hardMultiple ChoiceObjective-mapped
XK0-006 Practice Question: After a kernel upgrade, the system fails to boot
After a kernel upgrade, the system fails to boot. Which file should be edited to configure GRUB2 to boot into the previous kernel version by default?
⚠ Common exam trap
Many candidates confuse the manually editable configuration file (/etc/default/grub) with the generated boot file (/boot/grub2/grub.cfg), leading them to incorrectly edit the latter directly.
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
✓
/etc/default/grub
/etc/default/grub, because this file contains the GRUB2 configuration variables (such as GRUB_DEFAULT) that control which kernel is booted by default. After editing this file, you must run 'grub2-mkconfig -o /boot/grub2/grub.cfg' to regenerate the boot configuration, which sets the previous kernel as the default entry.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
/etc/grub.d/40_custom
Why it's wrong here
Used for custom menu entries, not default boot selection.
- ✗
/boot/grub/grub.conf
Why it's wrong here
Legacy GRUB configuration, not GRUB2.
- ✗
/boot/grub2/grub.cfg
Why it's wrong here
Auto-generated; editing is not recommended as it is overwritten.
- ✓
/etc/default/grub
Why this is correct
Correct configuration file for GRUB2 defaults.
Go deeper
Related to this question
Learn chapter
File Permissions and Ownership
Key term
Kernel
The kernel is the core program of an operating system that manages hardware resources and provides essential services for all other software to run.
Key term
GRUB
GRUB (Grand Unified Bootloader) is a boot loader package that loads and manages the operating system startup process on Linux and other Unix-like systems.
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