SUMMARY: switch to allow many machines to share one console

From: Charles Chip Buchholtz (
Date: Wed Jun 15 1994 - 17:38:39 CDT

I asked:

: I'm looking for a serial switch which will allow four or more Sun
: servers to use one dumb terminal as a console. I don't want to buy
: frame-buffers for each machine, and I don't want to clutter my
: machine-room with separate console terminals.

: I'd prefer not to use a terminal server approach.

Thanks to:

                         heas <>
                 Gregory Bond <>
                   Ric Anderson <ric@Artisoft.COM>
                   Gene Rackow <>
     (Barnes William)
     (Leslie_B_Dreyer Kalra)
          (Nick Nickerson)
       (Sanford Whitehouse)
      (Mark Foster)
             Kambiz Aghaiepour <kxaghai@srv.PacBell.COM>
    (Paul T. Keener)
    (Suzanne Bryant)

Many people advised staying with many dumb terminals, because
important diagnostic messages will be lost when console is switched
elsewhere (but see below).

Others suggested using a terminal server, because this gives greater
flexibility, in that you can connect from anywhere on the network to
any console, and two people can use two consoles simultaneously. I'm
concerned with rebooting after a power failure, however; I want to
avoid deadlock problems where the server won't boot until it has a
console, and the terminal server won't boot until its server is up.
Also, there is the "lost messages" problems mentioned earlier.

Another possibility is using a standard serial switch, adding a
circuit to allow you to switch consoles without dropping into prom
monitor. This is an inexpensive and robust solution, but still loses
console messages from unhooked machines. NuData has a such a switch
with the special circuitry built in.

There are also programs that can be run on one machine (Sun or PC) to
act as the console for other machines. This will work fine if the
console machine is independent of the others.

Similarly, you can daisy chain ttya to ttyb on each system, and use
tip. However, losing one machine will isolate the downstream
machines, and I imagine that rebooting all machines simultaneously
after a power failure could be interesting.

Black Box has a switch which prints all of the data from all of the
machines, prefixing each line with a tag indicating the source. Typed
input can be prefixed with the desired destination, or you can switch
the default destination when working continuously on a single machine.
This seems to be a perfect solution, as there are no booting problems
and no undisplayed messages.

Western Telematic has an even better (and more expensive) solution
called "CPM-1600". This provides many to many connectivity, and
buffers up undisplayed output for later display. So, you could have
two terminals and 10 machines, and hook the terminals to whichever
machine you wanted.

Although these last two solutions don't lose any messages, they don't
eliminate the problem completely. I'm concerned that I will come in
one morning to find one system hung, and the console (or buffer)
filled with "/home6 quota exceeded" messages from the healthy systems.
After considering all of these options, I'm strongly considering
finding desk space for one dumb terminal per system.

Thank you all for contributing. The complete texts of the messages
are appended below, and contain prices, addresses, names, FTP sites,
and other details.

Charles H. Buchholtz
Systems Programmer (215) 898-2491
School of Engineering and Applied Science 200 S. 33rd St, rm 154
University of Pennsylvania Philadelphia, PA 19104


From: heas <>

        don't do either, and have the convienence of connecting remotely....
use an annex terminal server from xylogics, burlington mass. 617-272-8140.

        the annex would have a serial line for each machine. you can then
telnet to the annex, select a port, deal with the optional security, and just
as if you were right there.....from home/cube.



From: Gregory Bond <>

The worst problem with this sort of approach is that when you _really_ need to
see what's on the console (e.g. machine hung or panicking), you inevitably
find that the switch is set to another host and you've lost that vital

Much easier to just use four terminals.


From: Ric Anderson <ric@Artisoft.COM>

The Black Box Catalog folks used to carry an MCTE (Multiple
Console Terminal Eliminator). It was a 4 (or 8) port
box with one output, and it printed data from all input
ports prefixed by the port number. You could make a connection
to a specific port if you needed to type to it.

Advantage over an A/B/C/D switch is you don't loose output
from Machine A while switched to Machine B.



A serial switch-box (or several) can do the trick. However, you lose
any logging that would have gone to the terminal, which you can cover
for some by appropriate syslog configuration, but not completely.



You might consider rewiring a printer switch box for serial.

But it IS a lot more convienient to use dumb terminals.


From: Gene Rackow <>

A console server program is available from the ohio-state and purdue archives.
This would allow you to connect the console cables from other machines to
one machine. The advantage here is that you can get full logging of the
console ports of the other machines. You also get access to the console
ports from remote locations.. ie you don't have to go to the machine room
to see what is wrong and reboot. ;-) I'd strongly recommend doing that
as compared to the black-box brand of rs-232 switches.


