Unexpected system crashes, boot failures, or hardware issues often trace back to a recent Linux kernel update. Rolling back to a previous kernel using GRUB not only restores system functionality but also allows you to troubleshoot and resolve compatibility problems without waiting for upstream fixes. This process is crucial for administrators and users who need to keep systems operational, especially when newer kernels disrupt critical drivers or introduce regressions.

Booting Into a Previous Kernel Using GRUB

Step 1: Restart your computer and access the GRUB boot menu. On many distributions, holding the Shift key (for BIOS systems) or repeatedly pressing Esc (for UEFI systems) during boot displays the GRUB menu. Some distributions may hide this menu by default, requiring these keys to reveal it.

Step 2: Use the arrow keys to navigate to Advanced options for [Your Distro] and press Enter. This submenu lists all installed kernel versions alongside their respective recovery modes.

Step 3: Select the previous (older) kernel version that you know is stable. Avoid the recovery mode unless you specifically need it for troubleshooting. Press Enter to boot into the selected kernel.

Step 4: Confirm that your system boots successfully and verify that previous issues—such as driver incompatibility or system instability—are resolved with the older kernel.

Setting the Default Kernel in GRUB

If manually selecting the kernel at each boot is inconvenient, you can configure GRUB to automatically boot into your preferred kernel version by default. This ensures system stability across reboots without user intervention.

Step 1: Identify the menu entry number or name for your desired kernel. You can list them using:

sudo awk -F\' '$1=="menuentry " {print i++ " : " $2}' /boot/grub2/grub.cfg

This command outputs a numbered list of available boot entries. Note the index number corresponding to your preferred kernel.

Step 2: Set the default kernel by its index using:

sudo grub2-set-default

Replace <index-number> with the appropriate number from the previous step.

Step 3: Update the GRUB environment to confirm the default setting:

sudo grub2-editenv list

Step 4: Reboot your system. GRUB should now automatically boot into the selected kernel unless you manually choose another option.

Removing a Problematic Kernel

To prevent accidental booting into a faulty kernel, you may want to remove it from your system. This also helps free up space in the /boot partition, which is often limited.

On Debian, Ubuntu, and Derivatives

Step 1: List installed kernel images:

dpkg --list | grep linux-image

Step 2: Remove the unwanted kernel using:

sudo apt remove linux-image-<version>

Replace <version> with the exact version string from the previous list.

Step 3: Update GRUB to reflect the removal:

sudo update-grub

On Fedora, CentOS, and RHEL

Step 1: List installed kernels:

dnf list installed kernel

Step 2: Remove the problematic kernel:

sudo dnf remove kernel-<version>

Step 3: If residual files remain in /boot, remove them manually. For example:

sudo rm /boot/vmlinuz-<version> /boot/initramfs-<version>.img

Step 4: Rebuild the GRUB configuration if necessary:

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

Downgrading the Kernel Package

In cases where the desired kernel version is not currently installed, you may need to reinstall or downgrade the kernel package. This approach is especially useful if the previous kernel was removed or overwritten.

Debian/Ubuntu-Based Systems

Step 1: Search for available older kernel packages:

apt list --all-versions linux-image

Step 2: Install the specific older kernel package:

sudo apt install linux-image-<old-version>

Install matching headers if you use proprietary drivers:

sudo apt install linux-headers-<old-version>

Step 3: Update GRUB and reboot to select the restored kernel.

Fedora/CentOS/RHEL Systems

Step 1: Download the required kernel RPMs from the official archives or trusted sources. For Fedora, you can use the Koji build system to find older kernel packages.

Step 2: Install the downloaded RPMs:

sudo dnf install ./kernel-*.rpm

Step 3: Update GRUB as needed and reboot.

Arch Linux Systems

Step 1: Use the downgrade AUR script or manually download the older kernel from the Arch Linux Archive.

Step 2: Install the desired kernel version:

sudo pacman -U linux-<old-version>.pkg.tar.zst

Step 3: Add IgnorePkg = linux linux-headers to /etc/pacman.conf to prevent automatic upgrades.

Preventing Automatic Kernel Upgrades

Once you've rolled back to a stable kernel, you may want to prevent your package manager from automatically updating the kernel until the upstream issue is resolved.

  • On Debian/Ubuntu, use APT pinning by creating a file in /etc/apt/preferences.d/ specifying your desired kernel version and a high Pin-Priority.
  • On Fedora/CentOS, add exclude=kernel* to your /etc/dnf/dnf.conf or /etc/yum.conf.
  • On Arch Linux, add IgnorePkg = linux linux-headers to /etc/pacman.conf.

Remember to remove these restrictions when you are ready to test new kernel updates, as running outdated kernels for extended periods can expose your system to security vulnerabilities.

Troubleshooting and Best Practices

Boot failures after a kernel downgrade often result from mismatched kernel headers, missing drivers, or incorrect GRUB configurations. Always install matching kernel headers and modules when using proprietary drivers or virtualization tools. If your system becomes unbootable, use a live USB to mount your partitions, chroot into your installation, and repair kernel or GRUB settings.

Maintain at least one additional working kernel on your system for fallback. Back up important data before making kernel changes, and document each step to simplify future troubleshooting or rollbacks. When possible, use only official repositories or distribution archives to source kernel packages, minimizing the risk of introducing security or compatibility issues.

Rolling back your Linux kernel through GRUB restores system reliability when updates cause problems. With careful management of kernels and GRUB settings, you can quickly recover from most kernel-related disruptions and keep your system running smoothly.