alt+sysrq combinations on PE KVM switches

[Robert Wehner]

We have several Dell KVM console switches (Avocent re-brands, I
think), including the 2161DS and the 71PXP. The 1750, 2850, and 2950s
that we have attached to these KVMs are running RHEL4, Update 3. We
have enabled the "Magic SysRq" key, adding 'kernel.sysrq = 1' to
/etc/sysctl.conf and running 'sysctl –p'.

We just had a server "hang" and none of the SysRq key combinations
(alt+sysrq+m, alt+sysrq+w, and alt+sysrq+t) have caused the server to
display any data, or send any core file to our netdump server. I've
tested the same thing on a working system and had the same lack of
results.

These KVMs use the "prtscn/sysrq" key to pop up the menu to move
between servers. I'm wondering if there is some way that this is
interfering with the appropriate keystrokes getting to the actual
servers or something like that?  Dell support is investigating this
for me, but is not hopeful. They think the "prtscn/sysrq" is
hard-coded into the KVM and there isn't a way to re-map it elsewhere.

The KVMs use USB/PS2 ports to connect, not the serial port. Do the
SysRq functions work in non-serial console set-ups? Reading some of
the Google hits on this it seems that serial consoles are the norm for
using the Magic SysRq combinations.

I'd appreciate any help or experiences that anyone has to share. Thanks!

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Robert