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Pause GRUB booting


From: Robert Middleton
Subject: Pause GRUB booting
Date: Tue, 11 Apr 2017 11:59:08 -0400

I'm trying to modify GRUB to pause booting if a user presses a button
that is connected to a USB<->Serial converter.  This is a bit of an
odd situation, so here's a quick overview:

On occasion, we need to allow end-users to pause booting to allow for
HDD recovery.  This can only happen before GRUB attempts to write to
the HDD, otherwise the system stays broken.  The system has no
keyboard, but it does have hard buttons that send a serial message
over an FTDI usb to serial converter.  I have tried editing grub.cfg
to insert the FTDI module, but I don't see exactly how to read data
from an arbitrary serial port and continue on if there is no data on
the serial line.  There are also about 6 FTDIs on the system, so
knowing which one to read from is important.  My backup plan is to
pause the boot for 30 seconds each time, but I'm trying to avoid
that(plus the wait still has to happen before any data gets written to
the disk).

Is this possible to achieve, or would it require hacking of GRUB code directly?

I'm using Ubuntu 12.04, dpkg reports that GRUB is 1.99-21ubuntu3.17.

-Robert Middleton



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