Re: missing sysrq

Re: missing sysrq

[Dieter Nützel]

Am Freitag, 1. Juni 2001 16:51 schrieben Sie:
> > Have you tried "echo 1 > /proc/sys/kernel/sysrq"?
> > You need both, compiled in and activation.
>
> no, look at the code.  the enable variable defaults to 1.

Then there must be a bug?
I get "0" with 2.4.5-ac2 and -ac5 without "echo 1".

Fresh booted 2.4.5-ac2:

SunWave1>cat /proc/version
Linux version 2.4.5-ac2 (root@SunWave1) (gcc version 2.95.2 19991024 
(release)) #1 Mon May 28 05:42:09 CEST 2001
SunWave1>cat /proc/sys/kernel/sysrq
0

-Dieter

Re: missing sysrq

[george anzinger]

Dieter Nützel wrote:
> 
> Am Freitag, 1. Juni 2001 16:51 schrieben Sie:
> > > Have you tried "echo 1 > /proc/sys/kernel/sysrq"?
> > > You need both, compiled in and activation.
> >
> > no, look at the code.  the enable variable defaults to 1.
> 
> Then there must be a bug?
> I get "0" with 2.4.5-ac2 and -ac5 without "echo 1".
> 
> Fresh booted 2.4.5-ac2:

Bet not!  Most distro scripts turn it off on the way up.  Sometimes it
is a bit hard to find where they do it too.

George

Re: missing sysrq

[Dieter Nützel]

Am Samstag, 2. Juni 2001 00:31 schrieb george anzinger:
> Dieter Nützel wrote:
> > Am Freitag, 1. Juni 2001 16:51 schrieben Sie:
> > > > Have you tried "echo 1 > /proc/sys/kernel/sysrq"?
> > > > You need both, compiled in and activation.
> > >
> > > no, look at the code.  the enable variable defaults to 1.
> >
> > Then there must be a bug?
> > I get "0" with 2.4.5-ac2 and -ac5 without "echo 1".
> >
> > Fresh booted 2.4.5-ac2:
>
> Bet not!  Most distro scripts turn it off on the way up.  Sometimes it
> is a bit hard to find where they do it too.
>

Good point!

Easy for SuSE 7.1/7.2 (?).

SunWave1#grep SYSRQ /etc/rc.config
ENABLE_SYSRQ="no"

Thanks,
	Dieter

Re: missing sysrq

[H. Peter Anvin]

Followup to:  <20010601203841Z261493-933+3160@vger.kernel.org>
By author:    Dieter =?iso-8859-1?q?N=FCtzel?= <Dieter.Nuetzel@hamburg.de>
In newsgroup: linux.dev.kernel
>
> Am Freitag, 1. Juni 2001 16:51 schrieben Sie:
> > > Have you tried "echo 1 > /proc/sys/kernel/sysrq"?
> > > You need both, compiled in and activation.
> >
> > no, look at the code.  the enable variable defaults to 1.
> 
> Then there must be a bug?
> I get "0" with 2.4.5-ac2 and -ac5 without "echo 1".
> 
> Fresh booted 2.4.5-ac2:
> 
> SunWave1>cat /proc/version
> Linux version 2.4.5-ac2 (root@SunWave1) (gcc version 2.95.2 19991024 
> (release)) #1 Mon May 28 05:42:09 CEST 2001
> SunWave1>cat /proc/sys/kernel/sysrq
> 0
> 

Let me guess... you're using a RedHat system?  RedHat, for some
idiotic reason, defaults to actively turning this off for you (and
they turn Stop-A off on SPARC, too.)

	-hpa
-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt

Re: missing sysrq

[Alan Cox]

> Let me guess... you're using a RedHat system?  RedHat, for some
> idiotic reason, defaults to actively turning this off for you (and
> they turn Stop-A off on SPARC, too.)
> 

We turn it off by default because its a rather large dangerous security
hole to leave around when a naiive user makes a basic installation. It is much
better that it is enabled by someone who knows what they are doing and makes
the decision to do so. Thats why we contributed the patch to make syrq runtime
configurable

Tools like powertweak even give you a nice gui interface for managing it.

