Re: What is the process group hack

[Charlie Brady <charlieb-smarden-supervision@budge.apana.org.au>]

On Thu, 26 Apr 2012, Wayne Marshall wrote:

> fghack is djb's "anti-backgrounding" utility.  It invokes
> strangeness and mysteries to inhibit a process from forking into
> the background.

No, it doesn't change anything about the way the process operates. It just 
starts the process in a child process, and attempts to stay around until 
that process exits. 

See the description here:

http://cr.yp.to/daemontools/faq/create.html

fghack creates a pipe from the daemon and reads data until the pipe is 
closed. Normally all the daemon's descendants will inherit the open pipe 
from the daemon, so the pipe will not be closed until they all exit.

However, fghack will exit early if the daemon goes out of its way to close 
extra descriptors. A few of these daemons leave descriptor 0 open, even 
though they do not use descriptor 0; so

     #!/bin/sh
     exec fghack baddaemon <&-

might work.