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Fix GRUB that will not boot

We'll confirm where GRUB stops, boot from live USB, chroot, reinstall GRUB, and update the config—or tell you when to escalate.

Troubleshooting · Servers & Linux
30–60 min
What you'll need
  • Live USB (e.g. Ubuntu, Fedora)
  • Root or sudo access
Step 1 of 4

Quick triage — pick your path

Quick triage — pick your path

Choose the option that matches what you see. You can jump straight to that section.

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Steps

Goal: Confirm where the boot stops, boot from live USB, chroot, reinstall GRUB, and update the config.

  • Power on and watch the output. Note whether you see the GRUB menu, a black screen, or an error like “error: file not found.”
  • Good: You know where it stops. Proceed to Boot from live USB.
  • Bad: Screen is blank—check display, try a different monitor or cable.

Boot from live USB

Goal: Boot into a live environment so you can chroot into the installed system.

  • Create a live USB with Ubuntu, Fedora, or your distro. Boot from it (change boot order in BIOS/UEFI if needed).
  • Boot from the live USB. Confirm you see the live desktop or shell.

Mount and chroot

Goal: Mount the root filesystem and chroot into the installed system.

  • Identify the root partition with lsblk or fdisk -l. Mount it: sudo mount /dev/sda1 /mnt. For UEFI, mount the EFI partition: sudo mount /dev/sda2 /mnt/boot/efi.
  • Bind mount: sudo mount --bind /dev /mnt/dev, sudo mount --bind /proc /mnt/proc, sudo mount --bind /sys /mnt/sys. Chroot: sudo chroot /mnt.
  • Confirm you have a root prompt inside the installed system.

Reinstall GRUB

Goal: Reinstall the GRUB boot loader from the chroot.

  • For BIOS: grub-install /dev/sda (use your disk, not partition). For UEFI: grub-install --target=x86_64-efi --efi-directory=/boot/efi.
  • Run update-grub (Debian/Ubuntu) or grub2-mkconfig -o /boot/grub2/grub.cfg (RHEL/Fedora).
  • Exit chroot, unmount, reboot. Confirm the GRUB menu appears and the system boots.

When to get help

Escalate if:

  • grub-install and update-grub complete but the system still does not boot.
  • The disk may have failed (SMART errors, repeated failures).
  • You cannot reach a live environment.

Provide: last error message, whether GRUB ever appeared, BIOS or UEFI, and steps tried.

Verification

  • The GRUB menu appears when the system boots.
  • You can select an entry and the system boots to a login prompt.
  • No “error: file not found” or “error: unknown filesystem” during boot.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Boot from live USB Boot from live USB; mount root and chroot.
  2. Check disk space Free space if root is full.
  3. Reinstall GRUB grub-install and update-grub from chroot.
  4. Escalate Provide last error, disk details, steps tried.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Last visible message before hang or reboot
  • Whether GRUB menu ever appeared
  • BIOS or UEFI
  • Steps already tried

Does the GRUB menu appear or do you see an error?

Black screen, no GRUB, or "error: file not found" means GRUB is corrupted or missing.

Power on and watch the output. No GRUB: GRUB missing or corrupted—reinstall from live USB. GRUB appears: try recovery mode or edit kernel line. Error: note the exact message—often points to missing file or wrong partition.

GRUB appears No GRUB or error

You can change your answer later.

Can you boot an entry or edit the kernel line?

At GRUB, press e to edit. You can add nomodeset or single to get a shell.

At GRUB, select an entry and press e. Add `nomodeset` (display issues) or `single` (shell). Ctrl+X to boot. If the system boots then you can fix the config from inside. Good: system boots. Bad: still fails—reinstall GRUB from live USB.

Yes No

You can change your answer later.

Fix GRUB from inside the system

From a root shell: run `grub-install /dev/sda` (BIOS) or `grub-install --target=x86_64-efi --efi-directory=/boot/efi` (UEFI). Then `update-grub`. Reboot.

Done

Boot from live USB and chroot

Boot from live USB. Mount root, chroot, run grub-install and update-grub.

Boot from live USB. Mount root and EFI (if UEFI). Bind mount /dev, /proc, /sys. Chroot. Run grub-install and update-grub. See Reinstall GRUB for full steps.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would GRUB not boot?
Corrupted GRUB config, missing or wrong boot files, or a failed grub-install. A full disk or filesystem errors can also prevent GRUB from loading. Reinstall GRUB from a live environment.
Can I fix GRUB without a live USB?
If GRUB appears but you cannot boot an entry, you can edit the kernel line at boot (press e). For full reinstall, you need a live USB or rescue environment.
When should I escalate a GRUB boot failure?
If grub-install and update-grub complete but the system still does not boot, the disk may have failed. Check SMART or escalate with disk details.

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