PS: if yuou need exact ftp locations, I can dig them out for you, or
send you a copy of our sources. We modified ours to work with the annex
terminal server as the connection point and the "conserver" program works
over the net.


From: (Barnes William)

We have used just standard RS232 switch boxes to switch a vt100
between one of say 5 servers. It is nice to have less tubes, but one
thing that I miss is that you do not get the messages that were sent
to the screen if the terminal is switched off that machine. You know
Murphy, it always turns out that the server you want the old
information is the one that it is switched away from.


From: (Leslie_B_Dreyer Kalra)

NuData, in NJ, has just the thing. It's a switch that allows
you to run up to five machines from one console, or vice
versa. They have two versions: one for dumb terminals, one
for bitmap displays. We have the bitmap version, but we haven't
put it into use yet. The dumb terminal one is supposed to
"fool" the circuitry into thinking there is a console attached
to the serial port at all times, even when the switch is set

NuData's catalog is called "Workstation Express". The item is
called a "Server Monitoring Switch". Prices are as follows:

4266 5 to 1 Sun Server Switch $695
4269 5 to 1 Serial Console Switch $395 <<---
4267 1 to 5 Sun Server Switch $695
4268 5 to 1 Solbourne Server Switch $695

Phone: (908) 842-5757
Fax: (908) 842-1161

Hope this helps. BTW, I'm not affiliated in any way with NuData
or Workstation Express. I just haven't found such a device
anywhere else...

Leslie Dreyer Kalra
Allentown, PA



We just ordered a "CPM-1600" from Western Telematic. Here's some of the
specs :

- 16 Ports
- Any-Port to Any-Port switching
- Password Protection
- 512K non-volatile dynamic buffer
- Data & Speed conversion
- Auto Routing
- Can access each port by number or assigned name. (console1, console2, etc.)
- Collects output from consoles that you are not currently monitoring for
  later access.

They list the following as possible applications :

- Out-of-band Network Management
- Data Communications Controller
- Remote Diagnostics Port Selector
- Modem Management
- Statistical Data Collection/Storage

We plan to use it in the fashion you suggest. (Consoles for a Sun 4/280,
Sun 4/380, A router, a term server, a few hubs, etc...) We really only
want one or two terminals and moving cables around has gotten real old. :-)

The cost is $995. Contact Mike Moss at Western Telematic 1-800-854-7226 x223.
Again, we haven't actually used this device yet. It's due to arrive this
week... If you like I could let you know what I think of it after we
actually have it installed...


From: (Nick Nickerson)

        We have used a device from Black Box that takes 8 serial line inputs
and displays them on a single terminal (VT100 type). These are about 5 years
old but were fairly cost effective at that time. You can even option them so
a different "tag" appears next to each line of output, thus identifing the source.

Input is controlled by prepending the "tag" on the command line. If you need
to work with one system exclusively, I seem to recall you can direct the box
to "switch" to just that system.

I would guess that Black Box still offers these or an equiv. unit.


From: (Sanford Whitehouse)

We are currently using two 4 port serial cards in a pc to
do console for our hps and sun. We purchased the software
and hardware from Network Wizards for ~$800 (sans pc).

Network Wizards
1055 Pine St.
Menlo Park, CA
(415) 326-2060
Fax:(415) 326-4672


From: (Mark Foster)

I just saw a product in NuData that sounds like exactly what
we'd like (they actually have several models, but one of
them seemed to fit the bill the best):

4269 5 to 1 Sun Serial Console switch $395.00

NuData isn't always the cheapest, but I'd bet this product is
only about 10% cheaper elsewhere. An advantage to NuData is
that you could probably have it the day after you give them
a p.o.#.

The above switch allegedly has circuitry to avoid generating
a "break" when you switch from one system to another.


From: Kambiz Aghaiepour <kxaghai@srv.PacBell.COM>

To get your four consoles, do the following:

 serverA|ttyb<-->ttya|serverB|ttyb<-->ttya|serverC|ttyb<-->ttya|serverD ...

Connect the ttyb port of one machine to the ttya of the next. In this
way you can obtain console on serverB by connecting to serverA and
attaching to ttyb (tip hardwire). Similarly you can connect to serverB
and attach to ttyb (tip hardwire) to obtain console on serverC and so


From: (Paul T. Keener)

I have a small circuit that allows you to disconnect the console terminal
from the serial port with out the machine dropping into prom. Once you
put that in on each machine, you can use a normal serial a-b (c-d) switch.


From: (Suzanne Bryant)

        I spend a great deal of time looking for a serial solution. You
might try ARNET, they usually have good products. I however, chose to goto
a terminal server. This, for us, has worked extremly well as I can access the
console from both a GUI and a telnet connection and via modem. I am using the
SUN terminal server/software which was very inexepensive.

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