SUMMARY: Disable prom mode on loss of console.

From: Carlo Musante (
Date: Thu Feb 24 2000 - 19:57:53 CST

My original question:

> I have a cluster of Sun's connected by a terminal server which just died.
> Is there a way to keep the Sun's from dropping into the Bootprom without a
> keyboard or serial terminal?

Solution and Summary:

There were two solutions to solve I used to solve the problem. On
Enterprise type Suns like E3550, E450, etc... the power switch has four
positions, off, on, diagnostic and secure (in that order). With the power
switch in the secure position the breaks generated by, keyboard reconnect,
serial terminal loss, Stop-a or a serial terminal break key are ignored.
Using the switch is prefered incase the system locks up you can turn the
power switch to the on position and send a break from the keyboard.

On Sun's with out the benefit of the secure switch (tested it on Sparc10)
you need to be running at least Solaris 2.6. Then you can use the kbd
command and the config file /etc/default/kbd. In /etc/default/kbd add the
variable "KEYBOARD_ABORT=disable" then use the command "kbd -i" which
reads /etc/default/kbd and disables keyboard abort. You can also toggle
between enable and disabled using "kbd -a disable" and "kbd -a enable".
The man page on kbd describes it in more detail if needed.

The draw back to kbd is if the system locks up the power switch is the
only way to recover.

On older systems running Solaris pre2.6 and SunOS I received no
suggestions but found some answers in the archive.

Hardware: There were refrences to a circuit which could be placed on the
serial port to keep it active but no links were given. Also placing a
4.7k resistor between pin 3 and pin 25 on the serial port was suggested.
It was suggested that a good terminal server will not cause the attached
Sun's to boot. Maybe htey would have passive circuitry which keeps the
Sun's up when they fail. Will have to make sure this feature exists on
new hardware should money be budgeted for upgrades.

Software: Use adb to hack the zs driver to insert a nop (no operation)
instruction in the BREAK handling routine. Details were not provided.
Some one mentioned a Solaris patch put did not give a number and I
couldn't find one.

I also received a reply which suggested installing a package from Sun
which can remap the break sequnce called SUNIzsbrk. I don't think
remapping would solve the problem since the break handling routine would
still be active.

Below are the reply's I received, I thank everyone who replyed for their



From: "Carsten B. Knudsen" <>
Subject: Re: Disable prom mode on loss of console.

Hi Carlo,

  Uh oh, tough-- I have done just that a couple of times, but I am lucky
to be in a non-7x24 environment, so while it was a (huge:-) bit
inconvenient, noone was really hurt; power back on, telnet to the box,
type "go", disconnect, next port etc. and I was back on track after a
minute or two.
  Anyway, back to the real question: If you have Solaris 2.6 (or higher I
guess), you can run "kbd -a disable" to disable L1-A/BREAK. Or if your
Sun is big enough, it might have a front panel key to disable the abort
key. In other cases, I think you're out of luck; if you find out
differently, please tell me ;=>>

best regards,


  Carsten B. Knudsen Email:
  TERMA Elektronik A/S Phone: +45 8743 6000
  Hovmarken 4-6 Fax: +45 8743 6001
  DK-8520 Lystrup, Denmark (@home:
#include <generic/std_disclaimer.h>


From: Stefan Voss <>
Subject: Re: Disable prom mode on loss of console.


in Solaris 2.6 or later, you can type "kbd -a enable|disable" or put
"KEYBOARD_ABORT=enable|disable" in /etc/default/kbd. This does not only
enable/disable the STOP-A keyboard abort sequence, but also prevents the machine
from going to prom mode, if the serial console is powered off. See the man page
for kbd for more details.


                                     (o o)

  Stefan Voss Phone: 0049 / (0)5130-9775-51
  System and Network Administration Fax: 0049 / (0)5130-9775-10
  TerraData Geophysical Services GmbH e-mail:
  Zoellners Garten 1
  D - 30900 Wedemark (OT Bissendorf), Germany


Subject: Antwort: Disable prom mode on loss of console.

I had a similar problem yesterday (inadvertently). You can prevent your box from
crashing upon loss of the console (pulling out the keyboard cable or turning off
a vt-terminal attached to the serial port) by turning the power key on the front
panel to the 'locked' position.

best regards

Benedict de Silva


From: Mark Olson <>
Subject: Re: Disable prom mode on loss of console.

If you have the correct terminal server this will not happen.

I use an Xylogics (Nortel/Bay Networks) Annex 3 on my Sun E450 server
and can power cycle the terminal server w/o affecting the E450. On
server class machines like the 450 you also have a keyswitch that can
disable dropping into the boot prom on receiving a break, and I believe
there is also an eeprom setting to ignore breaks, although I would
avoid that because it gives me no way of dropping to the OK prompt
remotely if the system is hung.


Mark C Olson               |
ADC Telecommunications     |telephone: +1 612 936 8008
PO Box 1101, MS 125        |      FAX: +1 612 936 8333
Minneapolis MN 55440-1101  |


From: "Rasana Atreya" <> Subject: Re: Disable prom mode on loss of console.

I believe there is. Search the archives.



From: Goodson Alex A <> Subject: RE: Disable prom mode on loss of console.

If you've got a key on the server turn it to secure mode that should do the trick.




From: "Halverson, Mark" <> To: "'Carlo Musante'" <>

apparently it depends on which suns you have. I understand the 450's can avoid the hang by turning the key to the locked position.


From: "Vishnu Murthy" <> Subject: Re: Disable prom mode on loss of console.


Try this packge, with this u can change the break character..


PKGINST: SUNIzsbrk NAME: SunIntegration CONSULT-ZSBRK (Serial Number: 97061780) CATEGORY: system ARCH: sparc.sun4m VERSION: 2.2.2 BASEDIR: / VENDOR: Sun Microsystems, Inc. DESC: This package contains the SunIntegration CONSULT-ZSBRK special PSTAMP: kenobi970409154215 INSTDATE: Aug 29 1998 05:48 HOTLINE: 1-800-225-4449: or contact your local service provider EMAIL: swspec@Sun.COM STATUS: completely installed FILES: 10 installed pathnames 6 shared pathnames 7 directories 3 executables 142 blocks used (approx)

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