Zombie processes

user_291962 0
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I'v some questions about zombie processes

  • what the benefits from zombie process concept?
  • know that the kernel keeps (PID,termination status, resource usage information) for zombie process
    what's the meaning of "resource usage information"
  • how zombie's PPID() = 1 and it still zombie , (init reaps Zombies because it wait() by default)
    can any one write some C code to make a zombie it's parent is Init?
  • can zombies refusing to release some lock on memory??

thanks in advance

systems-programming posix process unix c
4 Answers

Zombie processes are processes that have stopped running but their process table entry still exists because the parent process hasn't retrieved it via the wait syscall. Technically each process that terminates is a zombie for a very short period of time but they could live for longer.

Longer lived zombie processes occur when parent processes don't call the wait syscall after the child process has finished. One situation where this occurs is when the parent process is poorly written and simply omits the wait call or when the parent process dies before the child and the new parent process does not call wait on it. When a process' parent dies before the child, the OS assigns the child process to the "init" process or PID 1. i.e. The init process "adopts" the child process and becomes its parent. This means that now when the child process exits the new parent (init) must call waitto get its exit code or its process table entry remains forever and it becomes a zombie

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