The document discusses Process Control Daemon (PCD), an open source process manager for embedded Linux platforms. PCD aims to improve over traditional shell script-based startup by allowing deterministic, parallel startup and recovery actions for processes. It provides a centralized way to define and manage processes and their dependencies. Key features include event-driven startup, crash handling and logging, and a process API. PCD has modest resource needs and supports various architectures. It has benefited products by improving startup time, robustness, and debug capabilities.

1. Process Control DaemonFor Embedded Linux PlatformsSpeaker: Hai Shalomrt-embedded.com/pcd

2. Background review: What were the reasons that led to the development of PCD.PCD project review: Features and high level overview of the project.Live demonstration.Q & A.Agenda

3. Does your product have a process controller?Does your product automatically recover after a crash?Do you think your product’s boot time is fast enough?Are you using methods other than printf to debug a crashed application?Are you familiar with all the processes which are running in your product and their dependencies?Some questions

4. Most of you probably answered “No” to at least one question.People who answered “Yes” to all questions are probably using PCD already!Let’s review some facts about Embedded Linux based products…What were your answers?

5. Done by scripts (rcS, rc.*). These are great, but might be:Not optimal for embedded / not deterministic:

6. Limited ways to synchronize depended processes(delay).

7. Limited ways to verify successful start of a process

8. No error checking (usually).

9. No formal way to define dependencies.

10. Difficult to start processes in parallel.

11. Not trivial to understand, maintain and extend:

12. Require additional shell scripting expertise.

13. Tend to be long and unreadable.

14. Plenty of commented code, old remarks, different code styles.System start up

15. Done by scripts (rcS, rc.*). These are great, but might be:Not optimal for embedded / not deterministic:

16. Limited ways to synchronize depended processes (delay).

17. Limited ways to verify successful start of a process

18. No error checking (usually).

19. No formal way to define dependencies.

20. Difficult to start processes in parallel.

21. Not trivial to understand, maintain and extend:

22. Require additional shell scripting expertise.

23. Tend to be long and unreadable.

24. Plenty of commented code, old remarks, different code styles.System start upLooks familiar?

25. A crashed program just terminates, usually after printing “Segmentation Fault”.Now what?

26. Where is the debug information?

27. Kernel crashes are assumed to be handled by the system’s watchdog.Signal Handlers not always implemented correctly.Unsafe to use printf, and many other functions.The system remains unstable and unusable. End user must power-cycle (again?).Crash handling and recovery

28. A crashed program just terminates, usually after printing “Segmentation Fault”.Now what?

29. Where is the debug information?

30. Kernel crashes are assumed to be handled by the system’s watchdog.Signal Handlers not always implemented correctly.Unsafe to use printf, and many other functions.The system remains unstable and unusable. End user must power-cycle (again?).Crash handling and recovery

31. No central management entity.init is the parent of all processes.Must know process’ pid in order to signal or kill.Each process must manage his own children.Child process inherits his father’s priority.

32. Parents must retrieve child’sexit status, or else we end upwith Zombies…Process management

33. A customer reports a crash in the field or in his lab tests:There is no standard method for generating and collecting remote debug information.

34. When a process abnormally terminates, all its information goes away and no log is saved.

35. You might be on the next flight to the customer’s lab.Field/Remote debugging

36. A great (and free) solution: PCDWhat is PCD?

37. What is PCD?PCD – Process Control Daemon, is an open source, light-weight system level process manager for Embedded-Linux based products (consumer electronics, network devices, etc).The PCD provides a complementary service for any Embedded Linux driven product. Designed and implemented by Hai Shalom during employment at Texas Instruments for Next-Gen Puma5 Cable chipset.Released to open source as part of his M.Sc. Degree research.PCD is a proven solution that already drives millions of devices in the world.

38. System startup: PCD starts up the system in an efficient, synchronized and deterministic manner.Process management: a centralized entity that controls and monitors all processes, and provides API to manage them. System recovery: Configurable per process recovery action is taken in case of a crash.Debug information: PCD provides a detailed crash log in case of a program error.PCD Features in high-level

39. How does it work?What are the advantages of products with PCD?

40. Rule blocks replace/extend traditional shell scripts.Each rule defines a single process.Rule inter-dependency is well defined.PCD Scripts: Rule blocksProcess 1Rule 1PCDScriptFileProcess 2Rule 2Process 3Rule 3

41. Very simple and readable syntax.Easy to extend and maintain.Each Rule block is based on the same template and contains the following details:What is the process name and parameters?

42. When to start it (depends on event…)?

43. What is the required priority?

44. What is the completion event?

45. How much time to wait for it to complete?

46. What to do in case of a crash?PCD Scripts: Rule blocks

47. Very simple and readable syntax.Easy to extend and maintain.Each Rule block is based on the same template and contains the following details:What is the process name and parameters?

48. When to start it (depends on event…)?

49. What is the required priority?