How Android works

Boot

From a press of the power button to a home screen, step by step.

4 pages58 min4 interactive9000 words

01The boot sequenceFrom a press of the power button to the first frame of the home screen: eight stages, four signed handoffs, and a device that has to prove what it is running before it is allowed to run it.intermediate14 mininteractive
02init and init.rcOne small C++ program is PID 1, mounts the world, loads the security policy, starts every daemon and restarts them when they die. Its configuration language is the closest thing Android has to an init system.nerd14 mininteractive
03Verified boot and A/B updatesTwo mechanisms that make an Android phone trustworthy and hard to brick: a chain of signatures rooted in hardware, and two copies of the system so an update can never destroy the one you are using.nerd15 mininteractive
04Partitions and why there are so manyA modern Android device has around twenty partitions, and the list keeps changing. Each one exists because some part of the system needed to be updated, verified or mounted independently of the rest.intermediate15 mininteractive

Test yourself

Test yourself: Boot

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Which values can androidboot.verifiedbootstate report? Select all that apply.