220-1102 Operating Systems Practice Question
A technician installed Ubuntu Linux on a Windows 10 Pro computer configured for dual-boot. After installation, the computer boots directly into Windows without displaying the GRUB menu. The technician boots from a Linux live USB and opens a terminal. Which command should the technician use FIRST to reinstall GRUB for a UEFI-based system?
⚠ Common exam trap
Watch out — candidates often confuse `grub-install /dev/sda` (MBR/BIOS method) with the UEFI-specific command, or they mistakenly think `update-grub` alone can fix a missing bootloader, when in fact it only updates the menu configuration, not the bootloader installation.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
sudo grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=GRUB
The system is UEFI-based, so GRUB must be installed with the `--target=x86_64-efi` flag to target the EFI firmware, and `--efi-directory=/boot/efi` specifies the EFI System Partition (ESP) mount point. The `--bootloader-id=GRUB` sets the boot entry name in the NVRAM. This command reinstalls GRUB to the ESP, ensuring the firmware can find and boot it.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
sudo grub-install /dev/sda
Why it's wrong here
This command installs GRUB to the MBR of the first disk, which is used for legacy BIOS booting, not UEFI. On a UEFI system, the bootloader must be installed to the EFI System Partition (ESP).
- ✗
sudo update-grub
Why it's wrong here
This command regenerates the GRUB configuration file (grub.cfg) but does not install or reinstall the GRUB bootloader to the ESP. It is useful after changing kernel parameters or adding new operating systems, but it will not fix a missing bootloader.
- ✓
sudo grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=GRUB
Why this is correct
This command correctly installs GRUB to the EFI System Partition (ESP) for a 64-bit UEFI system. It creates the necessary EFI boot entry so that the firmware can load GRUB, which then displays the menu including the Windows Boot Manager option.
- ✗
sudo fdisk -l
Why it's wrong here
sudo fdisk -l only reads and displays the partition table, such as the presence and type of an EFI System Partition (ESP) on /dev/sda. It does not write any bootloader files, format the ESP, or modify the firmware's NVRAM boot entries, so a missing or corrupted GRUB remains unfixed. While it can help confirm that an ESP exists for diagnostic purposes, it is purely a listing tool and cannot restore the UEFI boot path.
Go deeper
Related to this question
Learn chapter
Linux Users and File Permissions
Key term
Terminal
A terminal is a text-based interface that allows users to communicate with a computer's operating system by typing commands.
Key term
Universal Serial Bus
A Universal Serial Bus (USB) is a standard interface that allows you to connect devices like keyboards, mice, storage drives, and printers to a computer for data transfer and power delivery.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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