Multiple serial consoles via null modem cable

Thu Jan 21 09:37:10 UTC 2010

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]

> This means that login prompts for box1 will be spawned/available on both
> serial ports (ttyu0 and ttyu1).
>
> If you get on box2 and do "cu -l ttyu2", this will connect you to box2's
> COM3 port, which is physically connected to box1's COM1 port.  Hit enter
> and you should see a login: prompt for box1.
>
> The same applies if you get on box2 and do "cu -l ttyu3" (but for box2's
> COM4 port, which is wired to box1's COM2 port).
>
> With the above configuration in mind, you SHOULD NOT:
>
> - Mess with /etc/ttys on box2
> - Execute "cu -l ttyu0" or "cu -l ttyu1" on box1 -- this probably won't
>  work (likely will return some message about the device being locked or
>  in use already).
>
> You cannot do something like where box1 COM1 is wired to box2 COM1, and
> depending on what box you're on doing the "cu -l ttyu0" from, get a
> login prompt on the other.  It doesn't work like that.  :-)
>
> Now, about actual *serial console* itself -- that is to say, kernel
> output during boot, etc... on a serial port.  AFAIK, on FreeBSD you can
> only set serial console to a single serial port, and that defaults to
> COM1/ttyu0.  You can change what port/device, but there can only be one.
>
> Yes, probably I didn't explain myself better, but you did it good - what I
was trying to say is that I can use only one COM port for serial console,
which of course defaults to COM1.

Also is conserver/conserver-com able to handle more than one serial consoles
on a machine? I haven't tried conserver yet.

Thanks for the good explanation again :)
Marin

> HTH...
>

Now

>
> > On Sun, Jan 17, 2010 at 3:32 PM, Ronald Klop <
> ronald-freebsd8 at klop.yi.org>wrote:
> >
> > > On Fri, 15 Jan 2010 07:34:17 +0100, Marin Atanasov <dnaeon at gmail.com>
> > > wrote:
> > >
> > >  Thank you a lot for your feedback!
> > >>
> > >> Now to the real question again, because I'm a little confused now -
> can I
> > >> still get a usb-to-serial port converter having let's say 8 serial
> ports
> > >> and
> > >> then connect each machine to the usb-to-serial hub and manage them
> > >> remotely
> > >> from a single location (the host having the usb-to-serial hub)? That
> way I
> > >> just specify a serial port number and I get to a specific machine?
> > >>
> > >> The model provided by Boris looks nice, and that was my initial idea,
> but
> > >> I'm not sure if I could get it working under FreeBSD. Is conserver or
> > >> conserver-com able to handle this? I know that cu uses COM1 only, but
> will
> > >> conserver able to handle serial consoles on different ports, since the
> > >> usb-to-serial port would appear as multiple serial ports.
> > >>
> > >
> > > You can provide cu with the port to connect to on the command line.
> > >
> > > cu -l cuaU0 -s 115200
> > > cu -l cuaU1 -s 115200
> > > etc.
> > >
> > > You can not connect several servers on 1 serial port, but you can
> connect
> > > several servers on several serial ports. With serial-over-usb it scales
> to
> > > many serial ports.
> > >
> > > Ronald.
> > >
> > >
> > >> Thank you and regards,
> > >> Marin
> > >>
> > >>
> > >> On Tue, Jan 12, 2010 at 7:04 PM, Boris Samorodov <bsam at ipt.ru> wrote:
> > >>
> > >>  On Tue, 12 Jan 2010 17:14:44 +0200 Marin Atanasov wrote:
> > >>>
> > >>> > I'm thinking about the following situation - 1 system acting like a
> > >>> host
> > >>> > with a serial port hub, each port of the hub is connected to a
> > >>> different
> > >>> > machine on sio0, using null modem cables.
> > >>>
> > >>> Along with milti-io serial cards we use multi-usb serial
> > >>> converters, such as SUNIX UTS7009P (7 USB to serial adapter):
> > >>> http://www.sunix.com.tw/it/en/LinkCraft/UTS4009P_UTS7009P.htm
>
> --
> | Jeremy Chadwick                                   jdc at parodius.com |
> | Parodius Networking                       http://www.parodius.com/ |
> | UNIX Systems Administrator                  Mountain View, CA, USA |
> | Making life hard for others since 1977.              PGP: 4BD6C0CB |
>
>

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