It is hard to know where to start with the problems with the use of the SysReg key.. Since acording to the Wikipedia notes in order to get these Magic SysReg features to work you have tp add the Ctrl button. So to reboot you would have to use the Ctrl+Alt+SysReg+ b button. On my workstation Keyboard this is nearly impossible to do because of the position of the SysReg key in the upper right corner of the keyboard. On my laptop where I can hit the keys the function fails to work. Without the Ctrl all you get is screen shots which I do get.
With the alternate approach of: echo key > /proc/sysreq-trigger the reboot works but I can't detect anything else working.
So how does one use these magic keys ?
On 20 August 2012 23:55, Aaron Konstam akonstam@sbcglobal.net wrote:
It is hard to know where to start with the problems with the use of the
<--SNIP-->
So how does one use these magic keys ?
Could you please post the link to the wikipedia?
On 08/20/2012 12:55 PM, Aaron Konstam wrote:
It is hard to know where to start with the problems with the use of the SysReg key.. Since acording to the Wikipedia notes in order to get these Magic SysReg features to work you have tp add the Ctrl button. So to reboot you would have to use the Ctrl+Alt+SysReg+ b button. On my workstation Keyboard this is nearly impossible to do because of the position of the SysReg key in the upper right corner of the keyboard. On my laptop where I can hit the keys the function fails to work. Without the Ctrl all you get is screen shots which I do get.
With the alternate approach of: echo key > /proc/sysreq-trigger the reboot works but I can't detect anything else working.
So how does one use these magic keys ?
I can't speak for anybody else, but when I've experimented with it, I used both hands.
On 08/20/2012 12:55 PM, Aaron Konstam wrote:
It is hard to know where to start with the problems with the use of the SysReg key.. Since acording to the Wikipedia notes in order to get these Magic SysReg features to work you have tp add the Ctrl button. So to reboot you would have to use the Ctrl+Alt+SysReg+ b button. On my workstation Keyboard this is nearly impossible to do because of the position of the SysReg key in the upper right corner of the keyboard. On my laptop where I can hit the keys the function fails to work. Without the Ctrl all you get is screen shots which I do get.
With the alternate approach of: echo key > /proc/sysreq-trigger the reboot works but I can't detect anything else working.
So how does one use these magic keys ?
You have to enable the sysrq key in /etc/sysctl.conf: kernel.sysrq = 1
In non-graphical mode it's just Alt+SysRq (not Ctrl, and not Alt+Ctrl), but the GUI can choose to ignore the combination - there used to be some X keyboard setting you could set globally, but it doesn't work anymore. I think there's some workaround for gnome, but I never did figure out how to make it work right in XFCE.
Lastly, on the laptop the SysRq key might only be usable with Fn modifier (Ctrl+Alt+Fn+SysRq+...), though Alt+PrintScreen has worked for me on all laptops I've tried (in text mode)
On Tue, 2012-08-21 at 00:00 +0400, Hiisi wrote:
On 20 August 2012 23:55, Aaron Konstam akonstam@sbcglobal.net wrote:
It is hard to know where to start with the problems with the use of the
<--SNIP-->
So how does one use these magic keys ?
Could you please post the link to the wikipedia?
Hiisi. Registered Linux User #487982. Be counted at: http://counter.li.org/ -- Spandex is a privilege, not a right.
link Is: http://en.wikipedia.org/wiki/Magic_SysRq_key
On 08/20/2012 01:05 PM, Joe Zeff uttered this comment:
On 08/20/2012 12:55 PM, Aaron Konstam wrote:
It is hard to know where to start with the problems with the use of the SysReg key.. Since acording to the Wikipedia notes in order to get these Magic SysReg features to work you have tp add the Ctrl button. So to reboot you would have to use the Ctrl+Alt+SysReg+ b button. On my workstation Keyboard this is nearly impossible to do because of the position of the SysReg key in the upper right corner of the keyboard. On my laptop where I can hit the keys the function fails to work. Without the Ctrl all you get is screen shots which I do get.
With the alternate approach of: echo key > /proc/sysreq-trigger the reboot works but I can't detect anything else working.
So how does one use these magic keys ?
I can't speak for anybody else, but when I've experimented with it, I used both hands.
It's supposed to be a simultaneous press of ALT, SYSRQ (or PRINTSCREEN) and the command key (B in your case). Note it only works if /proc/sys/kernel/sysrq contains a non-zero value. To enable ALL functionality, first set /proc/sys/kernel/sysrq to the value "1":
echo "1" >/proc/sys/kernel/sysrq
Then hit your key combo. Some keyboards may have issues with so many simultaneous keypresses. In those cases hold down ALT, then press and release SYSRQ, then press and release your command key and finally release ALT.
