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Re: Serial Connection -- shielding

On Thu, 31 Mar 2011 09:14:07 -0400 (EDT), MAROUNI Abbass wrote:
> In a production environment, this what will happen :
> Two servers connected with a single serial cable ( Which I need to 
> figure out how?! :) ), ttyS0 on server1 to ttyS0 on server2.
> getty is always listening to the ttyS0 port on both servers (assured by 
> inittab respawn).
> Server1 is inaccessible. login to server2 launch a script that will kill 
> getty and comment its entry from inittab then launch minicom toward 
> ttyS0 on server1 login to server1 and find what happened. Finally on 
> server2 quit minicom launch another small script that would put getty on 
> ttyS0 and uncomment its entry from inittab. This way if something wrong 
> happens to server2 I am sure that I have a getty on its ttyS0 and all I 
> need to do is to go to server1 follow the same procedure.
> Reverse communication assured :)
> Logical isn't? :)
> I am still not convinced that the serial cable might have different ends 
> if it's a standard null modem cable, so I don't think that reversing the 
> ends between the two servers might help.

OK, now I think I understand.  I have some more thoughts, but before I
share them I want to address your attitude.

Suppose you were a medical doctor.  Suppose I came to you with a problem.
For the sake of example, let's say that I am complaining of a sore throat.
You use a tongue depressor and a flashlight and look at the back of my
throat.  It's deep red and very swollen.  You take my temperature.  I have
a fever.  You think the problem is strep throat.  So you write me a
prescription for an antibiotic.  I thank you and leave your office.  Three
days later I come back in, complaining that my throat is worse than
before.  You ask me if I have been taking the medicine that you prescribed
according to directions.  I say, "No, in fact I didn't even bother to
fill the prescription."  What would your reaction be?  How motivated would
you be to continue trying to help me?  I dare say, not very motivated.
If I had taken the medicine but the problem grew worse, you would be
even more motivated to help me.  But if I wouldn't even try what you
suggested, I dare say your reaction would be, "Fill the prescription
and take the medicine according to my directions.  If you don't feel
better in three days, come back and see me."

You are acting just like that.  People ask you for specific information.
You don't provide it.  Someone suggests that you try something, but you
don't try it because "you don't think" that that is the problem.  Well,
if you're so smart, why are you asking for help?  How hard is it to reverse
the cable, for diagnostic purposes, just to see if it makes a difference?
You won't try anything.  Now I have an idea of what the problem might
be.  It might be the solution.  Or I might be barking up the wrong tree.
But I'm not going to share it with you until you try what I've already

Reverse the cable and see if makes any difference.  Let me know the
results of the experiment.  Then maybe I'll suggest something else to try.

  .''`.     Stephen Powell    
 : :'  :
 `. `'`

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