Re: help: sysrq and X

[Andrew Morton]

Eyal Lebedinsky <eyal@xxxxxxxxxxxxxx> wrote:
>
> I am trying to diagnose a hard lockup. The only way I can reproduce it is
>  with mythtv. When the system locks up (no mouse, no activity in X, no message
>  logged) I can use magic sysrq, but I cannot see the output.
> 
>  Using 'r' does not enable console switching. However 'b' will boot the
>  system, and I hope 's' and 'u' did something blindly.
> 
>  I there a way to regain a text console in order to inspect the kernel?
> 
>  I can connect a machine to the serial port if this will help - does
>  sysrq work though the serial port? Which software should I use on
>  the serial port (on the 'other' machine) for this purpose then?

Yes, serial console is the best way to do this.  Add `console=ttyS0' to the
kernel boot command line and use `<break>t' to get an all-task backtrace.

If you're using minicom (spit) on the other end, Control-A F t is the
combination to use.

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