> For the complete documentation index, see [llms.txt](https://notes.tejpratapsingh.com/_/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://notes.tejpratapsingh.com/_/android-tips/interview/aosp.md). # AOSP ### Boot 1. Walk through the complete Android boot sequence from power-on to `system_server` startup. 2. What is the role of the Boot ROM, and how does it verify the next stage bootloader? 3. Explain the differences between U-Boot, Little Kernel (LK), and proprietary bootloaders in AOSP. 4. How does `avb_verify` work in the context of Verified Boot 2.0 (AVB)? 5. What is the purpose of the `boot.img` header, and how do the V3 and V4 formats differ from V1/V2? 6. Describe the process of loading and verifying the `vendor_boot` partition. 7. How does the bootloader pass the kernel command line and device tree (DTB) to the Linux kernel? 8. What is the role of `init` in early userspace, and how does it parse `init.rc` scripts? 9. Explain the difference between early-init, init, and late-init stages in `init.rc`. 10. How does `init` handle the transition from the rootfs ramdisk to the system partition? 11. What is the purpose of the `system/etc/init/` directory and how does it relate to first-stage vs second-stage `init`? 12. How do you debug early boot failures before `logd` and `logcat` are available? 13. Explain how dm-verity is initialized during boot and its impact on I/O performance. 14. What is the purpose of the `vbmeta` partition, and how are rollback indexes used? 15. How does the boot sequence differ between a normal boot and a recovery boot? *** ### Build 1. Explain the AOSP build system architecture: how do `Soong`, `Kati`, and `Ninja` interact? 2. What is the difference between `Android.bp` and `Android.mk`, and when would you still need the latter? 3. How does the `Android.bp` module system handle dependencies between shared libraries and static libraries? 4. Describe the purpose of `AndroidProducts.mk`, `BoardConfig.mk`, and `device.mk` in a device build. 5. How do you add a new HAL implementation to the build without modifying AOSP core repositories? 6. Explain the difference between `eng`, `user`, `userdebug`, and `user` build variants at the build system level. 7. What is the purpose of `sepolicies` in the build, and how are they compiled into the final image? 8. How does the build system generate OTA packages, and what is the role of `releasetools.py`? 9. Describe how to create a custom build target that packages additional prebuilt binaries. 10. What are `apex` modules, and how do they change the traditional system image partitioning? 11. How does the build system handle kernel compilation out-of-tree vs in-tree? 12. Explain the purpose of `PRODUCT_COPY_FILES` vs `PRODUCT_PACKAGES` and their build-time implications. 13. How do you implement a build-time flag that conditionally compiles source code across multiple modules? 14. What is the role of `bionic` in the build, and how does it differ from glibc-based builds? 15. How would you optimize a clean AOSP build time for a large team using distributed build caches? *** ### Framework 1. Explain the Zygote startup process and why it uses a prefork model. 2. What happens during `ZygoteInit` before the first application process is forked? 3. Describe the Binder IPC mechanism: how does a client obtain a reference to a system service? 4. What is the difference between `BpBinder` and `BBinder`, and how does the proxy/stub pattern work in native code? 5. How does `AIDL` differ from `HIDL` and `AIDL` (stable) in terms of interface stability and versioning? 6. Explain the role of `ServiceManager` vs `hwservicemanager` vs `vndservicemanager`. 7. What is the purpose of the `system_server` process, and how is it started from Zygote? 8. Describe the `ActivityThread` initialization sequence when an application process starts. 9. How does the `PackageManagerService` scan and resolve packages during boot? 10. Explain the difference between `system` permissions, `signature` permissions, and `normal` permissions in `AndroidManifest.xml`. 11. How does the `WindowManagerService` manage window layers and surface composition? 12. Describe the input event pipeline from kernel to application: `EventHub`, `InputManagerService`, `InputDispatcher`. 13. What is the role of `SurfaceFlinger` in the display pipeline, and how does it interact with HWC? 14. How does the `PowerManagerService` coordinate with the kernel for suspend/resume and wakelocks? 15. Explain the `JobScheduler` framework and how it interacts with Doze mode and App Standby. 16. What is the difference between a `ContentProvider` running in its own process vs the caller's process? 17. How does the `ActivityManagerService` handle process lifecycle and out-of-memory killing decisions? 18. Describe how `BroadcastReceiver` delivery works, including ordered vs unordered broadcasts and background restrictions. 19. What is the purpose of `Looper`, `Handler`, and `MessageQueue` in the Android threading model? 20. How does the `Resources` framework handle runtime resource overlay (RRO) and static overlay? *** ### System Service 1. How do you implement a new system service that is accessible to third-party applications? 2. What is the difference between a Java system service and a native system service in terms of registration? 3. Explain the `SystemService` base class and the `onStart()`, `onBootPhase()`, and `onUserStarting()` lifecycle methods. 4. How do you ensure thread safety in a system service that receives concurrent Binder calls? 5. Describe the watchdog mechanism (`Watchdog.java`) and how to register a system service with it. 6. How does `ActivityManagerService` enforce background execution limits introduced in recent Android versions? 7. Explain the architecture of `ConnectivityService` and how it manages multiple network agents. 8. How does `LocationManagerService` interact with GNSS HAL and fuse location providers? 9. Describe the power management flow from `PowerManagerService` to the kernel power HAL. 10. How does `BatteryService` monitor battery state and propagate events to the framework? 11. Explain the role of `StorageManagerService` and how it handles adopted storage vs portable storage. 12. How does `AudioService` manage audio focus, routing, and policy decisions across HAL implementations? 13. Describe the `CameraService` architecture and how it handles concurrent camera access from multiple apps. 14. What is the purpose of `SensorService`, and how does it batch sensor events for power efficiency? 15. How does `TelephonyRegistry` dispatch phone state changes to multiple listeners securely? 16. Explain the `VibratorService` and `LightsService` abstractions over their respective HALs. 17. How would you add a custom hardware feature (e.g., a proprietary sensor) and expose it through the framework? 18. Describe how `DevicePolicyManagerService` enforces enterprise policies at the system service level. 19. How does `NetworkManagementService` use `netd` to configure iptables and routing rules? 20. What is the role of `AppOpsService` and how does it provide fine-grained permission auditing beyond runtime permissions? --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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