sqall's blog

For a project I am currently working on I needed an old mobile phone with Android (a Motorola Moto G 2014) to automatically boot up as soon as it gets charged. In this project, the mobile phone is always connected to a charger and as soon as this charger gets power, the phone should start its boot process. Normally, any mobile phone goes into a special "charging screen". I searched a lot in the depth of the Internet but did not find much about this topic. Therefore, I write this article so others do not have the same problem (and I have notes available if I want to do it again ). Since this is a change to the operating system, I needed something like LineageOS to have access to it. So, this is a description how to set up your LineageOS 16 to boot up as soon as it gets power via the charger. However, I also tested it on LineageOS 15.1 on a Nexus 5X and it works.


Installing LineageOS 16

The first step is to install LineageOS 16 onto your mobile phone. I will not describe how this is done, because the LineageOS website has really good tutorials for this (here for the Moto G 2014). Since my phone is no longer supported, there are no official images for it. But I did not want to build LineageOS for myself. So I searched for unofficial builds and found one with the name lineage-16.0-20190420-UNOFFICIAL-titan.zip. I used this to flash my mobile phone. Additionally, please install the LineageOS SU Addon to get root permissions on the phone. When everything is working, we can start our changes to the operating system.


Auto Boot on Charging

As I said, I tested a lot of different methods I found on the Internet. The one that worked for me I found in a forum thread. In a short description, we have to change the init.rc in the boot image. However, for this we have to reflash the mobile phone. I tried to change the file directly via adb (getting write permissions to the file and editing it directly). However, after each reboot it changes back to the original file. So, we have to change it in the boot image itself.

Normally, I work on Linux. However, since there is a Windows tool that does all the packing and repacking (and I actually do not care about the Android image internals), I used Windows for this part. The steps we have to do are the following:

1. Download Android Image Kitchen. I used version 3.5.


2. Unzip our LineageOS file (the lineage-16.0-20190420-UNOFFICIAL-titan.zip) and copy the boot.img into the Android Image Kitchen directory (next to unpackimg.bat and repackimg.bat).


3. Open a command line in Windows into this directory and execute:




unpackimg.bat boot.img
 



4. Go into the directory ramdisk and edit the file init.rc. I would suggest to use Notepad++ for this, since the normal Windows editor could fuck up the charset (e.g., by using \r\n instead of \n).


5. Find the section that starts with on charger and change it to the following:




#[...]
on charger
    class_start charger
    class_stop charger
    trigger late-init
#[...]
 



6. Repack the image by open a command line into the Android Image Kitchen directory and execute repackimg.bat. You should now have a file that is called image-new.img. This is our new boot image.


7. Copy the image-new.img to your phone (I used a SD card for this).


8. Start TWRP on your phone (you used it to flash your LineageOS onto your phone, so do the same steps to go into the recovery mode which uses TWRP).


9. In TWRP, go to install, switch to install image and then select the image-new.img file you copied to your phone. Select the boot partition and swipe to install it. In short, do install -> install image -> select image-new.img -> select boot partition -> swipe to install.


10. Reboot.


11. Done.

After this, the mobile phone should boot up as soon as your charger delivers power to it. If you want to check if your changes are now on the phone, you can use adb for it. Do the following if you want to check:

1. Turn on the developer options on your mobile phone.


2. Allow USB debugging.


3. Allow adb to have root access.


4. Use the command adb root on your computer to restart adb with root access.


5. Use the command adb shell to get a shell on the phone.


6. Output the file init.rc file via cat init.rc and see if your changes are there.

So, I hope this is useful for others that have the same problem as I did.