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diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt deleted file mode 100644 index 3a3b30ac2a75..000000000000 --- a/Documentation/sysrq.txt +++ /dev/null @@ -1,257 +0,0 @@ -Linux Magic System Request Key Hacks -Documentation for sysrq.c - -* What is the magic SysRq key? -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -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. - -* How do I enable the magic SysRq key? -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -You need to say "yes" to 'Magic SysRq key (CONFIG_MAGIC_SYSRQ)' when -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. The default value in this file is set by the -CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE config symbol, which itself defaults -to 1. Here is the list of possible values in /proc/sys/kernel/sysrq: - 0 - disable sysrq completely - 1 - enable all functions of sysrq - >1 - bitmask of allowed sysrq functions (see below for detailed function - description): - 2 = 0x2 - enable control of console logging level - 4 = 0x4 - enable control of keyboard (SAK, unraw) - 8 = 0x8 - enable debugging dumps of processes etc. - 16 = 0x10 - enable sync command - 32 = 0x20 - enable remount read-only - 64 = 0x40 - enable signalling of processes (term, kill, oom-kill) - 128 = 0x80 - allow reboot/poweroff - 256 = 0x100 - allow nicing of all RT tasks - -You can set the value in the file by the following command: - echo "number" >/proc/sys/kernel/sysrq - -The number may be written here either as decimal or as hexadecimal -with the 0x prefix. CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE must always be -written in hexadecimal. - -Note that the value of /proc/sys/kernel/sysrq influences only the invocation -via a keyboard. Invocation of any operation via /proc/sysrq-trigger is always -allowed (by a user with admin privileges). - -* How do I use the magic SysRq key? -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -On x86 - You press the key combo 'ALT-SysRq-<command key>'. Note - Some - keyboards may not have a key labeled 'SysRq'. The 'SysRq' key is - also known as the 'Print Screen' key. Also some keyboards cannot - handle so many keys being pressed at the same time, so you might - have better luck with "press Alt", "press SysRq", "release SysRq", - "press <command key>", release everything. - -On SPARC - You press 'ALT-STOP-<command key>', I believe. - -On the serial console (PC style standard serial ports only) - - You send a BREAK, then within 5 seconds a command key. Sending - BREAK twice is interpreted as a normal BREAK. - -On PowerPC - Press 'ALT - Print Screen (or F13) - <command key>, - Print Screen (or F13) - <command key> may suffice. - -On other - If you know of the key combos for other architectures, please - let me know so I can add them to this section. - -On all - write a character to /proc/sysrq-trigger. e.g.: - - echo t > /proc/sysrq-trigger - -* What are the 'command' keys? -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -'b' - Will immediately reboot the system without syncing or unmounting - your disks. - -'c' - Will perform a system crash by a NULL pointer dereference. - A crashdump will be taken if configured. - -'d' - Shows all locks that are held. - -'e' - Send a SIGTERM to all processes, except for init. - -'f' - Will call the oom killer to kill a memory hog process, but do not - panic if nothing can be killed. - -'g' - Used by kgdb (kernel debugger) - -'h' - Will display help (actually any other key than those listed - here will display help. but 'h' is easy to remember :-) - -'i' - Send a SIGKILL to all processes, except for init. - -'j' - Forcibly "Just thaw it" - filesystems frozen by the FIFREEZE ioctl. - -'k' - Secure Access Key (SAK) Kills all programs on the current virtual - console. NOTE: See important comments below in SAK section. - -'l' - Shows a stack backtrace for all active CPUs. - -'m' - Will dump current memory info to your console. - -'n' - Used to make RT tasks nice-able - -'o' - Will shut your system off (if configured and supported). - -'p' - Will dump the current registers and flags to your console. - -'q' - Will dump per CPU lists of all armed hrtimers (but NOT regular - timer_list timers) and detailed information about all - clockevent devices. - -'r' - Turns off keyboard raw mode and sets it to XLATE. - -'s' - Will attempt to sync all mounted filesystems. - -'t' - Will dump a list of current tasks and their information to your - console. - -'u' - Will attempt to remount all mounted filesystems read-only. - -'v' - Forcefully restores framebuffer console -'v' - Causes ETM buffer dump [ARM-specific] - -'w' - Dumps tasks that are in uninterruptable (blocked) state. - -'x' - Used by xmon interface on ppc/powerpc platforms. - Show global PMU Registers on sparc64. - Dump all TLB entries on MIPS. - -'y' - Show global CPU Registers [SPARC-64 specific] - -'z' - Dump the ftrace buffer - -'0'-'9' - Sets the console log level, controlling which kernel messages - will be printed to your console. ('0', for example would make - it so that only emergency messages like PANICs or OOPSes would - make it to your console.) - -* Okay, so what can I use them for? -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Well, unraw(r) is very handy when your X server or a svgalib program crashes. - -sak(k) (Secure Access Key) is useful when you want to be sure there is no -trojan program running at console which could grab your password -when you would try to login. It will kill all programs on given console, -thus letting you make sure that the login prompt you see is actually -the one from init, not some trojan program. -IMPORTANT: In its true form it is not a true SAK like the one in a :IMPORTANT -IMPORTANT: c2 compliant system, and it should not be mistaken as :IMPORTANT -IMPORTANT: such. :IMPORTANT - It seems others find it useful as (System Attention