Bug#984520: 'error: symbol "grub_register_command_lockdown" not found' and then lightdm fails to start

[Colin Watson]

On Thu, Jun 03, 2021 at 11:07:27AM +0200, Jesús Ángel wrote:
> I am also facing this error every now and then. Sometimes GRUB doesn't
> boot and keeps showing "error: symbol `grub_register_command_lockdown'
> not found.".
> On pressing any key, GRUB restarts and I get the same error again.

If you're getting this non-deterministically, it suggests that you have
multiple possible boot disks and either your firmware is picking one or
the other inconsistently, or GRUB isn't properly configured to install
to the right ones.  You should run "dpkg-reconfigure grub-pc" and select
all the disks that your firmware might boot from at the "GRUB install
devices:" prompt.

-- 
Colin Watson (he/him)                              [cjwatson at debian.org]