Tools

Get into recovery

Force a restart by holding Power, then use your phone's key combo, usually Power with a volume key. If it offers to wipe the cache, try that first. It leaves your files alone.

Try the other slot

Newer phones keep two copies of the system. With an unlocked bootloader, you can boot the other one from fastboot.

fastboot getvar current-slot
fastboot --set-active=b

Use whichever of a or b isn't current.

Reflash the software you were on

Use the same build if you can. Unlocked phones can flash images from fastboot. Locked phones can only sideload a signed update from stock recovery.

adb sideload <update>.zip

Factory reset as the last step

This fixes most bootloops caused by bad data, but it erases your files. Read saving your files first.

Get firmware for your exact model and region

Phones sold under one name can have several models, and firmware often isn't interchangeable between them.

Flash it the way its maker intended

Follow the instructions that come with the firmware. Some packages include a flash script, others are an update you sideload from recovery. Expect your data to be erased.

Boot it before you touch anything else

Finish setup and check that calls, Wi-Fi and updates work.

Relock only if you need to

Only relock once the phone is running completely unmodified stock software. Locking on anything else can leave it unable to boot. Relocking also erases your data.

fastboot flashing lock

Find the images

Look in the downloads below first. Otherwise, many full firmware zips hold everything in a payload.bin, which a payload dumper can unpack into separate images.

Flash boot-level images from the bootloader

Images like boot, init_boot, vendor_boot and dtbo go here. Your bootloader needs to be unlocked.

fastboot flash boot boot.img

Flash system partitions from fastbootd

On phones with dynamic partitions, system, vendor and product live in a separate userspace fastboot.

fastboot reboot fastboot
fastboot flash system system.img

Keep images from the same build

Mixing images from different builds is a common cause of bootloops. A Generic System Image is the exception: it's built to run on other devices' vendor images, so check your Android version and architecture.

Rule out the simple causes

Charge it for 30 minutes with a known good cable, then hold Power for at least 30 seconds. A fully drained phone can look dead.

See what your computer finds

Plug it in and check for a new USB device. On Qualcomm phones, emergency download mode shows up as QDLoader 9008, or 05c6:9008 in lsusb. MediaTek phones have a similar low-level mode called BROM.

Use a package made for your exact model

A low-level flash can rewrite everything, so the package has to match. Many phones also only accept signed or authorised files, so a matching package may still be refused.

Know when to stop

If your computer sees nothing at all, the problem may be hardware. A repair shop or the maker is the next step.

Try a normal boot first

Even a phone that crashes after a minute may give you time to sync photos, or turn on a backup.

Try ADB

This works if the phone boots far enough and already trusts your computer, or from a custom recovery that can read your data.

adb devices
adb pull /sdcard/DCIM

Accept what can't be reached

Android encrypts your data, and flashing tools can't read it without your phone unlocking it. Avoid paid "recovery" tools that promise otherwise. Anything not backed up may be gone once you wipe.

Install platform-tools

Google's platform-tools include adb and fastboot. Get them from the flash tools below, and add a USB driver if you're on Windows.

Check your phone connects

Turn on USB debugging in Developer options, accept the prompt on the phone, then restart to the bootloader.

adb devices
adb reboot bootloader
fastboot devices

Unlock the bootloader, if your phone allows it

Enable OEM unlocking in Developer options first. Unlocking erases your data, and some makers require their own unlock step or don't allow it at all.

fastboot flashing unlock