write in 30M

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2024-02-20 ea08eeccae9297f7aabd2ef7f0c2517ac4549acc

 kernel/Documentation/admin-guide/sysrq.rst
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 How do I use the magic SysRq key?
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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-On x86   - You press the key combo :kbd:`ALT-SysRq-<command key>`.
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+On x86
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+	You press the key combo :kbd:`ALT-SysRq-<command key>`.
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-.. note::
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+	.. note::
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 	   Some
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            keyboards may not have a key labeled 'SysRq'. The 'SysRq' key is
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            also known as the 'Print Screen' key. Also some keyboards cannot
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 	   have better luck with press :kbd:`Alt`, press :kbd:`SysRq`,
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 	   release :kbd:`SysRq`, press :kbd:`<command key>`, release everything.
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-On SPARC - You press :kbd:`ALT-STOP-<command key>`, I believe.
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+On SPARC
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+	You press :kbd:`ALT-STOP-<command key>`, I believe.
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 On the serial console (PC style standard serial ports only)
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         You send a ``BREAK``, then within 5 seconds a command key. Sending
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         ``BREAK`` twice is interpreted as a normal BREAK.
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 On PowerPC
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-	Press :kbd:`ALT - Print Screen` (or :kbd:`F13`) - :kbd:`<command key>`,
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+	Press :kbd:`ALT - Print Screen` (or :kbd:`F13`) - :kbd:`<command key>`.
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         :kbd:`Print Screen` (or :kbd:`F13`) - :kbd:`<command key>` may suffice.
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 On other
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         let me know so I can add them to this section.
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 On all
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-	write a character to /proc/sysrq-trigger.  e.g.::
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+	Write a character to /proc/sysrq-trigger.  e.g.::
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 		echo t > /proc/sysrq-trigger
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+The :kbd:`<command key>` is case sensitive.
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 What are the 'command' keys?
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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 useful when you want to exit a program that will not let you switch consoles.
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 (For example, X or a svgalib program.)
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-``reboot(b)`` is good when you're unable to shut down. But you should also
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-``sync(s)`` and ``umount(u)`` first.
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+``reboot(b)`` is good when you're unable to shut down, it is an equivalent
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+of pressing the "reset" button.
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 ``crash(c)`` can be used to manually trigger a crashdump when the system is hung.
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 Note that this just triggers a crash if there is no dump mechanism available.
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-``sync(s)`` is great when your system is locked up, it allows you to sync your
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-disks and will certainly lessen the chance of data loss and fscking. Note
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-that the sync hasn't taken place until you see the "OK" and "Done" appear
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-on the screen. (If the kernel is really in strife, you may not ever get the
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-OK or Done message...)
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+``sync(s)`` is handy before yanking removable medium or after using a rescue
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+shell that provides no graceful shutdown -- it will ensure your data is
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+safely written to the disk. Note that the sync hasn't taken place until you see
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+the "OK" and "Done" appear on the screen.
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-``umount(u)`` is basically useful in the same ways as ``sync(s)``. I generally
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-``sync(s)``, ``umount(u)``, then ``reboot(b)`` when my system locks. It's saved
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-me many a fsck. Again, the unmount (remount read-only) hasn't taken place until
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-you see the "OK" and "Done" message appear on the screen.
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+``umount(u)`` can be used to mark filesystems as properly unmounted. From the
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+running system's point of view, they will be remounted read-only. The remount
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+isn't complete until you see the "OK" and "Done" message appear on the screen.
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 The loglevels ``0``-``9`` are useful when your console is being flooded with
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 kernel messages you do not want to see. Selecting ``0`` will prevent all but
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 handler is called. Your handler must conform to the prototype in 'sysrq.h'.
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 After the ``sysrq_key_op`` is created, you can call the kernel function
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-``register_sysrq_key(int key, struct sysrq_key_op *op_p);`` this will
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+``register_sysrq_key(int key, const struct sysrq_key_op *op_p);`` this will
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 register the operation pointed to by ``op_p`` at table key 'key',
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 if that slot in the table is blank. At module unload time, you must call
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-the function ``unregister_sysrq_key(int key, struct sysrq_key_op *op_p)``, which
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-will remove the key op pointed to by 'op_p' from the key 'key', if and only if
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-it is currently registered in that slot. This is in case the slot has been
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-overwritten since you registered it.
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+the function ``unregister_sysrq_key(int key, const struct sysrq_key_op *op_p)``,
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+which will remove the key op pointed to by 'op_p' from the key 'key', if and
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+only if it is currently registered in that slot. This is in case the slot has
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+been overwritten since you registered it.
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 The Magic SysRQ system works by registering key operations against a key op
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 lookup table, which is defined in 'drivers/tty/sysrq.c'. This key table has
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 Credits
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 ~~~~~~~
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-Written by Mydraal <vulpyne@vulpyne.net>
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-Updated by Adam Sulmicki <adam@cfar.umd.edu>
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-Updated by Jeremy M. Dolan <jmd@turbogeek.org> 2001/01/28 10:15:59
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-Added to by Crutcher Dunnavant <crutcher+kernel@datastacks.com>
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+- Written by Mydraal <vulpyne@vulpyne.net>
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+- Updated by Adam Sulmicki <adam@cfar.umd.edu>
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+- Updated by Jeremy M. Dolan <jmd@turbogeek.org> 2001/01/28 10:15:59
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+- Added to by Crutcher Dunnavant <crutcher+kernel@datastacks.com>