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    Subject2.6.x Fork Problem?
    All,
    We've got an application (we'll call it AppB) based on apache and a
    proprietary module that we push to other Linux boxes. The way we do this is
    first push a proprietary executable (we'll call it AppA) to the Linux box
    via rexec or some other mechanism. We then send messages to AppA and tell
    it to pull AppB from some place. AppA will pull AppB and run its installer,
    and then starts AppB via a shell script. So process wise, we have a tree
    like this:

    init
    |
    |-AppA
    |
    |-AppB

    Once AppB is running, the apache module will periodically call fork and one
    of the execs to execute some other process. AppB will execute code like
    this to fork the process:

    pid = fork();
    switch (pid)
    {
    case -1:
    blah; /* big trouble */
    break;
    case 0: /* Child */
    blah;
    blah;
    exec(some command here)
    blah; /* If we get here, we're in big trouble. */
    break;
    default: /* Parent */
    pid2 = waitpid(pid, &status, 0);
    if (pid2 == -1)
    {
    blah; /* check out errno */
    }
    }

    On 2.4.x, this code works great. But now with 2.6.x (stock SuSE 9.1 and FC2
    kernels, as well as home grown kernels), waitpid will always return -1, and
    errno will be 10 (ECHILD, No child processes). We know for a fact that the
    fork and exec calls succeed due to debug print outs. Here's the real
    kicker. We only see this problem when we first push the software and start
    it. If we push the software and start it, stop it and start it again, then
    allow it to try the fork/exec again, it succeeds. We have the same problem
    if we bundle the entire application (AppA and AppB) into an installer and
    use that to install it on a machine. The installer will start the
    application, and the fork/exec calls will fail with ECHILD. If we then stop
    the App and start it again, everything is fine.

    I've widdled the code down to just do this:

    pid = fork();
    switch (pid)
    {
    case -1:
    blah; /* big trouble */
    break;
    case 0: /* Child */
    exit(1);
    break;
    default: /* Parent */
    pid2 = waitpid(pid, &status, 0);
    if (pid2 == -1)
    {
    blah; /* check out errno */
    }
    }

    and I get the same results, so I now the exec has nothing to do with it.

    Anyone have any ideas on why this would happen?

    Thanks,

    Torin Ford
    Venturi Technology Partners


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