It's been a while since I futzed with it. If you have the kernel-doc RPM installed, it's explained in
/usr/share/doc/kernel-doc-(version)/Documentation/sysrq.txt
Your mileage may vary. Batteries not included. Void where prohibited. ---------------------------------------------------------------------- - Rick Stevens, Systems Engineer, AllDigital ricks@alldigital.com - - AIM/Skype: therps2 ICQ: 22643734 Yahoo: origrps2 - - - - When in doubt, mumble. - ----------------------------------------------------------------------
On Mon, 2012-08-20 at 13:05 -0700, Joe Zeff wrote:
On 08/20/2012 12:55 PM, Aaron Konstam wrote:
It is hard to know where to start with the problems with the use of the SysReg key.. Since acording to the Wikipedia notes in order to get these Magic SysReg features to work you have tp add the Ctrl button. So to reboot you would have to use the Ctrl+Alt+SysReg+ b button. On my workstation Keyboard this is nearly impossible to do because of the position of the SysReg key in the upper right corner of the keyboard. On my laptop where I can hit the keys the function fails to work. Without the Ctrl all you get is screen shots which I do get.
With the alternate approach of: echo key > /proc/sysreq-trigger the reboot works but I can't detect anything else working.
So how does one use these magic keys ?
I can't speak for anybody else, but when I've experimented with it, I used both hands.
Ok, it can be reached when you use both hands but it still does not work for me. Does it matter which Ctrl key you use?
Just to be clear, in /etc/sysctl.conf I changed: kernel.sysrq to 1 from 0.
On 08/20/2012 01:12 PM, Konstantin Svist wrote:
In non-graphical mode it's just Alt+SysRq (not Ctrl, and not Alt+Ctrl), but the GUI can choose to ignore the combination - there used to be some X keyboard setting you could set globally, but it doesn't work anymore. I think there's some workaround for gnome, but I never did figure out how to make it work right in XFCE.
I've found on my desktop that if I'm at an alternate terminal, without the GUI being active, I can usually get it to work if I use the right Alt key, but not the left; if start with the Control key, however, it works just fine with either Alt key. So far, I've not tried it on my laptop.
On 08/20/2012 01:24 PM, Aaron Konstam uttered this comment:
On Mon, 2012-08-20 at 13:05 -0700, Joe Zeff wrote:
On 08/20/2012 12:55 PM, Aaron Konstam wrote:
It is hard to know where to start with the problems with the use of the SysReg key.. Since acording to the Wikipedia notes in order to get these Magic SysReg features to work you have tp add the Ctrl button. So to reboot you would have to use the Ctrl+Alt+SysReg+ b button. On my workstation Keyboard this is nearly impossible to do because of the position of the SysReg key in the upper right corner of the keyboard. On my laptop where I can hit the keys the function fails to work. Without the Ctrl all you get is screen shots which I do get.
With the alternate approach of: echo key > /proc/sysreq-trigger the reboot works but I can't detect anything else working.
So how does one use these magic keys ?
I can't speak for anybody else, but when I've experimented with it, I used both hands.
Ok, it can be reached when you use both hands but it still does not work for me. Does it matter which Ctrl key you use?
It shouldn't, but it's not "CTRL", it's "ALT". ALT-SYSRQ-commandkey
Just to be clear, in /etc/sysctl.conf I changed: kernel.sysrq to 1 from 0.
Did you "sysctl -p" or reboot after doing that? ---------------------------------------------------------------------- - Rick Stevens, Systems Engineer, AllDigital ricks@alldigital.com - - AIM/Skype: therps2 ICQ: 22643734 Yahoo: origrps2 - - - - Physics is like sex ... it may give some practical results, but - - that's not why we do it. -- Richard Feynman ----------------------------------------------------------------------
On 20 August 2012 21:24, Aaron Konstam akonstam@sbcglobal.net wrote:
I can't speak for anybody else, but when I've experimented with it, I used both hands.
Ok, it can be reached when you use both hands but it still does not work for me. Does it matter which Ctrl key you use?
Offtopic: Almost 20 years ago one of my friends used to teach computing to 10 year olds (DOS days). When he was trying to teach how to do CTRL-ALT-DEL, he fell off laughing when one of his students held CTRL using one finger on one hand, ALT using an other finger on the other hand and then hit the ALT using his nose...
