There are many books, articles and paper publications about Android and related applications but only a few are related to how Android operating system works internally.In this talk we will see how android boots up , an overview of zygote , how system server and package manager works. This talk will be extremely helpful to foster understanding among android developers about Android Internals as well as everybody else who desires a general understanding of the internal working of Android powered devices.

1. Android Internals
RAJESH KHETAN
Co-founder @ Bangalore Tech Events

2. Agenda
 Android Boot Up Process
 How Package Manager Service works ?

3. A Typical Android Boot-Up
KERNEL
Installd,
adbd,
servicemanger...
System Server
Zygote
App 1 , App 2 …App N
INIT

4. A Typical Android Boot-Up
KERNEL
Installd,
adbd,
servicemanger...
System Server
Zygote
App 1 , App 2 …App N
INIT

5. Kernel
 Special forked version of Linux
 Features :
 Wake locks
 Low Memory Killer (OOM adjustment)
 Provides Binder driver

6. A Typical Android Boot-Up
KERNEL
Installd,
adbd,
servicemanger...
System Server
Zygote
App 1 , App 2 …App N
INIT

7. INIT
 Root / First User Space process
 Responsibilities :
 Set up file system permissions
 Start native daemons

8. A Typical Android Boot-Up
KERNEL
Installd,
adbd,
servicemanger...
System Server
Zygote
App 1 , App 2 …App N
INIT

9. A Typical Android Boot-Up
KERNEL
Installd,
adbd,
servicemanger...
System Server
Zygote
App 1 , App 2 …App N
INIT

10. Zygote
 Base of all other java processes
 The app_process command invokes Android Runtime to start the first DVM/ART
 The VM then invokes zygotes main method (ZygoteInit.java)

11. Zygote
Register Zygote Socket
fork systemserver
Preloads Classes And Resources
Wait for requests
fork()

12. Zygote
Register Zygote Socket
fork systemserver
Preloads Classes And Resources
Wait for requests
fork()

13. Zygote
Register Zygote Socket
fork systemserver
Preloads Classes And Resources
Wait for requests
fork()

14. Zygote
Register Zygote Socket
fork systemserver
Preloads Classes And Resources
Wait for requests
fork()

15. Zygote
Register Zygote Socket
fork systemserver
Preloads Classes And Resources
Wait for requests
fork()

16. A Typical Android Boot-Up
KERNEL
Installd,
adbd,
servicemanger...
System Server
Zygote
App 1 , App 2 …App N
INIT

17. A Typical Android Boot-Up
KERNEL
Installd,
adbd,
servicemanger...
System Server
Zygote
App 1 , App 2 …App N
INIT

18. System Server
 Heart of the Android System
 Start system services
 Register services with the service manager

19. System Server
Creates system context
Start bootstrap services
Start Other Services
Start core services
ActivityManagerService
PackageManagerService
WindowManagerService
Wifi/Bluetooth Service
SystemUI
Loads server library

20. System Server
Creates system context
Start bootstrap services
Start Other Services
Start core services
ActivityManagerService
PackageManagerService
WindowManagerService
Wifi/Bluetooth Service
SystemUI
Loads server library

21. System Server
Creates system context
Start bootstrap services
Start Other Services
Start core services
ActivityManagerService
PackageManagerService
WindowManagerService
Wifi/Bluetooth Service
SystemUI
Loads server library

22. System Server
Creates system context
Start bootstrap services
Start Other Services
Start core services
ActivityManagerService
PackageManagerService
WindowManagerService
Wifi/Bluetooth Service
SystemUI
Loads server library

23. System Server
Creates system context
Start bootstrap services
Start Other Services
Start core services
ActivityManagerService
PackageManagerService
WindowManagerService
Wifi/Bluetooth Service
SystemUI
Loads server library

24. System Server
Creates system context
Start bootstrap services
Start Other Services
Start core services
ActivityManagerService
PackageManagerService
WindowManagerService
Wifi/Bluetooth Service
SystemUI
Loads server library

25. System Server
Creates system context
Start bootstrap services
Start Other Services
Start core services
ActivityManagerService
PackageManagerService
WindowManagerService
Wifi/Bluetooth Service
SystemUI
Loads server library

26. System Server
Creates system context
Start bootstrap services
Start Other Services
Start core services
ActivityManagerService
PackageManagerService
WindowManagerService
Wifi/Bluetooth Service
SystemUI
Loads server library

27. System Server
Creates system context
Start bootstrap services
Start Other Services
Start core services
ActivityManagerService
PackageManagerService
WindowManagerService
Wifi/Bluetooth Service
SystemUI
Loads server library

28. Package Manager Service
 Responsibilties :
 Installation/Uninstallation of apps
 Managing Permissions & Certificate Handling
 Exposing APIs to 3rd party applications

29. Package Manager Service(Flow)
Scan Packages
Grant Permissions
Initialization
Manifest Parsing
Perform DexOpt
Collect Certificates
Generate Package Info
Asset Loading

30. Package Manager Service(Flow)
Scan Packages
Grant Permissions
Initialization
Manifest Parsing
Perform DexOpt
Collect Certificates
Generate Package Info
Asset Loading

