Getting the parent id of a given process in Ruby

Question

How do you get the parent process id of a process that is not the current process in Ruby?

I've checked Ruby's Process module, but it only seems to provide a means to access the PPID of the current process.

I also checked google for anything on the subject, but the first two pages seemed to only contain links regarding how to use the aforementioned Process module.

I was hoping to do this without having to rely too much on the underlying OS, but whatever works.

Answer 1

You can just remember it in a variable:

parent_pid = Process.pid

Process.fork do
  child_pid = Process.pid
  puts parent_pid, child_pid
  # do stuff
  exit
end

Process.wait

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alternatively, if you need the information on the level of the parent process:

parent_pid = Process.pid

child_pid = Process.fork do
  # do stuff
  exit
end

Process.wait
puts parent_pid, child_pid

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Answer 2

Shell out:

1.9.3p429 :001 > `ps -p 7544 -o ppid=`.strip
 => "7540"

Answer 3

Process.ppid returns the parent process id. http://ruby-doc.org/core-2.4.1/Process.html#method-c-ppid