Try that method in doubt. :)
(Hint, if it's a laptop, you might have to use the so-called function key)
On 20 August 2012 21:29, Hakan Koseoglu hakan@koseoglu.org wrote:
to do CTRL-ALT-DEL, he fell off laughing when one of his students held CTRL using one finger on one hand, ALT using an other finger on the other hand and then hit the ALT using his nose...
Of course, that should have been, CTRL, DEL and ALT in that order. Idiot me. :) Can't even tell a story straight.
On Mon, 2012-08-20 at 13:26 -0700, Rick Stevens wrote:
On 08/20/2012 01:24 PM, Aaron Konstam uttered this comment:
On Mon, 2012-08-20 at 13:05 -0700, Joe Zeff wrote:
On 08/20/2012 12:55 PM, Aaron Konstam wrote:
It is hard to know where to start with the problems with the use of the SysReg key.. Since acording to the Wikipedia notes in order to get these Magic SysReg features to work you have tp add the Ctrl button. So to reboot you would have to use the Ctrl+Alt+SysReg+ b button. On my workstation Keyboard this is nearly impossible to do because of the position of the SysReg key in the upper right corner of the keyboard. On my laptop where I can hit the keys the function fails to work. Without the Ctrl all you get is screen shots which I do get.
With the alternate approach of: echo key > /proc/sysreq-trigger the reboot works but I can't detect anything else working.
So how does one use these magic keys ?
I can't speak for anybody else, but when I've experimented with it, I used both hands.
Ok, it can be reached when you use both hands but it still does not work for me. Does it matter which Ctrl key you use?
It shouldn't, but it's not "CTRL", it's "ALT". ALT-SYSRQ-commandkey
Just to be clear, in /etc/sysctl.conf I changed: kernel.sysrq to 1 from 0.
Did you "sysctl -p" or reboot after doing that?
yes I did.
On 08/20/2012 01:20 PM, Rick Stevens wrote:
It's supposed to be a simultaneous press of ALT, SYSRQ (or PRINTSCREEN) and the command key (B in your case).
I've had good results from pressing the keys sequentially, but not releasing any of them until they're all pressed. YMMV, of course, but it's worth a try.
On 08/20/2012 01:24 PM, Aaron Konstam wrote:
Ok, it can be reached when you use both hands but it still does not work for me. Does it matter which Ctrl key you use?
I've always used the left one.
Just to be clear, in /etc/sysctl.conf I changed: kernel.sysrq to 1 from 0.
If you've rebooted since doing that, you've turned it off.
On Mon, 2012-08-20 at 13:20 -0700, Rick Stevens wrote:
On 08/20/2012 01:05 PM, Joe Zeff uttered this comment:
On 08/20/2012 12:55 PM, Aaron Konstam wrote:
It is hard to know where to start with the problems with the use of the SysReg key.. Since acording to the Wikipedia notes in order to get these Magic SysReg features to work you have tp add the Ctrl button. So to reboot you would have to use the Ctrl+Alt+SysReg+ b button. On my workstation Keyboard this is nearly impossible to do because of the position of the SysReg key in the upper right corner of the keyboard. On my laptop where I can hit the keys the function fails to work. Without the Ctrl all you get is screen shots which I do get.
With the alternate approach of: echo key > /proc/sysreq-trigger the reboot works but I can't detect anything else working.
So how does one use these magic keys ?
I can't speak for anybody else, but when I've experimented with it, I used both hands.
It's supposed to be a simultaneous press of ALT, SYSRQ (or PRINTSCREEN) and the command key (B in your case). Note it only works if /proc/sys/kernel/sysrq contains a non-zero value. To enable ALL functionality, first set /proc/sys/kernel/sysrq to the value "1":
echo "1" >/proc/sys/kernel/sysrq
Then hit your key combo. Some keyboards may have issues with so many simultaneous keypresses. In those cases hold down ALT, then press and release SYSRQ, then press and release your command key and finally release ALT.
It's been a while since I futzed with it. If you have the kernel-doc RPM installed, it's explained in
/usr/share/doc/kernel-doc-(version)/Documentation/sysrq.txt
I appreciate all these tips but none make the sysrq suctions work. I'll just give up.
-
On 08/20/2012 02:27 PM, Aaron Konstam uttered this comment:
On Mon, 2012-08-20 at 13:20 -0700, Rick Stevens wrote:
On 08/20/2012 01:05 PM, Joe Zeff uttered this comment:
On 08/20/2012 12:55 PM, Aaron Konstam wrote:
It is hard to know where to start with the problems with the use of the SysReg key.. Since acording to the Wikipedia notes in order to get these Magic SysReg features to work you have tp add the Ctrl button. So to reboot you would have to use the Ctrl+Alt+SysReg+ b button. On my workstation Keyboard this is nearly impossible to do because of the position of the SysReg key in the upper right corner of the keyboard. On my laptop where I can hit the keys the function fails to work. Without the Ctrl all you get is screen shots which I do get.
