path: root/Documentation/sysrq.txt
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authorIngo Molnar <mingo@elte.hu>2009-01-18 20:15:05 +0100
committerIngo Molnar <mingo@elte.hu>2009-01-18 20:15:05 +0100
commit4092762aebfe55c1f8e31440b80a053c2dbe519b (patch)
tree8fb9fd14131194174c12daf5d8195afd3b62bc3e /Documentation/sysrq.txt
parent745b1626dd71ce9661a05ea4db57859ed5c773d2 (diff)
parent1de9e8e70f5acc441550ca75433563d91b269bbe (diff)
Merge branch 'tracing/ftrace'; commit 'v2.6.29-rc2' into tracing/core
Diffstat (limited to 'Documentation/sysrq.txt')
1 files changed, 18 insertions, 1 deletions
diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
index 56b53e005d18..535aeb936dbc 100644
--- 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?
@@ -213,6 +212,24 @@ 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