help: sysrq and X

help: sysrq and X

[Eyal Lebedinsky]

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?

Thanks

-- 
Eyal Lebedinsky (eyal@eyal.emu.id.au) <http://samba.org/eyal/>

Re: help: sysrq and X

[Andrew Morton]

Eyal Lebedinsky <eyal@eyal.emu.id.au> 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.

Re: help: sysrq and X

[Dmitry Torokhov]

On Sunday 21 November 2004 06:21 pm, Eyal Lebedinsky 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?
> 

Try use SysRQ+K (SAK) - 95% when my X server locks up I can use SAK and then
killall -9 X and everythig is fine.  

-- 
Dmitry