[launchd-dev] Preventing killing of child processes?

[Dave Keck]

> That doesn't seem to be doing it. The child process still exits as
> soon as it unloads the parent job from launchd.

Hmm, I just did a controlled test, and it certainly does the trick for
me on 10.5.8. Here's what I did:

===== parent_process.c

#include <stdio.h>
#include <unistd.h>

int main(int argc, const char *argv[])
{
    if (!fork())
    {
        execl("/child_process", "/child_process");
        _exit(0);
    }
    sleep(10);
    return 0;
}

===== child_process.c

#include <stdio.h>
#include <unistd.h>

int main(int argc, const char *argv[])
{
    setpgrp();
    sleep(60);
    return 0;
}

===== com.parent.parent_process.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
"http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Label</key>
<string>com.parent.parent_process</string>
<key>ProgramArguments</key>
<array>
<string>/parent_process</string>
</array>
<key>RunAtLoad</key>
<true/>
</dict>
</plist>

=====

Compile parent_process.c and child_process.c, and put them and the
plist in your drive's root directory. Then:

    launchctl load /com.parent.parent_process.plist

You'll notice that the parent exits after 10 seconds, while the child
stays alive for a full minute. Likewise, if you unload the parent
early, the child still stays alive past the parent's death. Without
setpgrp(), the child dies with the parent. Does that help?