Console Server - issues

[joe_91]

Team:

Good Day!!!

When a lantronix console server is rebooted it sends a break signal to all the servers connected to it. This may cause the Server to panic/suspended state/reboot. There is a way the OS can disregard this by having an alternate keyboard sequence enabled in some files under /etc. does someone know a way around this so that the console server can be rebooted without affecting the servers. i just saw the kbdlang file nothing else under /etc.

Best Regards

Joe

[Mel Burslan]

Joe,

I am not sure what type of servers you have, connected to this lantronix console server and what break sequence is in question here but I do not remember a server that I dealt with for a long long time where a break or any other keystroke caused a server to panic/reboot.

If you can tell your exact situation with the servers and OS versions in question, you can get better answers. But if you are running servers built in the last decade or so, your worries are unfounded. To reboot a server from the console, it takes much more than a simple break sequence to be issued.

[Matti_Kurkela]

As far as I know, the problem you describe affects only Sun Solaris operating systems on a SPARC-based hardware architecture.

With default settings, reception of a BREAK signal to the console serial port drops the Solaris server to the firmware "ok>" prompt (roughly equivalent to the PDC prompt in HP-UX), freezing the OS. The SPARC hardware can resume OS execution from this state, and a simple command will do just that. However, if the system has been frozen for a long time, the applications may not handle the situation correctly.

HP-UX simply does not do that. This is a non-issue for HP-UX servers.

In modern HP-UX hardware, the only "special" things on the console are keystrokes Ctrl-B and Ctrl-A (the latter only if vPar partitioning is in use). Neither of those do anything immediately harmful. Ctrl-B interrupts the console session and allows the console user to access the management processor. The management processor can be given further commands to halt or reset the server, but any dangerous actions will request a confirmation first. Ctrl-A just switches the console view from one virtual partition to another.

[Volker Borowski]

Matti is right,
I know this from Sun as well.
The problem is, that the console is usually defined as a boot-device (strange what?) and if Solaris is loosing it you'll get a panic.

Funny: disconnect console and boot -> no boot device -> system is running -> plug /unplug console -> no prob !

But: Boot with console attached and powered up -> disconnect after boot -> Panic !

There is an eeprom switch, that disables this behavior, but I do not rememeber it right now. Some setting deactivates the boot-device definition for the console.

If disabled, the (Serial) console can be diconnected like any other dumb terminal.

Volker

[Bill Hassell]

This is a very common problem for Sun servers but has no effect on HP-UX or any other boxes for that matter. Almost all modern console servers are advertised as "Sun-safe" for this reason.

Now as explained, there is nothing you can configure in the OS because the 'break' signal is not a character -- it is a special condition on the RS-232 line that can never occur during normal data transmissions. In the good old days, teletypewriters were connected using copper wire end-to-end and if the wire was broken, the machine would chatter indicating a break in the line. The break condition caused by the Lantronics box is doing exactly that and Sun hardware (*not* the OS) takes over and jumps into maintenance mode.

I would contact Lantronics for an upgrade as this condition is unaccpetable for any console server today.

[Matti_Kurkela]

I hate to contradict you Bill, but actually, on modern Solaris versions, this behaviour actually is configurable.

At least on Solaris 8 and above, there is a setting in /etc/default/kbd called KEYBOARD_ABORT. It is by default set to "enabled", but it can be set to "disabled". This will disable both Stop-A combination on Sun-native keyboards and the BREAK function on serial console.

It is also possible to set KEYBOARD_ABORT=alternate, which affects only serial console. Instead of BREAK, the abort will be a key sequence:
~

This is known as "Alternate Break sequence" and it can apparently be changed if the key sequence is not suitable.

See "man kbd" on Solaris platform for more info. It refers to other man pages concerning the Alternate Break sequence.

[Bill Hassell]

Thanks Matti. I work on Sun boxes only occasionally and many of them are fairly old, thus the reference. But it is still the reason that console concentrators have a Sun-safe reference. And I'll bet there are a few boxes out there that might change baud rates if they see a break coming in -- oh yeah, that would be HP-UX serial ports in association with gettydefs. The default entry for console entry in gettydefs doesn't switch but the 'general' gettydefs entry does indeed shift baud rates. (isn't it nice that general purpose serial ports are almost unused these days?)