Re: missing sysrq

[H. Peter Anvin]

Alan Cox wrote:
> 
> > Let me guess... you're using a RedHat system?  RedHat, for some
> > idiotic reason, defaults to actively turning this off for you (and
> > they turn Stop-A off on SPARC, too.)
> >
> 
> We turn it off by default because its a rather large dangerous security
> hole to leave around when a naiive user makes a basic installation. It is much
> better that it is enabled by someone who knows what they are doing and makes
> the decision to do so. Thats why we contributed the patch to make syrq runtime
> configurable
> 
> Tools like powertweak even give you a nice gui interface for managing it.

Sure, if you know about it and know how to find it!

	-hpa

Re: missing sysrq

[Russell King]

On Fri, Jun 01, 2001 at 04:13:02PM -0700, H. Peter Anvin wrote:
> Let me guess... you're using a RedHat system?  RedHat, for some
> idiotic reason, defaults to actively turning this off for you (and
> they turn Stop-A off on SPARC, too.)

Umm, its off by default in 2.4.5 kernels, unless altered by a
distributions boot scripts.

--
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html

Re: missing sysrq

[H. Peter Anvin]

Russell King wrote:
> 
> On Fri, Jun 01, 2001 at 04:13:02PM -0700, H. Peter Anvin wrote:
> > Let me guess... you're using a RedHat system?  RedHat, for some
> > idiotic reason, defaults to actively turning this off for you (and
> > they turn Stop-A off on SPARC, too.)
> 
> Umm, its off by default in 2.4.5 kernels, unless altered by a
> distributions boot scripts.
> 

That seems like a very bad idea.  What if there is a boot script bug?

	-hpa

Re: missing sysrq

[Russell King]

On Sat, Jun 02, 2001 at 03:10:55PM -0700, H. Peter Anvin wrote:
> That seems like a very bad idea.  What if there is a boot script bug?

Also think about kernel panics - the only thing that works after that
is the power or (if you have it connected) reset button.  ctrl-alt-del
needs keventd to work, and since sysrq-b is disabled by default...

However, IMHO that is a non-point because you need to be physically
at the system either way to solve the problem.

--
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html

Re: missing sysrq

[H. Peter Anvin]

Russell King wrote:
> 
> On Sat, Jun 02, 2001 at 03:10:55PM -0700, H. Peter Anvin wrote:
> > That seems like a very bad idea.  What if there is a boot script bug?
> 
> Also think about kernel panics - the only thing that works after that
> is the power or (if you have it connected) reset button.  ctrl-alt-del
> needs keventd to work, and since sysrq-b is disabled by default...
> 
> However, IMHO that is a non-point because you need to be physically
> at the system either way to solve the problem.
> 

Not true if you have a serial console (and SysRq over serial console
happens to work correctly that day.)  Assuming this change is corrected
to be sane.

	-hpa

Re: missing sysrq

[D. Stimits]

Dieter Nützel wrote:
> 
> > D. Stimits wrote:
> >
> > > Bernd Eckenfels wrote:
> > > >
> > > In article <3B15EF16.89B18D@idcomm.com> you wrote:
> > > > However, if I go to /proc/sys/kernel/sysrq does not exist.
> > >
> > > It is a compile time option, so the person who compiled your kernel
> > > left it out.
> >
> > I compiled it, and the sysrq is definitely in the config. No doubt at
> > all. I also use make mrproper and config again before dep and actual
> > compile. Maybe it is just a quirk/oddball.
> >
> > D. Stimits, stimits@idcomm.com
> 
> Have you tried "echo 1 > /proc/sys/kernel/sysrq"?
> You need both, compiled in and activation.

It is compiled in, but the echo is summarily rejected. Root is not
allowed to write to that file, which doesn't exist. I'm going to just
wipe out everything from that kernel and redo the whole thing.

D. Stimits, stimits@idcomm.com

> 
> Regards,
>         Dieter
> --
> Dieter Nützel
> Graduate Student, Computer Science
> 
> email: nuetzel@kogs.informatik.uni-hamburg.de
> @home: Dieter.Nuetzel@hamburg.de

Re: missing sysrq

[Dieter Nützel]

> D. Stimits wrote:
>
> > Bernd Eckenfels wrote:
> > > 
> > In article <3B15EF16.89B18D@idcomm.com> you wrote:
> > > However, if I go to /proc/sys/kernel/sysrq does not exist.
> > 
> > It is a compile time option, so the person who compiled your kernel
> > left it out.
>
> I compiled it, and the sysrq is definitely in the config. No doubt at
> all. I also use make mrproper and config again before dep and actual
> compile. Maybe it is just a quirk/oddball.
>
> D. Stimits, stimits@idcomm.com

Have you tried "echo 1 > /proc/sys/kernel/sysrq"?
You need both, compiled in and activation.

