patch-2.1.93 linux/Documentation/sysrq.txt

• Lines: 90
• Date: Fri Apr 3 17:50:32 1998
• Orig file: v2.1.92/linux/Documentation/sysrq.txt
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.1.92/linux/Documentation/sysrq.txt linux/Documentation/sysrq.txt
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+                      MAGIC SYSRQ KEY DOCUMENTATION v1.0
+                     ------------------------------------
+                        [Fri Apr  3 08:27:12 EST 1998]
+
+1. What is the magic SysRQ key?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It is a 'magical' key combo you can hit, and the kernel will respond to
+regardless of anything else, unless it is hard-locked.
+
+2. How do I enable the magic SysRQ key?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+You need to say yes to 'Magic SysRq key (CONFIG_MAGIC_SYSRQ)' when
+configuring the kernel. This option is only available it 2.1.x or later
+kernels.
+
+3. How do I use the magic SysRQ key?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+You press the key combo 'ALT-SysRQ-<command key>'.
+
+4. What are the 'command' keys?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+'r'     - Turns off keyboard raw mode and sets it to XLATE.
+
+'k'     - Kills all programs on the current virtual console.
+
+'b'     - Will immediately reboot the system without syncing or unmounting
+          your disks.
+
+'o'     - Will shut your system off via APM (if configured and supported).
+
+'s'     - Will attempt to sync all mounted filesystems.
+
+'u'     - Will attempt to remount all mounted file systems readonly.
+
+'p'     - Will dump the current registers and flags to your console.
+
+'t'     - Will dump a list of current tasks and their information to your
+          console.
+
+'m'     - Will dump current memory info to your console.
+
+'0'-'8' - 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.)
+
+'e'     - Send a SIGTERM to all processes, except for init.
+
+'i'     - Send a SIGKILL to all processes, except for init.
+
+'l'     - Send a SIGKILL to all processes, INCLUDING init. (Your system
+          will be non-functional after this.)
+
+5. Okay, so what can I use them for?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Well, un'R'aw is very handy when your X server or a svgalib program crashes.
+
+sa'K' (system attention key) is useful when you want to exit a program
+that will not let you switch consoles. (For example, X or a svgalib program.)
+
+re'B'oot is good when you're unable to shut down. But you should also 'S'ync
+and 'U'mount first.
+
+'S'ync 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.
+
+'U'mount is basically useful in the same ways as 'S'ync. I generally 'S'ync,
+'U'mount, then re'B'oot when my system locks. It's saved me many a fsck.
+
+The loglevel'0'-'8' is useful when your console is being flooded with
+kernel messages you do not want to see. Setting '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.)
+
+t'E'rm and k'I'll 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.
+
+6. 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. (ie, something like alt-sysrq-z).
+
+7. I have more questions, who can I ask?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+You may feel free to send email to myrdraal@deathsdoor.com, and I will
+respond as soon as possible.
+ -Myrdraal