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SubjectRe: [PATCH 2/3] sysrq documentation: document why the command header only is shown
Andy Whitcroft wrote:
> 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 <>
> ---
> 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?

* When I hit a sysrq key 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


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