With the alternate approach of: echo key > /proc/sysreq-trigger the reboot works but I can't detect anything else working.
So how does one use these magic keys ?
I can't speak for anybody else, but when I've experimented with it, I used both hands.
It's supposed to be a simultaneous press of ALT, SYSRQ (or PRINTSCREEN) and the command key (B in your case). Note it only works if /proc/sys/kernel/sysrq contains a non-zero value. To enable ALL functionality, first set /proc/sys/kernel/sysrq to the value "1":
echo "1" >/proc/sys/kernel/sysrq
Then hit your key combo. Some keyboards may have issues with so many simultaneous keypresses. In those cases hold down ALT, then press and release SYSRQ, then press and release your command key and finally release ALT.
It's been a while since I futzed with it. If you have the kernel-doc RPM installed, it's explained in
/usr/share/doc/kernel-doc-(version)/Documentation/sysrq.txt
I appreciate all these tips but none make the sysrq suctions work. I'll just give up.
Worked for me on my Dell laptop. Process:
1. Did 'echo "1" >/proc/sys/kernel/sysrq' 2. Held down left-ALT, held down PRNTSCR, pressed "h" 3. Released all three keys 4. Ran "dmesg" and saw this:
[111065.967134] SysRq : HELP : loglevel(0-9) reBoot Crash terminate-all-tasks(E) memory-full-oom-kill(F) kill-all-tasks(I) thaw-filesystems(J) saK show-backtrace-all-active-cpus(L) show-memory-usage(M) nice-all-RT-tasks(N) powerOff show-registers(P) show-all-timers(Q) unRaw Sync show-task-states(T) Unmount force-fb(V) show-blocked-tasks(W) dump-ftrace-buffer(Z)
5. Did 'echo "0" >/proc/sys/kernel/sysrq' to disable SYSRQ.
Fully updated F17, 3.5.2-1.fc17.x86_64, XFCE and xfwm4 window manager. ---------------------------------------------------------------------- - Rick Stevens, Systems Engineer, AllDigital ricks@alldigital.com - - AIM/Skype: therps2 ICQ: 22643734 Yahoo: origrps2 - - - - To err is human. To forgive, a large sum of money is needed. - ----------------------------------------------------------------------
On 21.08.2012, Aaron Konstam wrote:
/usr/share/doc/kernel-doc-(version)/Documentation/sysrq.txt
I appreciate all these tips but none make the sysrq suctions work. I'll just give up.
1. Look into your kernel .config if m-sysrq is in your kernel: CONFIG_MAGIC_SYSRQ=y
Standard Fedora kernels have it compiled in, but it is disabled by default.
2. Set "kernel.sysrq = 1" in /etc/sysctl.conf and do a "sysctl -p".
3. Now press the right ALT key together with PrtScrn, keep holding this combination and press e.g. "s". Now you should see this in /var/log/messages:
Aug 21 07:53:07 wildsau kernel: [ 1541.017462] SysRq : Emergency Sync Aug 21 07:53:07 wildsau kernel: [ 1541.017702] Emergency Sync complete
On Tue, 2012-08-21 at 07:55 +0200, Heinz Diehl wrote:
Now press the right ALT key together with PrtScrn...
With qualifier keys, such as CTRL, SHIFT, ALT, which change the behaviour of other keys (a becomes A, etc.), it's usually best to press the qualifier key first before the next key, so that you get the alternative function rather than the usual one.
e.g. Try pressing SHIFT & A together, versus hold SHIFT down and press A, and see if you always get a capital A. You don't, always. It may depend on luck, and how your keyboard is scanned. And, depending on what you're trying to do, you may *need* to do exactly what you want, first go.
I've just done this on my laptop, repeatedly, and this is the result: AAAAaAAAAAaaAaAAAAAAAaaAAA
Just the same way as the A key can produce "a" or "A," depending on you using it with the shift key. The PrintScreen/SystemRequest key is a dual purpose key, and which function you get depends on the qualifier key used with it.
So... if you don't quite get the behaviour you expect, press and hold down ALT, first.
