““Learning AOSP”Learning AOSP”
Android Booting ProcessAndroid Booting Process
Nanik TolaramNanik Tolaram
@nanikjava@nanikjava
ozandroid.infoozandroid.info

Thank You !Thank You !

ArchitectureArchitecture

Questions !Questions !
 What happened when I press power on button in my AndroidWhat happened when I press power on button in my Android
device ?device ?
 What is Android boot sequence ?What is Android boot sequence ?
 What is bootloader ?What is bootloader ?
 What is Zygote ?What is Zygote ?
 What is init.rc ?What is init.rc ?
 What is System Server ?What is System Server ?

Boot Execution PathBoot Execution Path
Boot ROM
Boot Loader
Kernel
Init
Zygote
System Servers
hardware
boot.img, C & ASM, rootfs
system.img,
Android framework & apps
u-boot or different fork

Boot ROM & BootBoot ROM & Boot
LoaderLoader
Power ON
On chip ROM (during
CPU production)
Primary Boot
Loader
Secondary
Boot Loader
Hardware Init
Modem Image
Execution
Kernel Image
Download & Execution
1st
loaded from flash
(normally)/fastboot

KernelKernel
 Nothing Special !Nothing Special !
 Standard Linux Kernel ExecutionStandard Linux Kernel Execution
 Hardware & Android Device DriversHardware & Android Device Drivers
 Needed in recovery and system partitionNeeded in recovery and system partition

InitInit
 Main entry point to AndroidMain entry point to Android
 init.rc and other .rc configinit.rc and other .rc config
 Initialisation and preparationInitialisation and preparation
 Android framework initialisationAndroid framework initialisation
 Environment properties setupEnvironment properties setup
 Security setupSecurity setup
 Mounting of different media partitionsMounting of different media partitions
 System servers initialisationSystem servers initialisation

ZygoteZygote
 Initialise duringInitialise during InitInit processprocess
 service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-
serverserver
 Registers server socketRegisters server socket
 Preload Java classes from “preloaded-Preload Java classes from “preloaded-
classes” fileclasses” file
 Preload native themes and layoutsPreload native themes and layouts

System ServersSystem Servers
 System Servers written both as Native &System Servers written both as Native &
JavaJava
 startSystemServer() methodstartSystemServer() method
 Power Manager, Zygote, ActivityPower Manager, Zygote, Activity
Manager, Telephony Registry, BatteryManager, Telephony Registry, Battery
Service and many moreService and many more

Boot CompleteBoot Complete
 ACTION_BOOT_COMPLETEDACTION_BOOT_COMPLETED
broadcast Intent will firebroadcast Intent will fire

Boot SequenceBoot Sequence
DecisionDecision
Bootloader Microcode
Boot Partition
System Partition Recovery Partition
Recovery
Y
N
Execute Recovery AppRun Android Stack
Bootloader (1st, 2nd, nth)

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