Suck in boot loop after shutting off phone during OTA update

coolsnoo

Hi everyone,
I have a Pixel 4a 5G that is stuck in a boot loop and I'm pulling my hair out trying to figure out how to recover it. Any suggestions would be much appreciated.

Basically, I installed GrapheneOS per the official instructions and everything worked just fine. The OS worked as expected and there were no errors during the install. I'm confident everything here went fine. I've turned off and back on the phone multiple times and it worked fine.

However, at some point I went on WiFi and GrapheneOS started downloading and installing an update. As this was happening in the notification bar, I figured the case was handled that things wouldn't mess up if I were to shut down the phone normally through the Power Menu (so not any hard shutdown or anything). However, after turning the phone back on, I was greeted with a perpetual boot loop.

It shows the "your device is loading a different operating system" message, then a Google logo, then it reboots back to the different OS message and goes through that cycle endlessly until the battery is drained. Occasionally I am able to get it to show the GrapheneOS logo by tapping hard on the screen with two fingers during boot up, but it only shows this for a second then boot loops as usual.

My phone is OEM unlockable but the setting is in the developer options in settings which I cannot reach and is currently in the OEM locked toggle position. Is there any way to set OEM Unlock to true without using the UI (which I can't access)?

Here's what I've tried to recover:

Android Flash Tool to recover original firmware - won't let me proceed with error: Request is missing required authentication credential.
Apply Update from ADB via GrapheneOS Recovery - tried GrapheneOS firmware zip, Android factory firmware from Google, Android OTA update firmware package from Google - none of these worked, they all give me "Signature verification failed" (among other things like "footer is wrong" and "error: 21"). I tried multiple USB cables.
Wipe data/factory reset from GrapheneOS Recovery - still stuck in boot loop, only thing that changed is that Google logo on boot went from black background to white background for some reason...
Various other things I found from googling on the internet, for example: this and this

There's a Rescue mode from the first recovery screen that sounds promising, but I don't know what to do with it and I can't find any documentation on how I'd use it to rescue my phone, but I very well may just not be Googling for the right phrase here.

Basically, without being able to get into the OS to toggle OEM Unlock, I am kinda stuck and so far all my research has pointed me to the fact that this is impossible to do without doing it through Settings -> Developer Options, which I can't reach because I'm stuck in a boot loop.

Any ideas? Thanks in advance for any suggestions or help!

de0u

coolsnoo I think your next move is to contact the developers on the main Matrix channel: https://grapheneos.org/contact#community

Let us know what happens?

coolsnoo

de0u Thanks, I'll try that.

spl4tt

Normally it flashes the update to the other boot slot, so if that one is corrupt, you can still boot the old, working boot slot..
If one slot is corrupt, it should automatically switch back, but it seems that's not happening for you or you're heavily out of luck and it corrupted more than just the boot slot.

Try changing the slot via fastboot:

install android dev tools on your computer
boot phone with power+volume down until you see the fastboot screen
connect phone to computer, open terminal and type 'fastboot devices' to check if you see your device
change boot slot with 'fastboot --set-active a' or 'fastboot --set-active b'
then either 'fastboot reboot' or press the volume buttons on the phone to select 'start'

Either boot slot a or b is corrupt, I think fastboot shows you on what slot you are right now, so pick the other.

Good luck.

EDIT: Googling the boot slot switch command says it may be 'fastboot --set-active=a', so maybe that's correct :P

coolsnoo

spl4tt Thanks a lot for the suggestion and info! I'll try this and report back. I've been slacking anyway on contacting the devs (need to create a whole new account, etc...), so this seems like a path with less resistance. Fingers crossed.

coolsnoo

Ok I decided to not procrastinate and give it a go. Unfortunately, it seems the phone needs to be unlocked to execute the command, as I get the following error after doing fastboot --set-active=a: FAILED (remote: 'Fastboot command (set_active:) is not allowed when locked'). Same error with --set-active=b argument, as expected.

I normally appreciate how secure these devices are... except in this case!

Any other ideas? Or is contacting the devs looking like the only option for a chance at recovery here?

Thanks for all the help.

wooden11

Hi, I have exactly this problem. I can get into the fastboot mode, but i cannot get any further. Did you ever solve the problem? Or has anyone any advice on how to solve it?

Thanks