On Mon, 2012-08-20 at 14:48 -0700, Rick Stevens wrote:
On 08/20/2012 02:27 PM, Aaron Konstam uttered this comment:
On Mon, 2012-08-20 at 13:20 -0700, Rick Stevens wrote:
On 08/20/2012 01:05 PM, Joe Zeff uttered this comment:
On 08/20/2012 12:55 PM, Aaron Konstam wrote:
It is hard to know where to start with the problems with the use of the SysReg key.. Since acording to the Wikipedia notes in order to get these Magic SysReg features to work you have tp add the Ctrl button. So to reboot you would have to use the Ctrl+Alt+SysReg+ b button. On my workstation Keyboard this is nearly impossible to do because of the position of the SysReg key in the upper right corner of the keyboard. On my laptop where I can hit the keys the function fails to work. Without the Ctrl all you get is screen shots which I do get.
With the alternate approach of: echo key > /proc/sysreq-trigger the reboot works but I can't detect anything else working.
So how does one use these magic keys ?
I can't speak for anybody else, but when I've experimented with it, I used both hands.
It's supposed to be a simultaneous press of ALT, SYSRQ (or PRINTSCREEN) and the command key (B in your case). Note it only works if /proc/sys/kernel/sysrq contains a non-zero value. To enable ALL functionality, first set /proc/sys/kernel/sysrq to the value "1":
echo "1" >/proc/sys/kernel/sysrq
Then hit your key combo. Some keyboards may have issues with so many simultaneous keypresses. In those cases hold down ALT, then press and release SYSRQ, then press and release your command key and finally release ALT.
It's been a while since I futzed with it. If you have the kernel-doc RPM installed, it's explained in
/usr/share/doc/kernel-doc-(version)/Documentation/sysrq.txt
I appreciate all these tips but none make the sysrq suctions work. I'll just give up.
Worked for me on my Dell laptop. Process:
- Did 'echo "1" >/proc/sys/kernel/sysrq'
- Held down left-ALT, held down PRNTSCR, pressed "h"
- Released all three keys
- Ran "dmesg" and saw this:
[111065.967134] SysRq : HELP : loglevel(0-9) reBoot Crash terminate-all-tasks(E) memory-full-oom-kill(F) kill-all-tasks(I) thaw-filesystems(J) saK show-backtrace-all-active-cpus(L) show-memory-usage(M) nice-all-RT-tasks(N) powerOff show-registers(P) show-all-timers(Q) unRaw Sync show-task-states(T) Unmount force-fb(V) show-blocked-tasks(W) dump-ftrace-buffer(Z)
- Did 'echo "0" >/proc/sys/kernel/sysrq' to disable SYSRQ.
Fully updated F17, 3.5.2-1.fc17.x86_64, XFCE and xfwm4 window manager.
First everyone seems to agree that it is the ALT button on the right that needs to be used Theree seems to be general agreement if you don't include the CTRL key only a snapshopt is genrqated the function is not executed. I got the same output as you did but when I uswed b instead of h I goot output about a reboot but it did not occur..
Ther lies the problem. I have 2 Della, a workstation and a laptop and neither work the way they should.
Whne you use b instead of h do you get a reboot?.
On 08/21/2012 01:27 PM, Aaron Konstam wrote:
First everyone seems to agree that it is the ALT button on the right that needs to be used Theree seems to be general agreement if you don't include the CTRL key only a snapshopt is genrqated the function is not executed. I got the same output as you did but when I uswed b instead of h I goot output about a reboot but it did not occur..
I've found that if I add Ctrl, I can use either Alt key, and that pressing them sequentially, but not letting go until all are pressed works best for me. I've not, as yet, tried using b.
Am 20.08.2012 22:36, schrieb Joe Zeff:
Just to be clear, in /etc/sysctl.conf I changed: kernel.sysrq to 1 from 0.
If you've rebooted since doing that, you've turned it off
why should reboot turn it off? /etc/sysctl.conf was, is and will always be for persistent settings
On Tue, 2012-08-21 at 15:27 -0500, Aaron Konstam wrote:
Theree seems to be general agreement if you don't include the CTRL key only a snapshopt is genrqated the function is not executed.
Depends on your user interface... If you're using something like Gnome, it's assigned its own function to ALT and PrintScreen (to screengrab the current active window), versus PrintScreen (by itself, to screengrab the whole desktop).
Whereas, at a basic text-only console, it may be ignoring presses of the PrintScreen/SystemRequest key, and pass it along, for something else to deal with.
The same goes for other hotkeys. Outside of Gnome, for instance, you can switch between terminals simply by pressing ALT and one of the Function keys. Inside Gnome, it's using those key combinations for its own purposes, so another key sequence is used. Again, adding CTRL to it, does the job.
