Re: Accessing boot menu when GRUB_TIMEOUT=0

[Andrei Borzenkov]

On 12.01.2023 09:28, AAA BBB wrote:
> Dear GRUBbers,
>
> how can I access the boot menu when GRUB_TIMEOUT=0?
>
> I have searched over the net but none of the proposals I found worked.

This really depends on your grub version and distribution.

Historically grub did not have any way to interrupt boot with zero 
timeout. Some distributions had patches to allow interrupt even then.

Then menu handling was changed to check for ESC even with zero timeout 
and finally handling of SHIFT was added. Unfortunately grub handling of 
timeout is rather counter intuitive - there are two different timeout 
loops, one if menu is hidden and another menu is shown. And only the 
first one is interruptible and which one is used depends on settings in 
grub.cfg. To be able to interrupt zero timeout timeout_style must be set 
to hidden or countdown.

And to add even more confusion, it all depends on platform. E.g. on EFI 
lone SHIFT will be ignored (due to the way underlying firmware works); 
you need to use SHIFT-non-ASCII character to more or less "reliably" let 
grub to detect pressed SHIFT (like SHIFT-F7).

So show your grub.cfg and tell your grub version then it may be possible 
to make some suggestions.

> For instance, here
> <https://unix.stackexchange.com/questions/219061/grub-boot-loader-set-timeout-0-how-to-get-the-boot-menu>
> it is suggested to press ESC or SHIFT after post, here
> <https://askubuntu.com/questions/262965/grub-timeout-set-to-0-cant-access-grub-menu-anymore>
> it is suggested to press SHIFT as well.
>
> I asked because my system did not boot anymore and I had to boot into an
> emergency shell.
>
> Thank you and best regards.
>
> P
>
> ​