SIGCHLD may be inherited blocked

[Nicolas.Williams at ubsw.com]

Looking further into this, yes, it's clear that POSIX requires
signal masks to be inherited across exec. This kinda sucks and
the standard says as much and  puts the burden of making sure
to unblock signals on the programs themselves, both parents
and children, though the emphasis appears to be on the parents
on account of many programs lacking knowledge of signal masks.

In other words, programs, such as shells, which generally
create new processes ought to ensure that signal masks are
cleared before calling exec*().

I would dare say that this applies to sshd as well and that it
does so for all signals, not just SIGCHLD.

Anyways, that is my interpretation of the text quoted below.

See: http://www.opengroup.org/onlinepubs/007904975/functions/exec.html

Specifically:

"
This volume of IEEE Std 1003.1-2001 specifies that signals set to SIG_IGN remain set to SIG_IGN, and that the process signal mask be unchanged across an exec. This is consistent with historical implementations, and it permits some useful functionality, such as the nohup command. However, it should be noted that many existing applications wrongly assume that they start with certain signals set to the default action and/or unblocked. In particular, applications written with a simpler signal model that does not include blocking of signals, such as the one in the ISO C standard, may not behave properly if invoked with some signals blocked. Therefore, it is best not to block or ignore signals across execs without explicit reason to do so, and especially not to block signals across execs of arbitrary (not closely co-operating) programs.
"

Nico
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