Key) which is -useful when you want to exit a program that will not let you switch consoles. -(For example, X or a svgalib program.) - -reboot(b) is good when you're unable to shut down. But you should also -sync(s) and umount(u) first. - -crash(c) can be used to manually trigger a crashdump when the system is hung. -Note that this just triggers a crash if there is no dump mechanism available. - -sync(s) is great when your system is locked up, it allows you to sync your -disks and will certainly lessen the chance of data loss and fscking. Note -that the sync hasn't taken place until you see the "OK" and "Done" appear -on the screen. (If the kernel is really in strife, you may not ever get the -OK or Done message...) - -umount(u) is basically useful in the same ways as sync(s). I generally sync(s), -umount(u), then reboot(b) when my system locks. It's saved me many a fsck. -Again, the unmount (remount read-only) hasn't taken place until you see the -"OK" and "Done" message appear on the screen. - -The loglevels '0'-'9' are useful when your console is being flooded with -kernel messages you do not want to see. Selecting '0' will prevent all but -the most urgent kernel messages from reaching your console. (They will -still be logged if syslogd/klogd are alive, though.) - -term(e) and kill(i) are useful if you have some sort of runaway process you -are unable to kill any other way, especially if it's spawning other -processes. - -"just thaw it(j)" is useful if your system becomes unresponsive due to a frozen -(probably root) filesystem via the FIFREEZE ioctl. - -* Sometimes SysRq seems to get 'stuck' after using it, what can I do? -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -That happens to me, also. I've found that tapping shift, alt, and control -on both sides of the keyboard, and hitting an invalid sysrq sequence again -will fix the problem. (i.e., something like alt-sysrq-z). Switching to another -virtual console (ALT+Fn) and then back again should also help. - -* I hit SysRq, but nothing seems to happen, what's wrong? -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -There are some keyboards that produce a different keycode for SysRq than the -pre-defined value of 99 (see KEY_SYSRQ in include/linux/input.h), or which -don't have a SysRq key at all. In these cases, run 'showkey -s' to find an -appropriate scancode sequence, and use 'setkeycodes <sequence> 99' to map -this sequence to the usual SysRq code (e.g., 'setkeycodes e05b 99'). It's -probably best to put this command in a boot script. Oh, and by the way, you -exit 'showkey' by not typing anything for ten seconds. - -* I want to add SysRQ key events to a module, how does it work? -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -In order to register a basic function with the table, you must first include -the header 'include/linux/sysrq.h', this will define everything else you need. -Next, you must create a sysrq_key_op struct, and populate it with A) the key -handler function you will use, B) a help_msg string, that will print when SysRQ -prints help, and C) an action_msg string, that will print right before your -handler is called. Your handler must conform to the prototype in 'sysrq.h'. - -After the sysrq_key_op is created, you can call the kernel function -register_sysrq_key(int key, struct sysrq_key_op *op_p); this will -register the operation pointed to by 'op_p' at table key 'key', -if that slot in the table is blank. At module unload time, you must call -the function unregister_sysrq_key(int key, struct sysrq_key_op *op_p), which -will remove the key op pointed to by 'op_p' from the key 'key', if and only if -it is currently registered in that slot. 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/tty/sysrq.c'. This key table has -a number of operations registered into it at compile time, but is mutable, -and 2 functions are exported for interface to it: - register_sysrq_key and unregister_sysrq_key. -Of course, never ever leave an invalid pointer in the table. I.e., when -your module that called register_sysrq_key() exits, it must call -unregister_sysrq_key() to clean up the sysrq key table entry that it used. -Null pointers in the table are always safe. :) - -If for some reason you feel the need to call the handle_sysrq function from -within a function called by handle_sysrq, you must be aware that you are in -a lock (you are also in an interrupt handler, which means don't sleep!), so -you must call __handle_sysrq_nolock instead. - -* When I hit a SysRq key combination only the header appears on the console? -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Sysrq output is subject to the same console loglevel control as all -other console output. This means that if the kernel was booted 'quiet' -as is common on distro kernels the output may not appear on the actual -console, even though it will appear in the dmesg buffer, and be accessible -via the dmesg command and to the consumers of /proc/kmsg. As a specific -exception the header line from the sysrq command is passed to all console -consumers as if the current loglevel was maximum. If only the header -is emitted it is almost certain that the kernel loglevel is too low. -Should you require the output on the console channel then you will need -to temporarily up the console loglevel using alt-sysrq-8 or: - - echo 8 > /proc/sysrq-trigger - -Remember to return the loglevel to normal after triggering the sysrq -command you are interested in. - -* I have more questions, who can I ask? -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Just ask them on the linux-kernel mailing list: - linux-kernel@vger.kernel.org - -* Credits -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Written by Mydraal <vulpyne@vulpyne.net> -Updated by Adam Sulmicki <adam@cfar.umd.edu> -Updated by Jeremy M. Dolan <jmd@turbogeek.org> 2001/01/28 10:15:59 -Added to by Crutcher Dunnavant <crutcher+kernel@datastacks.com> |