[SOLVED] System boots without GRUB menu

[Silent Observer]

I installed Kubuntu 22.04 (after a failed upgrade from Kubuntu 20.04). A week or so later, my motherboard failed; after getting a refurbished/tested motherboard from China (obsolete hardware...) and installing it, I can't get a GRUB menu on startup, either in Legacy or UEFI boot mode. My old motherboard gave slightly different versions of GRUB in either mode.

I have a Boot Repair live USB, but after how it mangled things during my Kubuntu install a few weeks ago, I'm afraid to try running it again. Is there a practical way to reinstall and update GRUB from within Kubuntu or the command line, without the cryptic, easy-to-misunderstand or -misapply process of the Boot Repair live USB? I've tried reinstalling grub-efi-amd64-signed and its dependencies, along with shim-signed (they were being held by Synaptic, but I got them to reinstall from CLI apt) -- but no change.

At present, I have my UEFI/BIOS settings to start in Legacy-only mode, but I've tried UEFI-only, and both in both orders without change.

System: AMD FX8350 (8 cores/8 threads, 4.1 GHz max), 32 GB DDR3-1600, nVidia GTx 1070/4 GB in x16 slot, Gigabyte GA-970A-D3P

[Snowhog]

When you are logged in and on your Desktop, launch Dolphin and navigate to /etc/default and right-click on the file grub and select Open with Kate. Change the line GRUB_TIMEOUT_STYLE= so it reads GRUB_TIMEOUT_STYLE=menu

Click on File > Save and when prompted, type in your login password. Close Kate. Open a konsole and type: sudo update-grub2

Reboot.

[Silent Observer]

Yep, that fixed it. Thanks, Snowhog -- now I have (if I need it) access to older kernels and Memtest86+. I'm not a dual booter, so my system is usable without this, but I *have* had issues (since going Linux full time in 2014) where a kernel update wouldn't boot...

[claydoh]

A super-secret method to bring up Grub in a single boot system without a boot menu showing is to hit the <esc> key for EFI sytems at the right spot after the initial firmware/bios POST screen, or the <shift> key for BIOS systems.
This can be trickier than it sounds, and spamming the key just ends up bypassing it, lol.