SUMMARY: Unplugging keyboard on SUN SS20 and Ultra 2

From: Francisco Javier Arias Correa (NIC) (
Date: Fri Jun 12 1998 - 17:01:51 CDT

Especial thanks to:

        Jeff Wasilko and Caleb Warner.

Also thanks to:

        Rich Kulawiec
        Bismark Espinoza
        Tom Erickson
        Matthew Stier
        Maurice Levie
        Raymond Wong
        Scott McDermott
        David Thorburn-Gundlach
        Aaron Lineberger
        Walsh, Dave
        Tom Bernard
        Chris Marble
        Damir Delija
        Leif Ericksen

------------------- Original question -------------------

> When unplugging the keyboard on a Sparc Station 20 and a Ultra 2
> the system stops and the PROM's prompt "ok" apears.

        It should say: When unplugging and plugging the keyboard ...

> 1) Does anyone know why this is happenning?
> 2) Does anyone know how I could avoid this to happen?

----------------------- SUMMARY -----------------------------------

        1) When you unplug and plug the keyboard on a Sun a break signal
is generated (like stop-A) causing the system to stop and the ok prompt to

          - In Solaris 2.6 type: kbd -a (I do not have such a system so I
could not do it).

          - With Solaris 2.5.1 (the one I have) there exist a
software package (P/N CONSULT-ZSBRK), but it is not for free, so you
should have to buy it from Sun.

          - There is a workaround: to buy a switch that allows to share
keyboard, mouse and monitor between systems.


From: Jeff Wasilko <>

If you are running 2.6, use kbd -a disable:
     -a enable/disable state
                       Enable or disable the keyboard abort
                       sequence effect.
                       By default, a keyboard abort sequence
                       (typically, Stop-A or L1-A on the keyboard
                       and BREAK on the serial console device)
                       suspends the Operating System on most sys-
                       tems. This default behavior can be
                       changed using this option. This option can
                       only be used by the superuser.

                            Enable the default effect of the key-
                            board abort sequence, which is to
                            suspend the operating system and
                            enter the debugger or the monitor.

                            Disable the default effect and ignore
                            keyboard abort sequences.


>>>>> Is there any solution with Solaris 2.5.1?

Not that I'm aware of.

There are keyboard switches that allow you to switch a keyboard
from system to system w/o halting them...



From: Caleb Warner <>

When the keyboard is unplugged nothing should happen, however when the keyboard
is plugged back in a "Break" signal is sent to system. The break signal causes
the system to drop to the ok prompt as if "STOP-A" had been typed on the
keyboard. Typing "GO" at the okay prompt will cause the system to continue most

Unless things have changed recently, for Solaris 2.5.1 and below you can buy
from Sun Consulting a software package (SUNIzsbrk) that will allow you to
disable this feature. By the way this was outrageously priced last time I
checked into it.


From: bismark@alta.Jpl.Nasa.Gov (Bismark Espinoza)

Suns see a BREAK commmand as a command to enter prom mode.
Get a terminal server that does not send a BREAK when turned
off, put a resistor pulling up one of the rs232 lines, or get
an E4000 that has a console key that disables this "feature".


From: Matthew Stier <>

1) Sun keyboards (and mice) are serial devices, and communicate to the
CPU thru a serial port. The serial communications protocol which defines
the timing and patterns used to communicate character over a serial link,
also define a "break" condition. An "out-of-band" condition, when the
serial in line goes from it quiescent state, to space state for a period of
several character cycles. (1/4 to 1 second) [This "break" is what happens
when you press the "break" key on a terminal.]

The "break" condition is interpreted in hardware, in the serial port, and
sent to the CPU via a Non-Maskable Interrupt [NMI]. The Sun is programmed
to interrupt the computer, and place it in the prom monitor state when this

This "break" happens when you unplug, or plugin a keyboard, because the
keyboard cable also has the power and grounding for the keyboard, and it is
possible to pull the serial in line down long enough for the serial port
the keyboard is plugged into, to believe that a break condition exists.


From: David Thorburn-Gundlach <>

In my experience, unplugging the keyboard from an sbus system (ss20,
u2, e4k, etcetc) has no effect on the system, but plugging it back in
(even if it was booted without one) generates a "beep" and the ok
prompt. On the other hand, unplugging the keyboard from a pci system
(u5, u10, u30) generates no feedback (ok prompt, beep, etc) but *does*
freeze up the system; when you plug a keyboard in, you get the typical
beep and ok prompt -- but it's a bit late by that time :-)


From: "O'Neal,Chris" <>

Can't talk about the Ultra2, but the SS1 thru SS20 do reboot if the
console head (keyboard, mouse, video) is disconnected. It just what
Suns do, I don't think they see this as a problem.

Here we run a NULL modem cable off ttya to a terminal server which has
one keyboard-mouse-crt. It save table space.


From: Chris Marble <>

As far as I know the break signal gets sent automatically when the
keyboard is unplugged. Our workaround is to just use a terminal on
the serial port of the machines in the machine room. The boxes stay
headless. We just move the terminal around serial port to serial port
as we need console access.


        Francisco Javier Arias Correa
        NIC-Mexico, ITESM campus Monterrey
        Tel. +52 8 328 43 73, fax +52 8 328 42 08

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