[geeks] Connecting two computers with serial cables - do you have to have two cables?

[Doug McLaren]

On Mon, Aug 13, 2007 at 02:00:24PM +0200, Jonathan Groll wrote:

| I would like to connect two computers together by serial cable, since
| these machines are running headless on my bookshelf, the idea behind
| using the serial cables is to offer an emergency login prompt to each
| machine should things go wrong. 
| 
| So each machine will be running a serial getty. The problem is that the
| device is locked by the getty process (at least under linux), so trying
| to launch minicom to see the other machine over the same cable results
| in "/dev/ttyS0 is locked". Is it really necessary to have two cables to
| connect two machines in this manner?

You could kill getty on the working machine and then start minicom to
talk to the other machine.  However, if getty is running on both
machines, then I'd expect them to fight with each other and keep
fighting.  By fight, they'd each keep on trying to log into each
other, stopped/slowed only by the delays getty/login inserts to
prevent dictionary attacks.

Are these machines really so difficult to reach and yet so unreliable
that you can't rely on being able to log into them via the network?

In any event, you could do it with only one serial cable I guess, but
two would be better.  With one, I'd expect both gettys to cause lots
of failed login messages, all the time.  You could kill one of the
gettys, but then if the machine that has the killed getty is the one
you need to log into, too bad.

-- 
Doug McLaren, dougmc at frenzied.us
Life is fraught with opportunities to keep your mouth shut.