History of SysRq

Difference (from prior major revision) (no other diffs)

Changed: 3c3,5

The key is not totally inactive, however. When it is pressed, nothing is stored in the keyboard buffer, but a BIOS function is called. The default handler of that function does nothing and simply returns. Programs can use SysRq simply by creating an interrupt handler to replace the default stub, but most programs have no need for that functionality. Software that has the potential to completely lock up the system, so that a BIOS interrupt is the only input that could be generated, use SysRq as a form of "panic button." e.g., the linux kernel can be compiled with "Magic System Request Key support" (without using the BIOS, most likely).

The key is not totally inactive, however. When it is pressed, nothing is stored in the keyboard buffer, but a BIOS function is called. The default handler of that function does nothing and simply returns. Programs can use SysRq simply by creating an interrupt handler to replace the default stub, but most programs have no need for that functionality. Software that has the potential to completely lock up the system, so that a BIOS interrupt is the only input that could be generated, use SysRq as a form of "panic button."

In Linux systems, provided the kernel has been compiled with the correct option, the key can be used to perform a variety of functions in an emergency, such as syncing disks, killing processes and powering off the computer.

	Revision 5 . . November 19, 2001 8:58 am by SJK
	Revision 4 . . (edit) November 19, 2001 6:01 am by The Epopt
	Revision 3 . . November 19, 2001 3:24 am by Hagedis [e.g., linux panic button.]
	Revision 2 . . November 19, 2001 2:53 am by Stephen Gilbert [adding Talk]
	Revision 1 . . November 18, 2001 1:22 pm by The Epopt [first draft]