How to enable CTRL+ALT+BACKSPACE

[Reindl Harald]

Am 07.07.2011 16:57, schrieb Daniele Guerrieri:
>> ok :-)
>>
>>> From wikipedia (probably also in kernel/Documentation but now i'm on
>>> a win machine) i've read:
>>
>> have you a link?
>> i do not find this on wikipedia
>> http://en.wikipedia.org/wiki/Sysrq
> 
> here the link: http://en.wikipedia.org/wiki/Magic_SysRq_key :)
> 
> this value is a "bitmask":
> 
>> i think this is not enough for "ALT+PRINT+K" because sync
>> is only for flushing disk-buffers, maybe i play around a
> hm, you're right, i think that, since it's a bitmask we need to sum
> the values we want: e.g. if we want
> sync (16),debugging(8), signalling(64), we have to sum
> -# value=8+16+64=88, which binary is: 01 01 10 00
> ---example:---------
> ______________
> 01: 00 00 00 01  |
> 02: 00 00 00 10  |
> 04: 00 00 01 00  |
> 08: 00 00 10 00  |
> 16: 00 01 00 00  |
> 32: 00 10 00 00  |
> 64: 01 00 00 00  |
> ______________|
>      01 01 10 00
> -------------------------
> So the magic number would be 88 :) this night i'll try it

i came to first to 84, with 88 CTRL+PRINT+K says in dmesg not allowed

with 84
 * CTRL+PRINT+S (sync buffers to disk) works
 * CTRL+PRINT+K (kill session and back to login) works
 * but REISUB kills processes (named, openvpn, vmware...)
 * After REISUB the system would with 84 in a bader state as reboot

finally i came to 20

 * CTRL+PRINT+S (sync buffers to disk) works
 * CTRL+PRINT+K (kill session and back to login) works
 * CTRL+PRINT+REISUB does nothing bad

th eonly strange gting is that ALT+F2 swicthes to terminal instead
open the xecute-dialog of KDE and after switch back to KDE the dialog
is still open - not sure what there happens but if this is only after
SYSRQ call which is not often used i think we can live with that
__________________

dmesg-output of REISUB:

Jul 16 13:56:34 srv-rhsoft kernel: SysRq : Keyboard mode set to system default
Jul 16 13:56:34 srv-rhsoft kernel: SysRq : This sysrq operation is disabled.
Jul 16 13:56:35 srv-rhsoft kernel: SysRq : This sysrq operation is disabled.
Jul 16 13:56:35 srv-rhsoft kernel: SysRq : Emergency Sync
Jul 16 13:56:35 srv-rhsoft kernel: Emergency Sync complete
Jul 16 13:56:36 srv-rhsoft kernel: SysRq : This sysrq operation is disabled.
Jul 16 13:56:36 srv-rhsoft kernel: SysRq : This sysrq operation is disabled.
___________________

http://www.mjmwired.net/kernel/Documentation/sysrq.txt

  2 - enable control of console logging level
  4 - enable control of keyboard (SAK, unraw)
  8 - enable debugging dumps of processes etc.
 16 - enable sync command
 32 - enable remount read-only
 64 - enable signalling of processes (term, kill, oom-kill)
128 - allow reboot/poweroff
256 - allow nicing of all RT tasks

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