Merge branch 'topic/vmaster-update' into for-linus

[safe/jmp/linux-2.6] / Documentation / sysrq.txt

diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
index ef19142..9e592c7 100644 (file)
--- a/Documentation/sysrq.txt
+++ b/Documentation/sysrq.txt
@@ -1,6 +1,5 @@
 Linux Magic System Request Key Hacks
 Documentation for sysrq.c
-Last update: 2007-AUG-04
 
 *  What is the magic SysRq key?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -43,7 +42,7 @@ 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 Alt",
+          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.
@@ -85,6 +84,8 @@ On all -  write a character to /proc/sysrq-trigger.  e.g.:
 '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
@@ -93,7 +94,9 @@ On all -  write a character to /proc/sysrq-trigger.  e.g.:
 
 'p'     - Will dump the current registers and flags to your console.
 
-'q'     - Will dump a list of all running timers.
+'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.
 
@@ -207,6 +210,24 @@ 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?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 And I'll answer any questions about the registration system you got, also