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Topic: SysRq

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	SysRq - Wikipedia, the free encyclopedia
		SysRq or SysReq (short for System Request) is a key on keyboards for PCs that has no standard use.
		The default BIOS keyboard routines simply ignore SysRq and return without taking action.
		Third-party TSRs existed that used SysRq to provide a form of "panic button" to terminate the program and return the user to the DOS command prompt.
	en.wikipedia.org /wiki/SysRq (367 words)

	Wikipedia: SysRq
		There is a key labeled SysRq on keyboards for PCs that no longer has a standard use.
		When software that has the potential to completely lock up the system is run, a BIOS interrupt is the only input that could be generated; the SysRq BIOS interrupt handler can then be written as a form of "panic button" to gracefully terminate the program or reboot the system.
		In Linux systems, provided the kernel has been compiled with the correct option, the key can be used to perform a variety of functions in an emergency, such as syncing disks, killing processes and powering off the computer.
	www.factbook.org /wikipedia/en/s/sy/sysrq.html (203 words)

	plus-linux.de: SysRq
		Note that previous versions disabled sysrq by default, and you were required to specifically enable it at run-time.
		The 'SysRq' key is also known as the 'Print Screen' key.
		Then use 'setkeycodes 84' to define this sequence to the usual SysRq code (84 is decimal for 0x54).
	www.plus-linux.de /wiki.cgi?SysRq (1362 words)

	SysRq: The Process-nuke LG #81
		Magic SysRq is a key combination directly intercepted by the kernel and can be used, among other things, to perform an emergency shutdown.
		Since it is implemented as a part of the keyboard driver, it is guaranteed to work most of the time, unless the kernel itself is dead.
		If you press SysRq again, the state is changed to up, and further keystrokes are handed to whatever program requests it.
	linuxgazette.net /issue81/vikas.html (812 words)

	Network Security \| IT Security \| Vulnerability Assessment \| Intrusion Prevention
		The implementation in SysRq version 1.0 caused blue-screens on Windows XP and later, necessitating a second version which is universal and is perhaps a more elegant solution anyway.
		SysRq v1.0 employs the same technique in order to install a small PspInitializeSystemDll hook function in NTOSKRNL.EXE's DOS code, but this is only the first step.
		For the record, credit for the SysRq concept goes to eEye's Ben Nagy, although he suggested that the interface to the backdoor be a pi symbol in a corner of the screen.
	eeye.com /html/resources/newsletters/vice/VI20051104.asp?... (2962 words)

	[No title] (Site not responding. Last check: 2007-10-12)
		When running on a kernel with SysRq compiled in, it -may be DISABLED at run-time using following command: +configuring the kernel.
		When running a kernel with SysRq compiled in, +/proc/sys/kernel/sysrq controls the functions allowed to be invoked via +the SysRq key.
		By default the file contains 1 which means that every +possible SysRq request is allowed (in older versions SysRq was disabled +by default, and you were required to specifically enable it at run-time +but this is not the case any more).
	www.kernel.org /pub/linux/kernel/people/akpm/patches/2.6/2.6.11/2.6.11-mm3/broken-out/allow-admin-to-enable-only-some-of-the-magic-sysrq-functions.patch (211 words)

	NOVELL: Cool Solutions: Using the "Magic System Request Keys"
		As long as the kernel is not frozen, the SysRq commands make it possible to cleanly kill applications or restart the system.
		Once the SysRq function has been enabled, the keys are used by entering ++.
		Output that a SysRq sequence generates is given on TTY 10 (accessable with ++) and is written to
	www.novell.com /coolsolutions/feature/15751.html (530 words)

	SysRq - Uncyclopedia
		The SysRq key when pressed three times in conjunction with Pause/Break key will reformat your computer, cause it to recognize only half of its memory, run at 1/3 of its processor speed as well as disabling all virus and spyware protection.
		The SysRq key has been pressed exactly twice and 2/3s since the beginning of time.
		Said option is under "kernel hacking" and is called "Enable the magic SysRq key".
	uncyclopedia.org /wiki/SysRq (461 words)

	Marek Zelem : IP Tables network magic SysRq function 0.4
		ipt_sysrq is a new iptables target that allows you to do the same as the magic sysrq key on a keyboard does, but over the network.
		Use the Network Magic SysRq and you will be able to do more than just pressing a reset button.
		But unfortunately, for simplicity, the Network Magic SysRq is based on a single packet request.
	marek.terminus.sk /prog/ipt_sysrq.shtml (589 words)

