From: Eric Wong <normalperson@...>
Date: 2010-04-01T16:03:51+09:00
Subject: Re: socket programming...lsof?

Derek Smith <derekbellnersmith@yahoo.com> wrote:
> Hi All,
> 
> Is there a ruby substitute for lsof's functionality? 

Hi Derek,

I was wondering that today, too.  lsof is highly system-specific, so it
might not be readily implemented.  lsof and netstat (at least on my
Linux system) just parses various text files in /proc/.

**Linux only**

  Reading lsof strace output and the Linux kernel sources gave me enough
  info to get what I needed without repeatedly invoking lsof.  I found
  Documentation/networking/proc_net_tcp.txt of the Linux kernel source
  useful for describing /proc/net/tcp.  For /proc/net/unix, I had to
  read the unix_seq_show() function in net/unix/af_unix.c

  A better solution might be to use netlink (which I still want to do
  for the project I'm working on), but that involves more work than
  writing a simple text file parser in Ruby :)

> Meaning I want to
> listen on certain ports/sockets such as identd's port 113 to see if any
> process is using this port.  Is this possible in Ruby w/out using lsof?

What Roger said about trying to bind that given port (or connecting
to it, use Socket#connect_nonblock in case identd is slow to respond).

> Here is my test code, on my ubuntu personal laptop with a port from
> netstat -a.

<snip>

> host = 'localhost'

You may also want to give '127.0.0.1' a try if you're sure that port is
listening.  IIRC, some newer Linux systems favor IPv6 addresses over
IPv4 ones.

-- 
Eric Wong