Maxime Haselbauer posted on Thu, 15 May 2014 22:16:48 +0200 as excerpted:
> I am using kde since 2010 There has been continuously a problem with a
> given component of KDE that I won't even mentionn it but basically the
> problem is like that:
> 1)you work 2)and suddenly a programm starts to rev-up at 100% cpu and
> your computer does not respond anymore until you press the shutdown
> button
>
> My questions:
> 1) Is it currently possible to have like an "emegency" button so that
> when this happen you would press on it, it would freeze everything and
> head you back to a terminal immediatly where you can kill those mother
> fuckers Basically it would be like ctrl+alt+f1 but ctrl+alt+f1 does not
> respond as well when something is running at 100% cpu...
First, please tone down your language a bit. It's quite possible there
are kids or other sensitive folks subscribed, and it's also quite
possible to express frustration using the traditional YELLING and
*YELLING* *EVEN* *LOUDER* methods without such language. Or if you
/really/ feel the need, use "comic swearing": *#@#_%. It gets the
message across. =8^0
Meanwhile...
As vgobbo says, try the "magic sys-request" sequences. But here's a bit
more detail and additional sequence suggestions:
Wikipedia on SysRQ: https://en.wikipedia.org/wiki/System_request
Quote of interest:
>> On the later [x86] 101-key keyboard, it shares a physical key with the
>> Print Screen key function. One must hold down the Alt key while
>> pressing this “dual-function” key to invoke SysRq.
Thus the alt-srq sequence. To that, a third key is added, depending on
the desired action.
Wikipedia on the Linux-specific ' "Magic SysRq key":
https://en.wikipedia.org/wiki/Magic_SysRq_key
The kernel's own magic-srq document can be found at
$KERNDIR/Documentation/sysrq.txt (where $KERNDIR is /usr/src/linux or
wherever else you or your distro places your kernel sources directory).
Assuming magic-srq is enabled (or enable-able) on your distro, the most
common use, as the above page explains, is REISUB (assuming QWERTY
keyboard layout, there's a table on the wiki page for other common
layouts), to effect a safer emergency reboot, when nothing else seems to
work. Additionally, how far you have to go in that sequence before you
get any indication that it's helping is a good indication of how horribly
locked up the system actually was/is. If the RE gets a response, it
wasn't too bad. OTOH, if you get all the way to the B before anything
(including drive activity indication) happens, the kernel was corrupted
badly enough that it feared it couldn't safely even write to storage to
sync and remount-read-only, which means things were pretty bad, and if
even the B doesn't respond, then the kernel itself was locked up, to the
point it couldn't even see or process the unconditional reboot directive.
REISUB:
unRaw - Turn off X's raw keyboard mode
tErm- Terminate all processes that will terminate gracefully
kIll- Force-kill all remaining processes
Sync- Flush all unwritten data to storage (disk/SSD)
remoUnt - Remount all filesystems read-only
reBoot - Unconditional immediate reboot
Note that unlike the other keys in the REISUB sequence, alt-srq-s (sync)
by itself is generally safe at any time and can be used to force-flush
unwritten data to disk before an operation you think might crash the
computer. You can then continue as if nothing happened, and/or
repeatedly hit alt-srq-s in ordered to repeatedly sync an ongoing
operation. I use it that way myself from time to time.
Meanwhile, of particular interest for this thread is another magic-srq
key, the K/saK/Secure-access-key, alt-srq-k. This key kills any process
listening on the current virtual terminal along with all its children.
As a result, it can be used to force-kill an unresponsive X, if
necessary. It may or may not return you to a shell prompt (tho if it
doesn't, sometimes using the alt-srq-r/unraw, followed by the usual ctrl-
alt-Fn sequence, to switch to a different VT, can sometimes help).
This is what I might well try if I found myself in the situation you
describe, since 100% CPU will very likely still respond to magic-srq, and
the alt-srq-k combo has a good chance of killing X and either letting it
respawn (if you use a *DM graphical login) or getting you back a text
login (if as me you login at a text terminal and run startx to start kde).
The above references should get you started if you're interested in more,
and of course a google on "magic sysrequest" and variants should turn up
a wealth of community commentary as well.
--
Duncan - List replies preferred. No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master." Richard Stallman
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