Alternate Ways To Invoke Magic SysRq
While this was originally implemented as part of the kernel's keyboard handler for debugging, the functionality has been also exposed via the proc filesystem and is commonly used to provide extended management capabilities to headless and remote systems. As an example, shell script can be simply used:
echo b > /proc/sysrq-triggerThis is equivalent to the key combination Alt+SysRq+B which reboots the machine.
The Linux daemons sysrqd and tcpconsole provide a method of accessing SysRq features over a TCP connection after authenticating with a plain-text password.
The Xen hypervisor has functionality to send magic commands to hosted domains via its "xm sysrq" command.
Many embedded systems have no attached keyboard, but instead use a serial console for text input/output to the running system. It is possible to invoke a Magic SysRq feature over a serial console by sending a 'break' serial command, followed by the desired key. The method of sending a break is dependent on the terminal program or hardware used to connect to the serial console.
For minicom, a popular serial terminal program, the command sequence: 'ctrl-a f' will initiate a break sequence. So the command: 'ctrl-a f m' would show memory information about the system.
Read more about this topic: Magic Sys Rq Key
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