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NOTES
       A child that terminates, but has not been waited for  becomes  a  "zom-
       bie".  The kernel maintains a minimal set of information about the zom-
       bie process (PID, termination status, resource  usage  information)  in
       order to allow the parent to later perform a wait to obtain information
       about the child.  As long as a zombie is not removed  from  the  system
       via  a wait, it will consume a slot in the kernel process table, and if
       this table fills, it will not be possible to create further  processes.
       If a parent process terminates, then its "zombie" children (if any) are
       adopted by init(8), which automatically performs a wait to  remove  the
       zombies.

So, as long as the parent is alive, defunct children will be kept around.

If it is not possible/convenient to have the parent wait on the
children, the parent should fork off grandchildren (instead of
children) as follows:

1) Parent forks child and calls wait
2) Child forks grandchild
3) Child exits causing parent's wait call to return
4) <time passes>
5) Grandchild exits.  Child is already dead, so init adopts grandchild
and calls wait.  Grandchild is then automatically removed.

-mpb