What is GRUB in Kali Linux, and how do you configure and repair it?

Key takeaways

• GRUB 2 starts the kernel after BIOS or UEFI hands over control.
• Edit /etc/default/grub, never /boot/grub/grub.cfg directly, then run update-grub.
• Kali uses GRUB 2, with os-prober available for dual-boot detection.
• A broken GRUB is repaired from a live USB using chroot and grub-install.
• Back up the config and know your disk layout before changing the boot loader.

What does GRUB do?

GRUB (GNU GRand Unified Bootloader) is the first program that loads Kali after the firmware has finished its checks. It finds the kernel, loads it with an initial RAM filesystem (initramfs), passes it boot parameters, and starts it. If more than one operating system is installed, GRUB also lets you choose.

The sequence on a typical Kali install:

1. BIOS or UEFI firmware starts.
2. Firmware loads GRUB from the disk (the boot sector on BIOS systems, or an EFI system partition on UEFI systems).
3. GRUB reads its configuration and shows the menu.
4. GRUB loads the Linux kernel and initramfs.
5. The kernel starts and systemd brings up the system.

The official GNU GRUB manual describes every option. Kali itself is covered in the Kali Linux documentation.

Where are GRUB's files?

How do you change GRUB settings?

Edit /etc/default/grub, then regenerate the configuration. Make a backup first.

$ sudo cp /etc/default/grub /etc/default/grub.bak
$ sudo nano /etc/default/grub
$ sudo update-grub

Useful settings:

• GRUB_TIMEOUT=5 is how many seconds the menu waits.
• GRUB_DEFAULT=0 boots the first entry. You can also use a saved entry.
• GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" sets kernel options. Removing quiet splash shows boot messages, which helps when debugging.

update-grub rewrites /boot/grub/grub.cfg from your settings and the scripts in /etc/grub.d/.

How do you boot into recovery mode?

Choose "Advanced options for Kali GNU/Linux" in the GRUB menu, then a recovery entry. You get a root shell that lets you fix passwords or broken packages. You can also press e on a menu entry to edit its options for one boot. Changes made this way are not saved.

How do you repair GRUB when Kali will not boot?

Boot from a Kali live USB, mount your installed system, and reinstall GRUB. First check your layout.

$ lsblk -f

Say Kali's root partition is /dev/sda2 and you boot in UEFI mode with the EFI partition on /dev/sda1. Your device names will differ. Then:

$ sudo mount /dev/sda2 /mnt
$ sudo mount /dev/sda1 /mnt/boot/efi
$ for d in dev dev/pts proc sys run; do sudo mount --bind /$d /mnt/$d; done
$ sudo chroot /mnt
# grub-install /dev/sda
# update-grub
# exit

On a BIOS (legacy) system you skip the EFI mount and run grub-install /dev/sda on the disk, not on a partition. Reboot and remove the USB.

Check ls /sys/firmware/efi in the live session. If the directory exists, you booted in UEFI mode and should use the UEFI steps.

Why does Windows disappear from the GRUB menu?

Dual-boot menus rely on os-prober. On recent Debian-based systems it is disabled by default, so Windows may not appear after an update. To enable it, set GRUB_DISABLE_OS_PROBER=false in /etc/default/grub and run update-grub. Check this against the Kali documentation for your version.

Common mistakes

• Editing grub.cfg directly. The next update-grub erases your change.
• Running grub-install on a partition instead of the disk on BIOS systems.
• Forgetting to mount the EFI partition before the chroot on UEFI systems.
• Setting GRUB_TIMEOUT=0 and then being unable to reach the menu.

What about LILO?

LILO was the older Linux boot loader and is not used on modern Kali. Our LILO explainer covers the history.

Next steps

Understanding boot is basic Linux administration. If you are building those skills, look at our Linux training or read how the Linux file system hierarchy is laid out.

Related reading

• Understanding the Linux File System and Directory Structure | A Complete Guide for Beginners and Professionals