SysRq behavior

SysRq behavior

[Frédéric L . W . Meunier]

I don't remember having the same problem months (6?) ago when
I built my first Kernel with this enabled (well, maybe I never
touched the key).

When built into the Kernel, by only pressing the
PrintScreen/SysRq the current application is terminated (tested
on a console and GNU screen). Is this just me or I should
expect it?

% calc
C-style arbitrary precision calculator (version 2.11.2t1.0)
Calc is open software. For license details type:  help
copyright
[Type "exit" to exit, or "help" for help.]

> zsh: quit

While running the application I press the key and you see the
result. It's very annoying because I accidentaly keep touching
it.

Kernel 2.2.17 on x86 (br-abnt2 keyboard, kbd 1.03). glibc 2.2,
but Kernel compiled with egcs 1.1.2.

The SysRq stuff works:

Dec  9 04:09:05 pervalidus kernel: SysRq: unRaw saK Boot Sync
Unmount showPc showTasks showMem loglevel0-8 tErm kIll killalL

-- 
0@pervalidus.{net,{dyndns.}org} TelFax: 55-21-717-2399 (Niterói-RJ BR)
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Re: SysRq behavior

[Pavel Machek]

Hi!

> I don't remember having the same problem months (6?) ago when
> I built my first Kernel with this enabled (well, maybe I never
> touched the key).
> 
> When built into the Kernel, by only pressing the
> PrintScreen/SysRq the current application is terminated (tested
> on a console and GNU screen). Is this just me or I should
> expect it?

Probably bug. Happens for me, too, and it is pretty nasty.

								Pavel
-- 
I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care."
Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org
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Re: SysRq behavior

[James Simmons]

> Hi!
> 
> > I don't remember having the same problem months (6?) ago when
> > I built my first Kernel with this enabled (well, maybe I never
> > touched the key).
> > 
> > When built into the Kernel, by only pressing the
> > PrintScreen/SysRq the current application is terminated (tested
> > on a console and GNU screen). Is this just me or I should
> > expect it?
> 
> Probably bug. Happens for me, too, and it is pretty nasty.

Just played with this bug. It doesn't kill a login shell but does any
app running on it. I just went looking for where "Quit" is printed
out. When I press SysRq Quit is printed on the command line. Any ideas?


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Re: SysRq behavior

[Alan Shutko]

James Simmons <jsimmons@suse.com> writes:

> Just played with this bug. It doesn't kill a login shell but does any
> app running on it. I just went looking for where "Quit" is printed
> out. When I press SysRq Quit is printed on the command line. Any ideas?

Not a bug.  Normally,. PrtSc will generate a ^\, which is the default
value of stty quit.  Try

stty quit ^A
cat

and hit PrtSc

-- 
Alan Shutko <ats@acm.org> - In a variety of flavors!
If you have to think twice about it, you're wrong.
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Re: SysRq behavior

[Pavel Machek]

Hi!

> > Just played with this bug. It doesn't kill a login shell but does any
> > app running on it. I just went looking for where "Quit" is printed
> > out. When I press SysRq Quit is printed on the command line. Any ideas?
> 
> Not a bug.  Normally,. PrtSc will generate a ^\, which is the default
> value of stty quit.  Try
> 
> stty quit ^A
> cat
> 
> and hit PrtSc

Okay, perhaps then it is bad for PrtSc to generate such dangerous
combination by default. Still bug ;-).
								Pavel
-- 
I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care."
Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org
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Re: SysRq behavior

[Tuomas Heino]

On Mon, 11 Dec 2000, James Simmons wrote:

> > > When built into the Kernel, by only pressing the
> > > PrintScreen/SysRq the current application is terminated (tested
> > > on a console and GNU screen). Is this just me or I should
> > > expect it?

Well this should happen even when sysrq is NOT compiled into the kernel...

> > Probably bug. Happens for me, too, and it is pretty nasty.

Not a bug - just an easy-to-disable "feature" - read on ;)

> Just played with this bug. It doesn't kill a login shell but does any
> app running on it. I just went looking for where "Quit" is printed
> out. When I press SysRq Quit is printed on the command line. Any ideas?

Well that "print-screen" key is usually bound to ^\ :

% dumpkeys | grep 'e  99'
keycode  99 = Control_backslash
        control alt     keycode  99 = Meta_Control_backslash

Now by default ^\ is bound to sigquit - and should be as quite a few
programs depend on that...

% dumpkeys | grep [^_]Control_backslash
keycode   5 = four             degree           dollar
Control_backslash Control_backslash
        altgr   control keycode  12 = Control_backslash
        control keycode  43 = Control_backslash
keycode  99 = Control_backslash

Looks like there're quite a few ways to generate ^\ - so disabling one of
them won't hurt:

% echo 'keycode  99 = VoidSymbol' | loadkeys

(Note that this leaves all the "modified" versions of sysrq to do whatever
they were already doing - so shift-printscreen will still generate ^\)

In any case putting that somewhere in your bootup scripts should solve it ;)

(or even users' login scripts as Linux allows anyone to screw up the
keyboard mappings - why?!)

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