efibootmgr is a userspace application used to modify the Intel Extensible Firmware Interface (EFI) Boot Manager. This application can create and destroy boot entries, change the boot order, change the next running boot option, and more.

efibootmgr
efibootmgr –help
sudo efibootmgr -v
sudo efibootmgr -b 2 -B
sudo update-grub

-v | –verbose
Verbose mode – prints additional information

-b | –bootnum XXXX
Modify BootXXXX (hex)

-B | –delete-bootnum
Delete bootnum (hex)

/boot/efi/EFI/ubuntu

What is the difference between grubx64 and shimx64?

Typically, EFI/ubuntu/grubx64.efi on the EFI System Partition (ESP) is the GRUB binary, and EFI/ubuntu/shimx64.efi is the binary for shim. The latter is a relatively simple program that provides a way to boot on a computer with Secure Boot active. On such a computer, an unsigned version of GRUB won’t launch, and signing GRUB with Microsoft’s keys is impossible, so shim bridges the gap and adds its own security tools that parallel those of Secure Boot. In practice, shim registers itself with the firmware and then launches a program called grubx64.efi in the directory from which it was launched, so on a computer without Secure Boot (such as a Mac), launching shimx64.efi is just like launching grubx64.efi. On a computer with Secure Boot active, launching shimx64.efi should result in GRUB starting up, whereas launching grubx64.efi directly probably won’t work.

Identifying if the computer boots the HDD in UEFI mode

[ -d /sys/firmware/efi ] && echo “EFI boot on HDD” || echo “Legacy boot on HDD”

How To Safely Remove Old Linux Kernels In Ubuntu.

sudo apt install byobu

sudo purge-old-kernels

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