How can a parent find out if one of its children is still alive

[Steven Bellovin]

In article <1046 at gargoyle.uchicago.edu>, matt at group-w.uchicago.edu (Matt Crawford) writes:
} ) DeadHead at cup.portal.com (Bruce M Ong) writes:
} ) > 	How can a parent find out if one of its children is still alive
} ) > or not without
} 
} Tom Armistead, wizard-wannabe, answers:
} ) i.e.:   if( kill( child_pid, 0 ) == -1 )
} )             puts( "The child is dead" );
} 
} overlooking the possibility that the child exited many minutes ago and
} the pid is now being used by some unrelated process.

You can look at errno to determine if the kill() failed because of
a uid mismatch.  That will yield a lot of info if root isn't doing
the checking.