[syslinux] How to show boot prompt and edit kernel cmdline from serial?

Ady Ady ady-sf at hotmail.com
Tue Jan 3 10:01:16 PST 2017

> For testing purposses, I'm trying to hook on QEmu an ISO image that
> start automatically with syslinux (just a DEFAULT label and no TIMEOUT
> option) and change the kernel arguments to redirect the console to a
> serial port instead of the screen.
> So far I've seen that the SERIAL statement give me a welcome message
> and the loading of the kernel and initramfs on the serial port (but
> curiously, not the "Loading NodeOS" message that I put, just directly
> the kernel string...), but the system start automatically. I've read
> in the docs that the boot prompt can be forced to be shown if the
> caps_lock or the scroll_lock keys are set, but QEmu doen't offer a way
> to have them enabled at boot time and by using the monitor seems to be
> too complicated (and since syslinux is booting automatically, too much
> time constrained too). So I ask: is there a way to force to show the
> boot prompt on the serial port on demand? Maybe a magic characters
> sequence I send over the serial port itself after I receive the
> syslinux welcome message?
> -- 
What's wrong with using "PROMPT 1" in your syslinux.cfg?

Generally speaking, posting the entire cfg might help.


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