Messages in this thread Patch in this message | | | From | Andy Whitcroft <> | Subject | [PATCH 2/3] sysrq documentation: document why the command header only is shown | Date | Wed, 7 Jan 2009 21:49:17 +0000 |
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Document the interactions between loglevel and the sysrq output. Also document how to work round it should output on the console be required.
Signed-off-by: Andy Whitcroft <apw@canonical.com> --- Documentation/sysrq.txt | 18 ++++++++++++++++++ 1 files changed, 18 insertions(+), 0 deletions(-)
diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt index 265f637..a262ffb 100644 --- a/Documentation/sysrq.txt +++ b/Documentation/sysrq.txt @@ -210,6 +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 combination only the header appears on the console, why? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +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 cirtain 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 -- 1.6.0.4.911.gc990
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