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signalsforkparent-childkillsigchld

SIGCHLD sended by another process to parent

Let's assume that our process creates a child and then calls wait().

When I try to send signal() or do 

kill -SIGCHLD <PID>

nothing happens at all.

So the question is: How does the process in Linux determine that signal SIGCHLD hadn't been sent by the child? Or, maybe, there is some another mechanism?

Solution

  • The kernel takes care of this.

    wait() is not a signal handler listening for (any) SIGCHLD sent to a process, as it might be established via sigaction() or signal().

    From wait()'s POSIX spec (emphasis by me):

    The wait() and waitpid() functions shall obtain status information pertaining to one of the caller's child processes.