	Blogger: Email Post to a Friend
		Sysrq key combo forces the kernel to respond it regardless of whatever else it is doing, unless it is completely locked up (dead).
		Using further extension to iptables called ipt_sysrq (new iptables target), which allows you to do the same as the magic sysrq key on a keyboard does, but over the network.
		I'm assuming that you have Magic SysRq key' support is compiled in your kernel.
	www.blogger.com /email-post.g?blogID=6691640&postID=112499434399744934 (584 words)

	Debugging ASR
		Sysrq can be used to debug a system that is in a crashed state.
		To use sysrq, ASR should be disabled to prevent the server from rebooting before we can gather information about the crash from sysrq.
		Logging in is not required to perform sysrq tasks.
	www.cpqlinux.com /asr-debug.html (399 words)

	[No title] (Site not responding. Last check: 2007-10-12)
		When running a kernel with SysRq compiled in, /proc/sys/kernel/sysrq controls the functions allowed to be invoked via the SysRq key.
		By default the file contains 1 which means that every possible SysRq request is allowed (in older versions SysRq was disabled by default, and you were required to specifically enable it at run-time but this is not the case any more).
		The Magic SysRQ system works by registering key operations against a key op lookup table, which is defined in 'drivers/char/sysrq.c'.
	www.kernel.org /pub/scm/linux/kernel/bkcvs/linux-2.5/Documentation/sysrq.txt,v (1838 words)

	Print screen - Wikipedia, the free encyclopedia
		A 102-key PC US English keyboard layout with the print screen key marked in red.
		Print screen (often abbreviated, such as Prt Scr) is a key present on most computer keyboards, typically situated in the same section as the break and SysRq keys.
		Under earlier command-line based operating systems, this caused an exact copy of the current screen output to be sent to the standard printer port, usually LPT1.
	en.wikipedia.org /wiki/Print_screen (185 words)

	The Linux keyboard and console HOWTO: Ctrl-Alt-Del and other special key combinations
		And they do not use your keymap - indeed, are meant for emergency cases where the state of your keymap, or even of the entire kernel, is uncertain.
		This affects Linux users a bit: the SysRq key is not a modifier key, and people report problems using Alt-SysRq-X for various letters or digits X.
		Long ago a similar problem (`ghosting') was caused by the design of the scan matrix: when three keys were pressed a fourth was also seen.
	www.tldp.org /HOWTO/Keyboard-and-Console-HOWTO-8.html (1075 words)

	System isn't responding - MandrivaUsers.org
		The 'SysRq' sequence involves pressing three keys at once, theleft ALT key, the 'SysRq' key (also labeled 'PrtSc' or 'F13') and a letter key:
		If you are doing this then it means that either your system has crashed very badly (this can happen and even the sysrq keys wont work) or the option is disabled in the kernel (it is usually enabled in default kernels).
		After I installed RH8 I realised that SysRq was disabled (when the system crashed, of course).
	mandrivausers.org /index.php?showtopic=993&st=0&p=7001 (778 words)

	The Management Console (Site not responding. Last check: 2007-10-12)
		It calls the generic kernel's SysRq driver, which does whatever is called for by that argument.
		See the SysRq documentation in Documentation/sysrq.txt in your favorite kernel tree to see what letters are valid and what they do.
		By causing UML to flush its data out to disk, the 'sysrq s' will cause the filesystem to be a clean image.
	user-mode-linux.sourceforge.net /mconsole.html (1100 words)

	Kernel debugging with Kprobes (Site not responding. Last check: 2007-10-12)
		Kprobes makes use of the SysRq key, an artifact from the days of DOS that has found many new uses under Linux (see Resources).
		Because probe event handlers run as extensions to the system breakpoint interrupt handler, they have little or no dependence on system facilities -- and so are able to be implanted in the most hostile environments, from interrupt-time, and task-time, to disabled, inter-context switch, and SMP-enabled code paths -- all without adversely skewing system performance.
		This can be made into a Magic SysRq key to defeat spyware, uncleanly reboot, show memory information, kill processes, and more (much more).
	www-128.ibm.com /developerworks/library/l-kprobes.html?ca=dgr-lnxw07Kprobe (1450 words)

	Icebox: Linux Kernel Debugger
		The only requirement is that Magic SysRq keys have been enabled in the running version of the kernel.
		When the SysRq key is pressed, the kernel calls the handler for that key during the keyboard interrupt routine.
		Other interrupts are masked during that handler, so as long as we don't return, the kernel cannot continue to execute, even if a hardware interrupt is generated.
	davemoore.org /icebox (1295 words)

