Info Catalog
grub: Measured Boot
grub: Security
18.6 Lockdown when booting on a secure setup
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The GRUB can be locked down when booted on a secure boot environment,
for example if the UEFI secure boot is enabled. On a locked down
configuration, the GRUB will be restricted and some operations/commands
cannot be executed.
The 'lockdown' variable is set to 'y' when the GRUB is locked down.
Otherwise it does not exit.