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SubjectRe: Possible bug in wait4(), 2.1.126-129 ?
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Ion Badulescu writes ("Re: Possible bug in wait4(), 2.1.126-129 ?"):
>
> 4. the program *must* be run from cron, doesn't matter which user.
>[snip]
>
> wait4: No child processes

The different behaviour comes from cron, not the kernel.
Have a look at /proc/self/status for a process run from cron.
On a libc5, 2.0.35 system running vixie-cron 3.0.1, I found:
SigIgn: 80000000
On a libc6, 2.1.125 system running vixie-cron 3.0.1, I found:
SigIgn: 0000000000010000
^
Ignoring SIGCHLD causes automatic child reaping.
The difference comes from vixie-cron-3.0.1/do_command.c:

#ifdef USE_SIGCHLD
/* our parent is watching for our death by catching SIGCHLD. we
* do not care to watch for our children's deaths this way -- we
* use wait() explictly. so we have to disable the signal (which
* was inherited from the parent).
*/
(void) signal(SIGCHLD, SIG_IGN);
#else
/* on system-V systems, we are ignoring SIGCLD. we have to stop
* ignoring it now or the wait() in cron_pclose() won't work.
* because of this, we have to wait() for our children here, as well.
*/
(void) signal(SIGCLD, SIG_DFL);
#endif /*BSD*/
I suspect the difference is in the way that the configure script
interacted with the libc. In the USE_SIGCHLD case, you need
signal(SIGCLD, SIG_DFL) below the vfork to reset the signal handling
for the grandchild process.

Peter

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