On Tue, 2012-08-21 at 13:38 -0700, Joe Zeff wrote:
On 08/21/2012 01:27 PM, Aaron Konstam wrote:
First everyone seems to agree that it is the ALT button on the right that needs to be used Theree seems to be general agreement if you don't include the CTRL key only a snapshopt is genrqated the function is not executed. I got the same output as you did but when I uswed b instead of h I goot output about a reboot but it did not occur..
I've found that if I add Ctrl, I can use either Alt key, and that pressing them sequentially, but not letting go until all are pressed works best for me. I've not, as yet, tried using b.
Well please try b and let me know if the reboot occurs. The problem is b is the only one where the results are obvious. I am willing to believe that people see the output in dmesg or /var/log/messages, but they don't really know if the action is executed.
On Wed, 2012-08-22 at 07:46 +0200, Heinz Diehl wrote:
On 22.08.2012, Reindl Harald wrote:
why should reboot turn it off?
Because he turned off the option in sysctl.conf, and a reboot will activate it.
Huh, I turned it on not off.
On Wed, 2012-08-22 at 22:32 +0930, Tim wrote:
On Tue, 2012-08-21 at 15:27 -0500, Aaron Konstam wrote:
Theree seems to be general agreement if you don't include the CTRL key only a snapshopt is genrqated the function is not executed.
Depends on your user interface... If you're using something like Gnome, it's assigned its own function to ALT and PrintScreen (to screengrab the current active window), versus PrintScreen (by itself, to screengrab the whole desktop).
Whereas, at a basic text-only console, it may be ignoring presses of the PrintScreen/SystemRequest key, and pass it along, for something else to deal with.
The same goes for other hotkeys. Outside of Gnome, for instance, you can switch between terminals simply by pressing ALT and one of the Function keys. Inside Gnome, it's using those key combinations for its own purposes, so another key sequence is used. Again, adding CTRL to it, does the job.
I did all these things in a alt-f2 console (no Gnome). And they still did not work. I want some one to tell me they hit: cntl+alr+sysrq b and got a reboot.
On 08/22/2012 06:20 AM, Aaron Konstam uttered this comment:
On Wed, 2012-08-22 at 22:32 +0930, Tim wrote:
On Tue, 2012-08-21 at 15:27 -0500, Aaron Konstam wrote:
Theree seems to be general agreement if you don't include the CTRL key only a snapshopt is genrqated the function is not executed.
Depends on your user interface... If you're using something like Gnome, it's assigned its own function to ALT and PrintScreen (to screengrab the current active window), versus PrintScreen (by itself, to screengrab the whole desktop).
Whereas, at a basic text-only console, it may be ignoring presses of the PrintScreen/SystemRequest key, and pass it along, for something else to deal with.
The same goes for other hotkeys. Outside of Gnome, for instance, you can switch between terminals simply by pressing ALT and one of the Function keys. Inside Gnome, it's using those key combinations for its own purposes, so another key sequence is used. Again, adding CTRL to it, does the job.
I did all these things in a alt-f2 console (no Gnome). And they still did not work. I want some one to tell me they hit: cntl+alr+sysrq b and got a reboot.
Running F17/x86_64, fully updated, XFCE/xwfm4 on my Dell N7110 laptop:
1. echo "1" >/proc/sys/kernel/sysrq 2. CTRL+ALT+F2 to get a text console 3. Logged in as root 4. LEFT-ALT+PRSCR+"b" = reboot
To reiterate, that was the left ALT key.
So it works for me, Aaron. ---------------------------------------------------------------------- - Rick Stevens, Systems Engineer, AllDigital ricks@alldigital.com - - AIM/Skype: therps2 ICQ: 22643734 Yahoo: origrps2 - - - - Change is inevitable, except from a vending machine. - ----------------------------------------------------------------------
On 2012/08/22 06:02, Tim wrote:
On Tue, 2012-08-21 at 15:27 -0500, Aaron Konstam wrote:
Theree seems to be general agreement if you don't include the CTRL key only a snapshopt is genrqated the function is not executed.
Depends on your user interface... If you're using something like Gnome, it's assigned its own function to ALT and PrintScreen (to screengrab the current active window), versus PrintScreen (by itself, to screengrab the whole desktop).
Whereas, at a basic text-only console, it may be ignoring presses of the PrintScreen/SystemRequest key, and pass it along, for something else to deal with.
The same goes for other hotkeys. Outside of Gnome, for instance, you can switch between terminals simply by pressing ALT and one of the Function keys. Inside Gnome, it's using those key combinations for its own purposes, so another key sequence is used. Again, adding CTRL to it, does the job.
