On a typical laptop, you need to press the Fn key to press SysRq. If you also press the letter in the same movement, you end up pressing Fn+Alt+SysRq+letter. But several letters are mapped to numeric keypad keys when combined with Fn. For example, if you try to press Alt+SysRq+U, you end up pressing Alt+SysRq+Num4 instead.
To avoid this pitfall, press and hold Alt, then a press and release SysRq (using Fn if necessary), then press and release the magic SysRq function letter, and finally release Alt. For example: hold Alt, hold Fn, press and release Del, release Fn, press and release U, release Alt.
I'm not sure if that's your problem, as B is typically not a numpad key on laptops. It may be a vendor-specific key; if Fn+B is not equivalent to plain B, then you need to release Fn mid-sequence.
Yes, this is possible, at least from NoVNC with KVM based guest. The trick is to understand that VNC has been built for X11. Hence, on the wire, the keycodes you need to send are the one used internally by X11.
In this specific use case, this is:
0xffe9 --> alt
0xff15 --> sysrq
0x0062 --> b
Sources
Best Answer
Assuming you have a kernel with the debugger option compiled in you can use ControlAltEscape. From there you can
call boot(0)orpanic.Chapter 10 of the FreeBSD developers handbook explains this in a lot more detail.
So much for more or less the same as SysReq via a keyboard. On the serial console, you need to send the break signal and have the
options BREAK_TO_DEBUGGERenabled. But "it is not the default since there are a lot of serial adapters around that gratuitously generate a BREAK condition, for example when pulling the cable".