Monday Mission: The Grinch Stole the Bootloader

[TudorRaduta]

No menu. No Config. Just Commands

Happy holidays. This is our final challenge of the year.

You reboot the main application server after a kernel update. Instead of a clean menu, the screen drops you into this:

grub>

No kernel list. No countdown. No safety net. The GRUB configuration is gone or corrupted, and production is waiting.

The Mission

You cannot reinstall the OS. The data matters. The clock is ticking.

Your task is to manually guide the system from the grub> prompt all the way into a running Linux system so you can repair it properly.

️ The Map

At the GRUB prompt, you are not in Linux. You are talking directly to the bootloader. Different rules apply.

• ls shows disks and partitions, such as (hd0,msdos1).
• linux loads the kernel into memory.
• initrd loads the initial RAM disk with drivers.
• boot hands control to the kernel.

Your Challenge

You have identified the boot partition as (hd0,msdos1). To recover the system, you must issue the correct commands in the correct order.

1. Load the Kernel: What is the full linux command, including the required argument that tells the kernel where the root filesystem lives?
2. Load the Ramdisk: What command brings in the matching initramfs so the kernel can actually access disks?
3. Boot: What single command transfers control and starts the system?
4. Make It Stick: Once the system is up, what command regenerates a clean grub.cfg so the next reboot works normally?

• Bonus: On UEFI systems, the config file path is different. Do you know where GRUB expects it?

If you can recover a system from this prompt, you earn serious sysadmin credibility. Let’s see how you’d bring it back.

[Priyanshu20041]

When the system drops to the grub> prompt after a reboot, the goal is to manually load the kernel and initramfs, then boot the OS.

1. Load the kernel

# linux (hd0,msdos1)/vmlinuz-<kernel-version> root=/dev/sda1 ro

The root= parameter tells the kernel where the root filesystem is located.

2. Load the initramfs

 # initrd (hd0,msdos1)/initramfs-<kernel-version>.img

This provides the required drivers to access disks and mount the root filesystem

3 Boot the system

# boot

4. Make the fix permanent (after login)

# grub2-mkconfig -o /boot/grub2/grub.cfg

5 GRUB loads its configuration from:

# /boot/efi/EFI/<distro>/grub.cfg

Understanding the boot flow makes recovery possible even when the menu is gone.

[Priyanshu20041]

From the gurb> prompt, after identifying (hd0,msdos1) as /boot :

1. Load the kernel

# linux (hd0,msdos1)/vmlinuz-<version> root=/dev/sda2 ro

2.Load the initramfs

# initrd (hd0,msdos1)/initramfs-<version>.img

3.Boot the system

 # boot

4.Persist the fix (once logged in)

# grub2-mkconfig -o /boot/grub2/grub.cfg

# /boot/efi/EFI/<distro>/grub.cfg

Manually recovering a system from a raw GRUB prompt is a core sysadmin skill — this is exactly where understanding the boot process matters.