	SysRq Keys Support (Site not responding. Last check: 2007-10-12)
		The "Magic SysRq" keystrokes will then become available (if support is compiled into the kernel — see below).
		The SysRq key is the same as the Print Screen key.
		Linux admins enable SysRq ordinarily only when doing cutting-edge, crash-prone work such as kernel development.
	linuxmafia.com /faq/VALinux-kb/sysrq-keys-support.html (213 words)

	[vox-tech] crashes -- kernel problems?
		If it is a network problem you should be able to repeat on the console...
		That strongly hints that there is a kernel bug or hardware problem locking the machine.
		Once sysrq is working: S, U, B with a little delay between characters=20 is what you will want to use to reboot after a crash.
	www.lugod.org /pipermail/vox-tech/2003-May/005416.html (931 words)

	Magic Sysrq
		The "Magic Sysrequest key" is Alt (left or right Alt key) and Sysrq (up there under Print Screen, next to F12 on most keyboards).
		With this enabled, pressing Alt, SysRq and another key all at the same time can do things like immediately reboot the whole box - and all it takes is the keyboard, no login required.
		If you have this enabled, it can be useful in the case where the system has escaped your control and nothing else is working.
	www.linuxpronews.com /linuxpronews-55-20050510MagicSysrq.html (542 words)

	Debian Grimoire: Magic Sysrq
		All of our servers have the magic SysRq compiled in, if a system hangs, at console you should generally 'S'ync, 'U'mount, then re'B'oot.
		It is a 'magical' key combo you can hit which the kernel will respond to regardless of whatever else it is doing, unless it is completely locked up.
		Some keyboards may not have a key labeled 'SysRq'.
	deb.riseup.net /miscellaneous/magic-sysrq (528 words)

	[No title]
		This is in case the slot has been +overwritten since you registered it.
		+ +The Magic SysRQ system works by registering key operations against a key op +lookup table, which is defined in 'drivers/char/sysrq.c'.
		This key table has +a number of operations registered into it at compile time, but is mutable, +and 4 functions are exported for interface to it: __sysrq_table_lock, +__sysrq_table_unlock, __sysrq_get_key_op, and __sysrq_put_key_op.
	bama.ua.edu /~dunna001/sysrq-register/SysRQ-registration-0.9.linux-2.2.16.patch (679 words)

	magic sysrq with minicom - LinuxQuestions.org
		I have setup minicom for serial console access to a system which is experiencing random lockups.
		I activated sysrq and am able to send Alt-SysRq commands at the system's virtual console.
		Is there something else I need to set on the target system (/etc/inittab) so that I can send the magic sysrq via the serial console.
	www.linuxquestions.org /questions/showthread.php?t=354050 (297 words)

	Diary for Crutcher (Site not responding. Last check: 2007-10-12)
		Well, my SysRQ patch is now up to version 0.10, and I've got one or two people who've looked at it.
		It now patchs Documentation/sysrq.txt as well, and there are some example modules which are a pretty good starting place to learn to code sysrq events.
		I've hacked registration into sysrq in the linux kernel.
	www.advogato.org /person/Crutcher/diary.html?start=6 (265 words)

	Real-Time Preemption: Magic Sysrq p doesn't work \| Linux \| Kernel
		While testing, I noticed that Sysrq p is silently ignored on current RT kernels with RT preemption: The syslog contains a message that Sysrq p
		I checked the code: The sysrq p function is passed a "struct pt_regs *"
		Sysrq t works, but produces by far too much output for that purpose -
	www.gossamer-threads.com /lists/linux/kernel/538341 (877 words)

	LKML: Pavel Machek: Re: [Patch]: Secure SysRQ update for 2.1.10{7,8pre1}.
		It makes it so you can > > > password protect any sysrq keys you want to, instead of only the whole > > > bunch.
		/proc/sys/debug/sysrq_secure is now a string, you echo the > > > command keys for the sysrq commands you want to be secure.
		Example: > > > # cd /proc/sys/debug > > > # cat /etc/sysrqpassword >sysrq_password > > > # echo 'ilb' >sysrq_secure > > > This sets the sysrq password to whatever is in /etc/sysrqpassword.
	lkml.org /lkml/1998/7/8/44 (287 words)

	- What is the SysRq key for? (Site not responding. Last check: 2007-10-12)
		If the translated scan code is 54 hex (for the SysRq key) then INT 9 calls INT 15 AH=85 and doesn't put the keystroke into the keyboard buffer.
		Early ATs have 84-key keyboards, so their BIOS calls INT 15 AH=85 but not 4F.) Thus your program is free to use SysRq for its own purposes, but at the cost of some programming.
		You could hook INT 9, but it's probably easier to hook INT 15 AH=85, which is called when SysRq is pressed or released.
	www.faqs.org /faqs/msdos-programmer-faq/part2/section-20.html (300 words)

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