The patch titled
sysrq documentation: document why the command header only is shown
has been added to the -mm tree. Its filename is
sysrq-documentation-document-why-the-command-header-only-is-shown.patch
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------------------------------------------------------
Subject: sysrq documentation: document why the command header only is shown
From: Andy Whitcroft <apw@xxxxxxxxxxxxx>
Document the interactions between loglevel and the sysrq output. Also
document how to work round it should output be required on the console.
Signed-off-by: Andy Whitcroft <apw@xxxxxxxxxxxxx>
Cc: Martin Mares <mj@xxxxxx>
Cc: Randy Dunlap <randy.dunlap@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/sysrq.txt | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff -puN Documentation/sysrq.txt~sysrq-documentation-document-why-the-command-header-only-is-shown Documentation/sysrq.txt
--- a/Documentation/sysrq.txt~sysrq-documentation-document-why-the-command-header-only-is-shown
+++ a/Documentation/sysrq.txt
@@ -212,6 +212,24 @@ within a function called by handle_sysrq
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
_
Patches currently in -mm which might be from apw@xxxxxxxxxxxxx are
mmc-add-modalias-linkage-for-mmc-sd-devices.patch
sysrq-documentation-remove-the-redundant-updated-date.patch
sysrq-documentation-document-why-the-command-header-only-is-shown.patch
sysrq-add-commentary-on-why-we-use-the-console-loglevel-over-using-kern_emerg.patch
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