Regards,
	Dieter
-- 
Dieter Nützel
Graduate Student, Computer Science

email: nuetzel@kogs.informatik.uni-hamburg.de
@home: Dieter.Nuetzel@hamburg.de

Re: missing sysrq

[Mike A. Harris]

On Fri, 1 Jun 2001, Dieter Nützel wrote:

>> > In article <3B15EF16.89B18D@idcomm.com> you wrote:
>> > > However, if I go to /proc/sys/kernel/sysrq does not exist.
>> >
>> > It is a compile time option, so the person who compiled your kernel
>> > left it out.
>>
>> I compiled it, and the sysrq is definitely in the config. No doubt at
>> all. I also use make mrproper and config again before dep and actual
>> compile. Maybe it is just a quirk/oddball.
>>
>> D. Stimits, stimits@idcomm.com
>
>Have you tried "echo 1 > /proc/sys/kernel/sysrq"?
>You need both, compiled in and activation.

If you *know* it is compiled into your kernel, and you *know* it
is enabled via the above, and it still does not work, do the
following:

Run:

showkey -s

Then press LALT quickly followed by SYSRQ, and keep holding both
down, and you should see:

0x38
0x54

You might see a bunch of extra 0x38's which is ok.

If however when you press ALT-SYSRQ you see:

0x38 0x54 0xd4

and are still holding both keys down, then your keyboard is
broken and incompatible with the kernel SYSRQ feature.

A proper keyboard will only show "0x38 0x54".  I have written a
patch for SYSRQ to allow it to be used with broken keyboards that
send the make+break code for the SYSRQ sequence simultaneously.

If you need it, let me know and I'll send it to you.



----------------------------------------------------------------------
    Mike A. Harris  -  Linux advocate  -  Open Source advocate
       Opinions and viewpoints expressed are solely my own.
----------------------------------------------------------------------

Re: missing sysrq

[D. Stimits]

"Mike A. Harris" wrote:
> 
> On Fri, 1 Jun 2001, Dieter Nützel wrote:
> 
> >> > In article <3B15EF16.89B18D@idcomm.com> you wrote:
> >> > > However, if I go to /proc/sys/kernel/sysrq does not exist.
> >> >
> >> > It is a compile time option, so the person who compiled your kernel
> >> > left it out.
> >>
> >> I compiled it, and the sysrq is definitely in the config. No doubt at
> >> all. I also use make mrproper and config again before dep and actual
> >> compile. Maybe it is just a quirk/oddball.
> >>
> >> D. Stimits, stimits@idcomm.com
> >
> >Have you tried "echo 1 > /proc/sys/kernel/sysrq"?
> >You need both, compiled in and activation.

Since then I've completely removed that kernel source and kernel, only
the config file remains (and it had it activated if the config followed
it). All kernels before worked, and those since then also work, so I
know it isn't the keyboard. I also always run make mrproper and config
it again between compiles (I keep a list of config history), so I don't
know what was wrong, but replacing the kernel fixed it, and is no longer
an issue. I will, however, keep the showkey suggestion handy in case it
ever does it again.

D. Stimits, stimits@idcomm.com

> 
> If you *know* it is compiled into your kernel, and you *know* it
> is enabled via the above, and it still does not work, do the
> following:
> 
> Run:
> 
> showkey -s
> 
> Then press LALT quickly followed by SYSRQ, and keep holding both
> down, and you should see:
> 
> 0x38
> 0x54
> 
> You might see a bunch of extra 0x38's which is ok.
> 
> If however when you press ALT-SYSRQ you see:
> 
> 0x38 0x54 0xd4
> 
> and are still holding both keys down, then your keyboard is
> broken and incompatible with the kernel SYSRQ feature.
> 
> A proper keyboard will only show "0x38 0x54".  I have written a
> patch for SYSRQ to allow it to be used with broken keyboards that
> send the make+break code for the SYSRQ sequence simultaneously.
> 
> If you need it, let me know and I'll send it to you.
> 
> ----------------------------------------------------------------------
>     Mike A. Harris  -  Linux advocate  -  Open Source advocate
>        Opinions and viewpoints expressed are solely my own.
> ----------------------------------------------------------------------

Re: missing sysrq

[David Ford]

BTW, you ONLY need to echo 1 > /proc../sysrq if you use a distribution 
that puts a 0 there on init.

