From: Robert Klemme <shortcutter@...>
Date: 2012-02-02T20:59:25+09:00
Subject: Re: Starting a process and specifying its parent

On Thu, Feb 2, 2012 at 8:29 AM, Victor Blaga <vic.blaga@gmail.com> wrote:
> I need to start a (sub)process from inside a ruby script that will continue
> to run after the ruby script itself has finished.
> The way I'm doing stuff right now is by using Process.spawn - this works,
> however the ppid of the child process is assigned to the script that was
> used to start the process, and thus after the script finishes the spawned
> (child) processes gets closed as well.

No.  Storing the PID of the child somewhere and stopping the child
process are completely unrelated:

12:54:32 ~$ ruby19 -e 'p Process.spawn("bash", "-c", "sleep 10; echo
from shell; date"); puts "from ruby #{Time.now}"'
228
from ruby 2012-02-02 12:54:41 +0100
12:54:41 ~$ from shell
Thu, Feb 02, 2012 12:54:51 PM

It must be something else which terminates the child.  Do you close
the terminal?

> My question is what would be the best way to start such a (sub)process and
> assign it a parent in such a way that it keeps running even after the
> current script has ended? As a side-note, I also need to be able to capture
> the stderr and assign it to a specific file (which works using
> Process.spawn), but I'm not sure about the other methods.
> I have to mention I'm using a linux machine but I'm unfortunately not very
> familiar with the way linux process exactly work...

You could do

fork do
  $stdin.close
  $stdout.reopen "/dev/null"
  $stderr.reopen "/tmp/errors"
  exec "your_command", "with", "arguments"
end

You'll find more by searching for "demonize".

Kind regards

robert


-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/