-server, reconnect and try again. Allow access on the phone from your computer.

  6. When the phone has rebooted into fastboot mode run fastboot flashing unlock. Confirm with Vol Down + Power. This will wipe your data. You might need sudo if udev rules are missing. If fastboot cannot find your device, again try different cables and ports, it seems to be very picky. The phone erases all data and reboots into FPOS. Skip through setup and again enable Developer Options and USB Debugging. Make sure OEM unlock is still enabled.

  7. Again run adb reboot bootloader.

  8. Now from the extracted FP4-sp2a.220505.002 directory run ./
    This is the scary part, this will wipe your OS! For me, there were a lot of errors that said FAILED (remote: 'Flashing is not allowed for Critical Partitions') but it still worked out in the end, so bear with me. The device will reboot a couple of times.

  9. When the script finished my Phone tried to reboot twice and then went to recovery mode with the following error:
    Cannot load Android system. Your data may be corrupt. If you continue to get this message, you may need to perform a factory data reset and erase all user data stored on this device.

  10. With Vol Down select Factory Data Reset and confirm with Power. System will again erase all data and finally reboot into CalyxOS.

  11. If boot was succesfull, skip through setup and again enabled Developer Options and USB Debugging. We will wipe data one last time.

  12. adb reboot bootloader

  13. Relock the bootloader: fastboot flashing lock. This is strictly not required but highly recommended. Also if you want to have SafetyNet Attestation, you must relock your bootloader. Again, this will erase all user data. Beware: there have been reports of unrecoverable bootloader loops after relocking, this can brick your phone. Before relocking, make absolutely sure, that your phone can boot into Calyx and that OEM Unlock is enabled in Developer Options. Double check if unsure!

  14. Watch reboot into CalyxOS and enjoy your new degoogled privacy OS!

Good Luck!


You can use fastboot flashing unlock_critical before starting the installation to get rid of those errors.
It works without that but your critical partitions won’t get flashed. So if those have been changed from the stock ones by the Calyx devs (AFAIK they haven’t) this might lead to problems in the future.
Better safe than sorry though :slightly_smiling_face:


I wonder if/why in your case OEM unlock was enabled after flashing and booting CalyxOS. It wasn’t and still isn’t in my case, and I think I followed essentially the same procedure. The only differences I am aware of: I did unlock_critical and started with

I’ve seen this on some other threads (I think about installing /e/?), but it seems this might be correlated to some of the boot loop bricks that have occured. On the CalyxOS install instruction page there is also no mentioning of unlock_critical and on their Matrix testing channel they said to stick exactly to their instructions until this boot loop thing can be figured out. So that’s why I decided not to unlock_critical. But sure, I don’t know what consequences that will have down the road.

On the Matrix testing channel I read that there could have been a bug that messed with lock/unlock in earlier images that has been fixed in the latest image. So maybe that’s what could have happened to you?

Possibly. But if so, re-flashing with the latest image does not fix things. When I tried this at first I was happy because immediately after flashing get_unlock_ability was 1 - but after booting into CalyxOS OEM unlocking still was disabled/greyed and get_unlock_ability again was 0.

OK, I’ll wait if someone finds a safe way to fix this. :grinning:

I know it’s not mentioned in their instructions and they weren’t clear about it when people asked them on Matrix in the past, but they are shipping critical partitions and there is code in to flash those. What would be the point of including those if you don’t want them to end up on the device? :man_shrugging:

Fairphone had to be made aware of that command as well and they subsequently changed the documentation to include it. So if you follow the official Fairphone guide to unlock the bootloader, you’ll end up with critical partitions unlocked as well.

As I was saying, those critical partitions are still the same across the different custom ROMs (and stock FPOS) as far as I can tell, so you probably don’t have to change something on your newly installed system because you already were on the right version, but that might not be the case in the future.


So one thing that apparently does not work when you haven’t used unlock_critical is automatic OTA update. At least the first one. According to information from the Matrix channel, you need to sideload the first OTA update. But the next should be fine and work as expected.

To sideload the Calyx OTA update do the following

  • download the full ota-update from

  • make sure that USB Debugging is enabled in Developer Options

  • connect you FP4 to your PC and run adb reboot recovery

  • when the FP4 has rebooted, the android lying down will appear and on the bottom of the screen it should say “no command”

  • press Power & Vol +. This should open the recovery menu

  • with Vol - select Apply update from ADB. Confirm with Power

  • on your PC run adb sideload Your PC will show a percentation progress, your phone will show some status messages. This will take a few minutes

  • when finished, the menu will appear. Select reboot now

Phone should reboot into updated Calyx OS