Date: Wed, 19 Aug 1998 13:49:54 -0500 (CDT) From: Jeffrey Dunitz <orpheus@cray.com> To: "Robert D. Keys" <bsdbob@seedlab1.cropsci.ncsu.edu> Cc: Douglas Setzer <DSetzer@yorkcity.org>, beaupran@JSP.UMontreal.CA, cdillon@wolves.k12.mo.us, freebsd-questions@FreeBSD.ORG Subject: Re: Using a 386 with 8 Mb RAM and 300Mb HD Message-ID: <Pine.SGI.3.96.980819131939.25996I-100000@sooner> In-Reply-To: <199808191643.MAA03517@seedlab1.cropsci.ncsu.edu>
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On Wed, 19 Aug 1998, Robert D. Keys wrote:
>Date: Wed, 19 Aug 1998 12:43:11 -0400 (EDT)
>From: "Robert D. Keys" <bsdbob@seedlab1.cropsci.ncsu.edu>
>To: Douglas Setzer <DSetzer@yorkcity.org>
>Cc: beaupran@JSP.UMontreal.CA, cdillon@wolves.k12.mo.us,
> freebsd-questions@FreeBSD.ORG
>Subject: Re: Using a 386 with 8 Mb RAM and 300Mb HD
>
>> What is a Serial Console?
[quippy historical diatribe deleted] (but wait till you see me ramble on...)
Ah, the old teletype terminals...
I used to collect early glass TTYs...viewpoints, VT100s, Hazeltines...
Anyway, a small explanation of serial consoles:
For the purposes of this discussion, a server is defined as "not a workstation
but a machine that either serves files, provides services such as web or ftp,
or that people log into remotely".
Since no one is actually going to be sitting at the machine, it's a waste
to have a nice graphics system on the box. And historically, most unix
machines didn't even _have_ graphics until the mid-80's, when X started
to become popular.
So a lot of machines, before and now, use a serial terminal as a console.
You've probably used a program like kermit, or Zterm or HyperTerminal
to connect with a modem to some kind of dialup service. Those programs
emulate an acutal serial terminal. Next time you go to Home Depot, Target
or probably your local doctor's office, notice what they're typing orders
and records into--just a little monitor-like thing with a keyboard plugged
right into it, and no computer in sight. that's a serial terminal.
It's got enough smarts to talk to a modem or a direct serial connection,
and that's about it. It's not an actual computer. It doesn't have a disk
drive, card slots, or anything like that. Just a serial port, a couple
chips and a couple hundred kilobytes of memory. They usually sell for
about $400 new, of $150-200 used. Because of that, a lot of people use
old 8088 or 286 PCs as terminals, and just run kermit or procomm on them.
Before I forget, here's a major point: the only time you actually need
to do anything on your server machine that actually involves being
physically at the console is to boot the machine (and most machines
autoboot with no problem, you just turn them on and they go) or if
there's a problem when the system is coming up, or the network gets
hosed.
Since you're only going to use the console rarely, having an expensive
monitor and keyboard is silly. Using a serial terminal as a console is
a better idea.
But wait, there's more...
Using a serial console, you can also be at the console of the machine
from anywhere in the world! Here's how:
You can connect the console (serial) port of your server machine to
either a terminal server or another machine with extra serial ports,
and run kermit or a similar program on the other machine. For example,
you can telnet to your "terminal server", fire up kermit, and you're
connected to the console of your server. Another application for term
servers is as modem pools. Basically a term server is a little pizza
box with some serial ports and an ethernet port, and you can get from
a serial port to the network or vice-versa. They're useful boxes.
Where I work, we have some large Sun servers, whose console ports are
connected to a terminal server. When a machine goes down, the admins
telnet to the terminal server, and specify the port they want to connect
to (it's actually more complex than that, but for the purpose of
explanation...), and fix the machine.
So the terminal server is like this:
(serial line)
termserver-port-1 <--------------------> sunserver1-console-port
termserver-port-2 <--------------------> sunserver2-console-port
termserver-port-3 <--------------------> sunserver3-console-port
termserver-port-4 <--------------------> sunserver4-console-port
termserver-port-5 <--------------------> sunserver5-console-port
This enables the admins to not have to get up and run all the way
down to the machine room everytime something goes wrong with one
of the Suns.
Serial console is a foreign concept to most PC people, I've noticed.
What sucks about PCs is that you can't get to the BIOS from the serial
port. On a Sun, SGI, HP, whatever, if it notices that there isn't a
graphics card in the machine, or the keyboard isn't connected, all
the boot messages and "BIOS" setup stuff goes to the serial port.
In case you've never seen a non-PC unix machine's setup stuff, it's
not a "fake GUI" thing like a PC, with lots of colors and pull down
text menus and stuff. It's usually something like a >> prompt where
you type things like
> setprom netaddr 192.169.234.34
> setprom diskless false
> setprom bootimg dksc0s1p0(vmunix)
So now in contrast to all that, I'd like to say that you don't even
really _need_ to set up serial console for a machine that you're
going to play with at home and don't want a monitor for. I have
three machines in my closet at home with no monitors or keyboards, and
they don't have serial consoles set up either. If one of them screws up,
I take a spare monitor over to the closet, plug it in, and fix the machine.
This typically happens less than once per 100 days per machine, so it's
not a big deal. If I were running a full-production network with lots
of users, and large amounts of money would be lost if a machine were
unavailable, I would not want to have machines with no consoles. It
all has to do with what your needs and priorities are.
Sorry that was kind of long-winded. Serial communications is one of
my favorite topics. :)
>
>
>Surely we be kidding round the ol' java pot.....(:+}}.....?
Just felt the need to clarify for the benefit of our (apparently)
young friend who may not remember printing terminals. :)
>
>RDK
>
>
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Jeffrey Dunitz (orpheus@cray.com) 612-683-7266 | it's hard times
Information Services <http://wwwis.cray.com/~orpheus>; | befallen the
===== Cray Research, now Silicon Graphics = == === === =====| sole survivors.
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