How to Repair Ubuntu Boot Issues (Step-by-Step Guide)

If your Ubuntu system refuses to boot — stuck at a black screen, a grub rescue> prompt, or an endless reboot loop — don’t panic. This guide walks you through how to repair Ubuntu boot issues step-by-step, using both built-in tools and the Boot-Repair utility.

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🧩 Common Symptoms

Before fixing, identify what type of boot problem you have:

• Black screen or blinking cursor after BIOS/UEFI logo
• grub rescue> or grub> prompt appearing
• “No bootable device” error
• Boot loops back to BIOS repeatedly
• Kernel panic messages like VFS: Unable to mount root fs

These usually point to a bootloader (GRUB), partition, or filesystem issue.

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🔧 Step 1 — Boot from a Live USB

1. Create an Ubuntu Live USB using Rufus, balenaEtcher, or dd:

# Example using dd (Linux/macOS)
sudo dd if=ubuntu-24.04-desktop-amd64.iso of=/dev/sdX bs=4M status=progress
sync
# Replace /dev/sdX with your USB device (NOT a partition like /dev/sdX1)

1. Boot the affected machine from the USB and choose Try Ubuntu.

2. Open a terminal (Ctrl+Alt+T) in the live session.

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🧭 Step 2 — Identify your partitions

Find the Linux root partition and the EFI partition (if present):

sudo fdisk -l

Look for lines indicating a Linux filesystem (usually the root /) and an EFI System partition (FAT32, ~100–500MB). Example:

/dev/sda1   *   EFI System
/dev/sda2       Boot partition
/dev/sda3       Linux filesystem

Note: On NVMe devices the names look like /dev/nvme0n1p1, /dev/nvme0n1p2.

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🧱 Step 3 — Mount and chroot into your system

This lets you run commands as if you booted into the installed system.

sudo mount /dev/sda2 /mnt                     # mount root (replace with your root partition)
sudo mount /dev/sda1 /mnt/boot/efi            # mount EFI if using UEFI (skip for BIOS)
for i in /dev /dev/pts /proc /sys /run; do sudo mount --bind "$i" "/mnt$i"; done      #This is very usefull for quick mounting
sudo chroot /mnt
# You are now inside the installed system as root

If your root is on LVM or encrypted, adapt mounting steps (activate volume groups or unlock LUKS first).

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⚙️ Step 4 — Reinstall / Repair GRUB

If the system boots with UEFI, reinstall GRUB for EFI:

grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=ubuntu
update-grub

For legacy BIOS (MBR):

grub-install /dev/sda   # install to the disk, not a partition
update-grub

You should see output showing detected kernels (e.g. /boot/vmlinuz-...).

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🔧 Step 5 — Exit chroot and unmount cleanly

exit
for i in /run /sys /proc /dev/pts /dev; do sudo umount "/mnt$i" || true; done
sudo umount /mnt/boot/efi || true   # only if you mounted it earlier
sudo umount /mnt || true
sync
sudo reboot

If the system still doesn’t boot, collect logs and try the alternative steps below.

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🛠️ Additional recovery steps

• Check filesystem integrity (run from live session or chroot):

sudo fsck -fy /dev/sda2   # replace with your filesystem device

• Inspect dmesg and /var/log/boot.log (or journalctl -xb) for kernel/driver errors.

• If GRUB is present but cannot find kernels, verify /boot contents and that update-grub detected kernels.

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🚑 Use Boot-Repair (GUI helper)

Boot-Repair is a graphical tool that automates many fixes (useful for less-experienced users):

1. From the live session, add Boot-Repair PPA and install:

sudo add-apt-repository ppa:yannubuntu/boot-repair -y
sudo apt update
sudo apt install -y boot-repair
boot-repair

1. Choose Recommended repair and follow prompts. Boot-Repair will attempt to reinstall GRUB and fix common issues.

Note: Review the Boot-Repair URL it prints — it contains a diagnostic summary you can share for help.

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🧾 Troubleshooting tips & notes

• Always double-check device names (/dev/sda, /dev/nvme0n1) before running destructive commands.
• If you use full-disk encryption or LVM, unlock and activate volumes before mounting.
• For UEFI systems, ensure the firmware is set to boot the correct EFI entry (check efibootmgr -v).
• If GRUB is installed but system drops to grub> or grub rescue>, use GRUB commands to boot manually or reinstall from chroot.

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✅ When to ask for help

If you’re stuck, collect the following and share when requesting help on forums:

• Output of sudo fdisk -l or lsblk -f
• Contents of /boot and /boot/efi (if present)
• sudo efibootmgr -v (for UEFI systems)
• Any error text shown at boot (take photos if needed)

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