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Diffstat (limited to 'Documentation/admin-guide/sysrq.rst')
| -rw-r--r-- | Documentation/admin-guide/sysrq.rst | 29 |
1 files changed, 19 insertions, 10 deletions
diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst index 2f2e5bd440f9..9c7aa817adc7 100644 --- a/Documentation/admin-guide/sysrq.rst +++ b/Documentation/admin-guide/sysrq.rst @@ -49,26 +49,26 @@ How do I use the magic SysRq key? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ On x86 - You press the key combo :kbd:`ALT-SysRq-<command key>`. + 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 :kbd:`Alt`, press :kbd:`SysRq`, - release :kbd:`SysRq`, press :kbd:`<command key>`, release everything. + have better luck with press `Alt`, press `SysRq`, + release `SysRq`, press `<command key>`, release everything. On SPARC - You press :kbd:`ALT-STOP-<command key>`, I believe. + You press `ALT-STOP-<command key>`, I believe. On the serial console (PC style standard serial ports only) You send a ``BREAK``, then within 5 seconds a command key. Sending ``BREAK`` twice is interpreted as a normal BREAK. On PowerPC - Press :kbd:`ALT - Print Screen` (or :kbd:`F13`) - :kbd:`<command key>`. - :kbd:`Print Screen` (or :kbd:`F13`) - :kbd:`<command key>` may suffice. + Press `ALT - Print Screen` (or `F13`) - `<command key>`. + `Print Screen` (or `F13`) - `<command key>` may suffice. On other If you know of the key combos for other architectures, please @@ -88,7 +88,7 @@ On all echo _reisub > /proc/sysrq-trigger -The :kbd:`<command key>` is case sensitive. +The `<command key>` is case sensitive. What are the 'command' keys? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -161,6 +161,8 @@ Command Function will be printed to your console. (``0``, for example would make it so that only emergency messages like PANICs or OOPSes would make it to your console.) + +``R`` Replay the kernel log messages on consoles. =========== =================================================================== Okay, so what can I use them for? @@ -211,14 +213,21 @@ processes. "just thaw ``it(j)``" is useful if your system becomes unresponsive due to a frozen (probably root) filesystem via the FIFREEZE ioctl. +``Replay logs(R)`` is useful to view the kernel log messages when system is hung +or you are not able to use dmesg command to view the messages in printk buffer. +User may have to press the key combination multiple times if console system is +busy. If it is completely locked up, then messages won't be printed. Output +messages depend on current console loglevel, which can be modified using +sysrq[0-9] (see above). + Sometimes SysRq seems to get 'stuck' after using it, what can I do? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When this happens, try tapping shift, alt and control on both sides of the keyboard, and hitting an invalid sysrq sequence again. (i.e., something like -:kbd:`alt-sysrq-z`). +`alt-sysrq-z`). -Switching to another virtual console (:kbd:`ALT+Fn`) and then back again +Switching to another virtual console (`ALT+Fn`) and then back again should also help. I hit SysRq, but nothing seems to happen, what's wrong? @@ -281,7 +290,7 @@ 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 :kbd:`alt-sysrq-8` or:: +to temporarily up the console loglevel using `alt-sysrq-8` or:: echo 8 > /proc/sysrq-trigger |