Even with the reminders I've seen people keep forgetting that most modern keyboards are two key roll-over keyboards. The keys are matrix scanned in a fashion that any two keys pressed at the same time can be detected but more than two keys pressed at the same time is very iffy. You guys may be fighting an inherent keyboard problem rather than an OS deficiency.
I have an animatronics programming application that can use the number keys on a keyboard for controlling the actions of selected channels of the animations. I had to find a true N-Key rollover keyboard to prove it actually worked as advertised with a proper keyboard. Erm, that keyboard was a gaming keyboard from <gisp> Microsoft, in case anybody is wondering.
{^_^}
On 08/22/2012 02:17 PM, jdow wrote:
Even with the reminders I've seen people keep forgetting that most modern keyboards are two key roll-over keyboards. The keys are matrix scanned in a fashion that any two keys pressed at the same time can be detected but more than two keys pressed at the same time is very iffy. You guys may be fighting an inherent keyboard problem rather than an OS deficiency.
That may be why some of the instructions for this call for pressing Alt-SysRq (pause) Command, and why I've had best luck with pressing the keys one at a time and holding them down until all are pressed.
On Wednesday, 22. August 2012. 15.05.05 Joe Zeff wrote:
On 08/22/2012 02:17 PM, jdow wrote:
Even with the reminders I've seen people keep forgetting that most modern keyboards are two key roll-over keyboards. The keys are matrix scanned in a fashion that any two keys pressed at the same time can be detected but more than two keys pressed at the same time is very iffy. You guys may be fighting an inherent keyboard problem rather than an OS deficiency.
That may be why some of the instructions for this call for pressing Alt-SysRq (pause) Command, and why I've had best luck with pressing the keys one at a time and holding them down until all are pressed.
Umm, no, you are *supposed* to keep them pressed. The problem with two-key rollover keyboard is that it will not detect a third keypress until one of the previous two was released. And that is the dealbreaker in using the MagicSysRq functionality.
It is a good thing to understand how this sysrq thing actually works, and for that one needs to know how a keyboard actually works (on a fairly low level).
When a key is pressed, the press-scancode of that key is sent to the keyboard buffer. When the key is released, the release-scancode of that key is sent. Note that press-scancode and release-scancode are different things. If you press the key and keep it pressed, eventually the keyboard-repeat functionality kicks in, and the press-scancode starts being sent over and over. All keys on the keyboard work that way (and I mean *all*, bar maybe the "Fn" key on some laptops).
The press- and release-scancodes in the keyboard buffer are being interpreted by the kernel, translated via a table into keypress/keyrelease combinations, and then sent down to everything else, including X and stuff. Now, the kernel can react (independently of anything else) to some specific scancode combinations, before any other app even gets the idea that something was pressed on the keyboard. That's where the MagicSysRq functionality kicks in.
The trick is that this specific scancode combo that needs to be sent to the kernel needs to be convoluted enough so that it cannot occur accidentally. Therefore, it is a sequence of *press-scancodes*, corresponding to the combinations such as ctrl+alt+sysrq+b, and no release-scancodes in between. This means the following:
(1) you need to press the buttons in *that* particular *order* , one by one, (2) you must not release any of them until all have been pressed, (3) you must be fast enough so that keyboard-repeat doesn't kick in (most commonly this means faster than 1/4 of a second), (4) your keyboard hardware must be able to detect four keys pressed in a row (without releasing any of them).
Various cheap keyboards cannot satisfy (4), various people are not fast enough for (3), and various instruction manuals do not emphasize (1) and (2) well- enough.
In addition to this, note that left-ctrl/shift/alt have *different* scancodes than right-ctrl/shift/alt. I am not sure if the kernel is designed to watch out for all combinations (ll, lr, rl, rr), nor the interchange in order of ctrl and alt. So it is best to try out all combinations, to be certain.
Finally, the "b" key is where "b" is meant to be on a QWERTY keyboard. If you have a keyboard with a different layout (DVORAK for example), this key will likely be labbeled as something else, so watch out for that.
There is a nice table with all keys and their functions in sysrq mode here:
http://en.wikipedia.org/wiki/Magic_SysRq_key
As a side note, I've also seen keyboards with a spacebar that has two "key"- mechanisms beneath (on the left and right side), so that two different press- scancodes are being sent when you press the spacebar, detecting whether you have pressed it from the left or right side. This was exploited in some pinball games, with options "kick the pinball machine with the left/right foot" were simulated by pressing the spacebar from the left or from the right... ;-)
If you want to experiment with scancodes and keycodes, read "man showkey" and try it out in the text terminal (outside X).
