s6
Software
skarnet.org
 The s6-fghack program 
s6-fghack is an anti-backgrounding tool.
 Interface 
     s6-fghack prog...
 -  s6-fghack opens a lot of file descriptors (all writing to a single pipe). 
-  Then it spawns prog... as a child. 
-  If something gets written on one of those descriptors, it's a bug in prog.
s6-fghack then complains and exits 102. 
-  Unless prog... goes out of its way to close descriptors it does not know about,
s6-fghack is able to detect when prog... exits. It exits with an
approximation of the same exit
code. 
 Notes 
 s6-fghack is what it says: a hack. Ideally, you should never have to use it.
It is only useful when you want to supervise a daemon that does not provide a
"stay in the foreground" option; and even then, the right thing is to report
this as a bug to the daemon author and have it fixed.