Multiple serial consoles via null modem cable

[Marin Atanasov]

On Fri, Jan 22, 2010 at 10:02 AM, N.J. Mann <njm at njm.me.uk> wrote:

> In message <717f7a3e1001210137p7884adcbxc66a4f7fff928821 at mail.gmail.com>,
>         Marin Atanasov (dnaeon at gmail.com) wrote:
> > Hello Jeremy,
> >
> > Now I'm a little confused :)
> >
> > I've made some tests with my machines and a couple of null modem cables,
> and
> > here's what I've got.
> >
> > On Wed, Jan 20, 2010 at 9:46 AM, Jeremy Chadwick
> > <freebsd at jdc.parodius.com>wrote:
> >
> > > On Wed, Jan 20, 2010 at 08:46:48AM +0200, Marin Atanasov wrote:
> > > > Hello,
> > > >
> > > > Using `cu' only works with COM1 for me.
> > > >
> > > > Currently I have two serial ports on the system, and only the first
> is
> > > able
> > > > to make the connection - the serial consoles are enabled in /etc/tty,
> but
> > > as
> > > > I said only COM1 is able to make the connection.
> > >
> > > I'm a little confused by this statement, so I'll add some clarify:
> > >
> > > /etc/ttys is for configuring a machine to tie getty (think login
> prompt)
> > > to a device (in this case, a serial port).  Meaning: the device on the
> > > other end of the serial cable will start seeing "login:" and so on
> > > assuming you attach to the serial port there.
> > >
> > > For example:
> > >
> > > box1 COM1/ttyu0 is wired to box2 COM3/ttyu2 using a null modem cable.
> > > box1 COM2/ttyu1 is wired to box2 COM4/ttyu3 using a null modem cable.
> > >
> > > On box1, you'd have something like this in /etc/ttys:
> > >
> > > ttyu0   "/usr/libexec/getty std.9600"   vt100  on secure
> > > ttyu1   "/usr/libexec/getty std.9600"   vt100  on secure
> > >
> >
> > Here's what I did:
> >
> > box1 COM1/ttyd0 -> box2 COM1/ttyd0 -> using null modem cable
> > box1 COM2/ttyd1 -> box3 COM1/ttyd0 -> using null modem cable
> >
> > On box1 I have this in /etc/ttys:
> >
> > ttyd0   "/usr/libexec/getty std.9600"   vt100   on secure
> > ttyd1   "/usr/libexec/getty std.9600"   vt100   on secure
> >
> > Now if I want to connect to box1 from box2 or box3 through the serial
> > connection it should work, right?
> > But I only can connect to box1 from box2, because box2's COM port is
> > connected to box1's COM1 port.
> >
> > >From box2 I can get a login prompt
> > box2# cu -l /dev/cuad0 -s 9600
> > Connected
> >
> > login:
> > )
> > (host.domain) (ttyd0)
> >
> > login: ~
> > [EOT]
> >
> > But if I try to connect to box1 from box3 - no success there.
> > box3# cu -l /dev/cuad0 -s 9600
> > Connected
> > ~
> > [EOT]
>
> You need to reduce the number of unknowns, e.g. where is the problem:
> box1, box3 or in between.  So, swap the cables on box1 so that you now
> have box1:COM1 -> box3:COM1 and box1:COM2 -> box2:COM1.  Now repeat the
> tests above and post your results.
>
>
> Cheers,
>       Nick.
> --
>
>
Seems I've found the issue, that I'm having - a broken null modem cable :(

The last time I was using that cable it was working fine. And now that I
connected a second one to the machine, it seemed that only the one connected
to COM1 was actually working, and I was left with the impression from the
documentation that only COM1 is able to do a serial console connection.

I'm very sorry to bother you like that. I'll continue setting up the servers
once I get a new null modem cable.

Thanks and regards,
Marin

-- 
Marin Atanasov Nikolov
dnaeon AT gmail DOT com
daemon AT unix-heaven DOT org