31. Package Manager Service(Flow)
Scan Packages
Grant Permissions
Initialization
Manifest Parsing
Perform DexOpt
Collect Certificates
Generate Package Info
Asset Loading

32. Package Manager Service(Flow)
Scan Packages
Grant Permissions
Initialization
Manifest Parsing
Perform DexOpt
Collect Certificates
Generate Package Info
Asset Loading

33. Package Manager Service(Flow)
Scan Packages
Grant Permissions
Initialization
Manifest Parsing
Perform DexOpt
Collect Certificates
Generate Package Info
Asset Loading

34. Package Manager Service(Flow)
Scan Packages
Grant Permissions
Initialization
Manifest Parsing
Perform DexOpt
Collect Certificates
Generate Package Info
Asset Loading

35. Package Manager Service(Flow)
Scan Packages
Grant Permissions
Initialization
Manifest Parsing
Perform DexOpt
Collect Certificates
Generate Package Info
Asset Loading

36. Package Manager Service(Flow)
Scan Packages
Grant Permissions
Initialization
Manifest Parsing
Perform DexOpt
Collect Certificates
Generate Package Info
Asset Loading

37. Package Manager Service(Flow)
Scan Packages
Grant Permissions
Initialization
Manifest Parsing
Perform DexOpt
Collect Certificates
Generate Package Info
Asset Loading

38. Package Manager Service
 Package information is cached into /data/system/packages.xml
 Runtime permissions are cached into /data/system/0/runtime_packages.xml

39. PackageIntsaller
Offers the ability to install, upgrade, and
remove applications on the device.

40. PackageInstallerActivity
 Launched when a new application is installed via side loading
 Display parsing errors via a dialog.
 Enable unknown applications setting.
 Memory check
 Check for same existing package
 Install app

41. Installd
 PMS lacks root privileges
 Creating , deleting & changing the ownership of applications directories requires superuser capabilities .
 The PMS delegates these operations to the installd daemon

42. A Quick Recap
Native Daemons
Zygote
Launcher
System Server
Activity Manager
Android Runtime
Kernel Init

43. A Quick Recap
Native Daemons
Zygote
Launcher
System Server
Activity Manager
Android Runtime
Kernel
- Initialization
- Mount root FS
- Starts Init Process
Init

44. A Quick Recap
Native Daemons
Zygote
Launcher
System Server
Activity Manager
Android Runtime
Kernel
Init
- Set up env variables
- Mount FS
- Set UP FS perm
- Start native daemons

45. A Quick Recap
Native Daemons
- servicemanager
- app_process -X Zygote
- adbd
- installd
Zygote
Launcher
System Server
Activity Manager
Android Runtime
Kernel Init

46. A Quick Recap
Native Daemons
Zygote
Launcher
System Server
Activity Manager
Android Runtime
- Start first VM
- Call zygote’s main method
Kernel Init

47. A Quick Recap
Native Daemons
Zygote
- Register Zygote socket
- Preload classes & res.
- Start systemserver process
- Listen for connections
Launcher
System Server
Activity Manager
Android Runtime
Kernel Init

48. A Quick Recap
Native Daemons
Zygote
Launcher
System Server
- Start services
- Register with service manager
Activity Manager
Android Runtime
Kernel Init

49. A Quick Recap
Native Daemons
Zygote
Launcher
System Server
Activity Manager
- Init itself
- Send Intent.Category_HOME
- Send BOOT_COMPLETE
Android Runtime
Kernel Init

50. A Quick Recap
Native Daemons
Zygote
Launcher
- Init itself
- Register OnClick handlers
System Server
Activity Manager
Android Runtime
Kernel Init

51. A Quick Recap
Native Daemons
Zygote
Launcher
System Server
Activity Manager
Android Runtime
Kernel Init
Click

52. A Quick Recap
Native Daemons
Zygote
Launcher
System Server
Activity Manager
Android Runtime
Kernel Init
Click

53. A Quick Recap
Native Daemons
Zygote
Launcher
System Server
Activity Manager
Android Runtime
Kernel Init
Click

54. A Quick Recap
Native Daemons
Zygote
Launcher
System Server
Activity Manager
Android Runtime
Kernel Init
Click

55. A Quick Recap
Native Daemons
- servicemanager
- app_process -X Zygote
- adbd
- installd
Zygote
- Register Zygote socket
- Preload classes & resources
- Start systemserver process
- Listen for connections
Launcher
- Init itself
- Register OnClick handlers
Click
System Server
- Start services
- Register with servicemanager
Activity Manager
- Init itself
- Send Intent.Category_HOME
- Send BOOT_COMPLETE
broadcast
New app
Android Runtime
- Start first VM
- Call zygote’s main method
Kernel
- Initialization
- Mount root FS
- Starts Init Process
Init
- Set up env variables
- Mount FS
- Set UP FS perm
- Start native daemons

56. THANK YOU
 References :
 Embedded Android – Karim Yaghmour
 https://android.googlesource.com/
www.bangaloretechevents.com
rajeshkhetan.rk@gmail.com
Contact :