By default the kernel initializes with '1'.

David

>>>I compiled it, and the sysrq is definitely in the config. No doubt at
>>>all. I also use make mrproper and config again before dep and actual
>>>compile. Maybe it is just a quirk/oddball.
>>>
>>>D. Stimits, stimits@idcomm.com
>>>
>>Have you tried "echo 1 > /proc/sys/kernel/sysrq"?
>>You need both, compiled in and activation.
>>

missing sysrq

[D. Stimits]

I have compiled the magic sysrq as enabled in most kernels I've used for
quite a while. Most recently 2.4.5-ac5, on a RH 7.1 SMP machine with
APIC disabled. The /etc/sysctl.conf contains this line:
kernel.sysrq = 1

However, if I go to /proc/sys/kernel/sysrq does not exist. Nor is it
possible for root to echo to that file name. Attempts to use the magic
sysrq keys, such as for sync, prove that it truly is not enabled, or is
otherwise missing. Has something changed in the enabling of magic sysrq?
Or is this one of those strange "it should be there" things?

A second observation, maybe related (maybe not), is the
/var/log/messages line:
sysctl: error: permission denied on key 'vm.freepages'

This particular line has occurred since install of RH 7.1, even with its
original kernel, but continues into 2.4.5-ac5. The relevant line in
/etc/sysctl.conf:
vm.freepages = 383 766 1149

This line is how the original RH 7.1 install set it up. This particular
machine has 256 MB of ram, and somewhat over a 1 GB of swap. Is the
vm.freepages not intended to be set in /etc/sysctl.conf? Or maybe the
specs are off for this particular hardware? I know a lot of vm changes
are going on in the kernel, and wondering if this could be something
that used to be supported but no longer is.

D. Stimits, stimits@idcomm.com

Re: missing sysrq

[Bernd Eckenfels]

In article <3B15EF16.89B18D@idcomm.com> you wrote:
> However, if I go to /proc/sys/kernel/sysrq does not exist.

It is a compile time option, so the person who compiled your kernel left it
out.

> vm.freepages = 383 766 1149

tat feature is removed in recent VM Systems.

Greetings
Bernd

Re: missing sysrq

[D. Stimits]

Bernd Eckenfels wrote:
> 
> In article <3B15EF16.89B18D@idcomm.com> you wrote:
> > However, if I go to /proc/sys/kernel/sysrq does not exist.
> 
> It is a compile time option, so the person who compiled your kernel left it
> out.

I compiled it, and the sysrq is definitely in the config. No doubt at
all. I also use make mrproper and config again before dep and actual
compile. Maybe it is just a quirk/oddball.

D. Stimits, stimits@idcomm.com

> 
> > vm.freepages = 383 766 1149
> 
> tat feature is removed in recent VM Systems.
> 
> Greetings
> Bernd
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Re: missing sysrq

[Mike A. Harris]

On Thu, 31 May 2001, D. Stimits wrote:

>Date: Thu, 31 May 2001 17:48:34 -0600
>From: D. Stimits <stimits@idcomm.com>
>To: unlisted-recipients:;;@timpanogas.com (no To-header on input)
>Cc: linux-kernel@vger.kernel.org
>Content-Type: text/plain; charset=us-ascii
>Subject: Re: missing sysrq
>
>Bernd Eckenfels wrote:
>>
>> In article <3B15EF16.89B18D@idcomm.com> you wrote:
>> > However, if I go to /proc/sys/kernel/sysrq does not exist.
>>
>> It is a compile time option, so the person who compiled your kernel left it
>> out.
>
>I compiled it, and the sysrq is definitely in the config. No doubt at
>all. I also use make mrproper and config again before dep and actual
>compile. Maybe it is just a quirk/oddball.

What does this say:

ksyms -a |grep -i sysrq


----------------------------------------------------------------------
    Mike A. Harris  -  Linux advocate  -  Open Source advocate
       Opinions and viewpoints expressed are solely my own.
----------------------------------------------------------------------
Who knows what dangerous code lurks in the hearts of men?
Only the Shadowman(TM) knows...  Mike A. Harris <mharris@redhat.com>