How to interrupt Android boot sequence to force it boot to Linux kernel only

Question

I am trying to do some low level performance testing related to device processor cores through adb which I feel it is affected by Android background services and system stuff.

As I know that the Android boot sequence stages are as follow:

1. Execute Boot ROM code.
2. Execute the boot loader.
3. Load the Linux kernel.
4. Launch Zygote, which initializes the Dalvik VM.
5. System server which loads the Android system.

So my question is how can I interrupt this sequence to force it stop on stage 3 to load Linux kernel. This can help me implement my intermediary performance testings before loading again Android system.

Does Fastboot or Clockworkmod recovery can help here and load my device to a kind of Linux kernel?

Any hint will be appreciated. Thanks.

Answer 1

No. Android's not like a desktop GNU/Linux distro, where you can press I to get an interactive boot, or skip X and just boot to a shell. The only way to achieve this would be to build your own custom ROM after editing the init scripts (which have much the same function as on a desktop GNU/Linux system) to tailor the boot process how you like.

Answer 2

If you are able to root your device or install alternative Android distro (Clockworkmod), you might have options available:

1. Rooting device: I am not sure if Android root image allows modification (read-write file system). If yes, you probably could edit the boot scripts to allow enabling your system modifications. Or moving the init process (not sure what that is in Android) away and replacing it with your own init program that after enabling your modifications would exec() the original init (init is the first process (with PID 1) that is run by unixy operating systems).
2. Using alternative Android distro (assuming CWN). If you can run CWN in your device, you could study how to build your own image and modify it for your needs.

Beyond the step of rooting or installing/running alternative image, gaining shell access, I have the impression that - once you determine which road to take - you could have better luck in getting the specifics (boot script locations and the way they operate, help with creating your own CWN image) answered at http://stackoverflow.com!