HTH, :-) Marko
Am 22.08.2012 15:20, schrieb Aaron Konstam:
On Wed, 2012-08-22 at 22:32 +0930, Tim wrote:
On Tue, 2012-08-21 at 15:27 -0500, Aaron Konstam wrote:
Theree seems to be general agreement if you don't include the CTRL key only a snapshopt is genrqated the function is not executed.
Depends on your user interface... If you're using something like Gnome, it's assigned its own function to ALT and PrintScreen (to screengrab the current active window), versus PrintScreen (by itself, to screengrab the whole desktop).
Whereas, at a basic text-only console, it may be ignoring presses of the PrintScreen/SystemRequest key, and pass it along, for something else to deal with.
The same goes for other hotkeys. Outside of Gnome, for instance, you can switch between terminals simply by pressing ALT and one of the Function keys. Inside Gnome, it's using those key combinations for its own purposes, so another key sequence is used. Again, adding CTRL to it, does the job.
I did all these things in a alt-f2 console (no Gnome). And they still did not work. I want some one to tell me they hit: cntl+alr+sysrq b and got a reboot.
i explained you in my last mail that CTRL+ALT+PRINT+B is plain stoopid, so nobody will do this - i CONFIRMED multiple times that STRG+ALT+PRINT+S does a sync, i hear the drives and i get messages in dmesg, /var/log/messages AND also in a ALT-F2 console independent if there is a login or not, if there is the login-prompt i get
SysRq : Emergency Sync Emergency Sync complete
directly below the prompt
Am 22.08.2012 15:13, schrieb Aaron Konstam:
Well please try b and let me know if the reboot occurs. The problem is b is the only one where the results are obvious. I am willing to believe that people see the output in dmesg or /var/log/messages, but they don't really know if the action is executed.
sure
S: you hear the emegency.sync on a RAID10 device K: i see that if KDE freezes a come back to Login
B: you SHOULD NEVER use it alone because you could also use hardware-reset
posted many times but nobody reads docs people telling: http://en.wikipedia.org/wiki/Magic_SysRq_key
unRaw (take control of keyboard back from X), tErminate (send SIGTERM to all processes, allowing them to terminate gracefully), kIll (send SIGKILL to all processes, forcing them to terminate immediately), Sync (flush data to disk), Unmount (remount all filesystems read-only), reBoot.
Hold down the Alt and SysRq (Print Screen) keys. While holding those down, type the following keys in order, several seconds apart: REISUB Computer should reboot.
On Wed, Aug 22, 2012 at 03:17:30PM +0200, Reindl Harald wrote:
Am 22.08.2012 15:13, schrieb Aaron Konstam:
Well please try b and let me know if the reboot occurs. The problem is b is the only one where the results are obvious. I am willing to believe that people see the output in dmesg or /var/log/messages, but they don't really know if the action is executed.
sure
S: you hear the emegency.sync on a RAID10 device K: i see that if KDE freezes a come back to Login
B: you SHOULD NEVER use it alone because you could also use hardware-reset
posted many times but nobody reads docs people telling: http://en.wikipedia.org/wiki/Magic_SysRq_key
unRaw (take control of keyboard back from X), tErminate (send SIGTERM to all processes, allowing them to terminate gracefully), kIll (send SIGKILL to all processes, forcing them to terminate immediately), Sync (flush data to disk), Unmount (remount all filesystems read-only), reBoot.
Hold down the Alt and SysRq (Print Screen) keys. While holding those down, type the following keys in order, several seconds apart: REISUB Computer should reboot.
A mnemonic that helps me remember the above is that REISUB spells BUSIER, backwards.
On 08/22/2012 06:26 AM, Reindl Harald wrote:
i explained you in my last mail that CTRL+ALT+PRINT+B is plain stoopid, so nobody will do this - i CONFIRMED multiple times that STRG+ALT+PRINT+S does a sync, i hear the drives and i get messages in dmesg, /var/log/messages AND also in a ALT-F2 console independent if there is a login or not, if there is the login-prompt i get
SysRq : Emergency Sync Emergency Sync complete
directly below the prompt
That's exactly what I saw when I tried it. I've never tried following it with b, except when (as it turned out) the system wasn't responding to anything, but maybe I will next time I need to reboot anyway.
-
Aaron Konstam -
Fred Smith -
Hakan Koseoglu -
Heinz Diehl -
Hiisi -
jdow -
Joe Zeff -
Konstantin Svist -
Marko Vojinovic -
Reindl Harald -
Rick Stevens -
Tim