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efivars is gone with Debian/bullseye #newinbullseye

Continuing with #newinbullseye, it’s worth being aware of, that efivars is gone with the kernel version shipped as of Debian/bullseye.

Quoting from wiki.debian.org/UEFI:

The Linux kernel gives access to the UEFI configuration variables via a set of files under /sys, using two different interfaces.

The older interface was showing files under /sys/firmware/efi/vars, and this is what was used by default in both Wheezy and Jessie.

The new interface is efivarfs, which will expose things in a slightly different format under /sys/firmware/efi/efivars.
This is the new preferred way of using UEFI configuration variables, and Debian switched to it by default from Stretch onwards.

Now, CONFIG_EFI_VARS is no longer enabled in Debian due to commit 20146398c4 (shipped as such with Debian kernel package versions >=5.10.1-1~exp1).

As a result, the kernel module efivars is no longer available on systems running Debian kernels >=5.10 (which includes Debian/bullseye). Now, when running such a system in EFI mode, chroot-ing into a system and executing e.g. efibootmgr, it might fail with:

# efibootmgr
EFI variables are not supported on this system.

This is caused by /sys/firmware/efi/vars no longer being available, because of the disabled CONFIG_EFI_VARS. To get this working again, you need to make efivarfs available via:

# mount -t efivarfs efivarfs /sys/firmware/efi/efivars

Then efibootmgr and further tools relying on efivars should work again.

FYI: if you’re a user of Grml’s grml-chroot tool, this is going to be handled out of the box for you.

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