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    SubjectRE: Possible bug in wait4(), 2.1.126-129 ?
    On Sun, 22 Nov 1998, Greaves Tristan TM wrote:

    > [cut lots of stuff]
    >
    > I missed the original posting here - could someone please tell me what
    > the actual symptons are, as I suspect I know what may be causing the
    > problem.

    Basically, a perl script running another command using the backticks
    syntax (`foo`), from cron (this is important for some reason), ends up
    receiving ECHILD for the child's exit status.

    Simplest test case:

    #!/usr/bin/perl
    `cmp -s /bin/ls /bin/ls`;
    die "$!" if ($? != 0);

    If I run this from cron (as root, haven't tried it yet as myself), I get a
    mail saying:

    No child processes at <script filename> line 3.

    In terms of system calls, it goes like this:

    pipe()
    fork()
    [parent pid] read from pipe(...
    [child pid] do something
    [child pid] exit(0)
    [parent pid] read from pipe() resumed
    wait4(child pid) = -ECHILD

    I can reproduce this at will. Yet, it's a "theoretically impossible"
    situation.


    Ion

    --
    It is better to keep your mouth shut and be thought a fool,
    than to open it and remove all doubt.



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