Overview

The default kernel shipped with CentOS 7 and CentOS 8 is often older then what modern applications require. This guide covers two methods for upgrading the Linux kernel: using the ELRepo repository package manager, or manually installing RPM packages.

Warning: Kernel upgrades require careful consideration. The kernel is the core of the operating system, managing process scheduling, memory allocation, device drivers, and system calls.

Understanding Kernel Packages

Several kernel-related packages exist in CentOS:

• kernel: Core kernel for single-core, multi-core, and multi-processor systems
• kernel-devel: Headers and makefiles for building kernel modules
• kernel-headers: C header files for kernel-user space interface
• kernel-tools: Utilities for kernel manipulation
• perf: Performance monitoring tools
• linux-firmware: Device firmware files

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Method 1: Using yum/dnf Package Manager

Adding the ELRepo Repository

The ELRepo repository provides newer kernel versions not available in default repositories.

# For CentOS 8
sudo dnf -y install https://www.elrepo.org/elrepo-release-8.el8.elrepo.noarch.rpm

# For CentOS 7
sudo yum -y install https://www.elrepo.org/elrepo-release-7.el7.elrepo.noarch.rpm

Verifying Repository Installation

cat /etc/yum.repos.d/elrepo.repo

Importing GPG Key

sudo rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org

Listing Availbale Kernels

Mainline (latest stable) kernels:

dnf --disablerepo="*" --enablerepo="elrepo-kernel" list available | grep kernel-ml

Long-term support (LTS) kernels:

dnf --disablerepo="*" --enablerepo="elrepo-kernel" list available | grep kernel-lt

Installing the New Kernel

# Install mainline kernel
sudo dnf --enablerepo=elrepo-kernel install kernel-ml

# Or install LTS kernel
sudo dnf --enablerepo=elrepo-kernel install kernel-lt

Installing additional kernel development packages:

# For mainline
dnf --allowerasing --enablerepo=elrepo-kernel install kernel-ml-{devel,headers}


# For LTS
dnf --allowerasing --enablerepo=elrepo-kernel install kernel-lt-{devel,headers}

The --allowerasing flag removes conflicting older packages.

Configuring Default Boot Kernel

CentOS 8 Configuration

# List all available kernels
grubby --info=ALL | grep ^kernel

# Check current default kernel
grubby --default-kernel

# Set new default kernel (replace with your version)
grubby --set-default "/boot/vmlinuz-6.10.4-1.el8.elrepo.x86_64"

# Reboot system
reboot

CentOS 7 Configuration

# View boot menu order
awk -F\' '$1=="menuentry " {print $2}' /etc/grub2.cfg

# Set default boot entry (replace N with entry index)
grub2-set-default N

# Example: set first entry as default
grub2-set-default 0

# Reboot system
reboot

# Verify kernel version
uname -r

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Method 2: Manual RPM Installation

This method is useful when installing specific older kernel versions not available in ELRepo.

Locating Kernel RPMs

Download archives for CentOS 7 and 8:

• CentOS 7: https://mirrors.coreix.net/elrepo-archive-archive/kernel/el7/x86_64/RPMS/
• CentOS 8: https://mirrors.coreix.net/elrepo-archive-archive/kernel/el8/x86_64/RPMS/

Downloading Required Packages

Three packages are required: the main kernel, development headers, and standard headers.

wget https://mirrors.coreix.net/elrepo-archive-archive/kernel/el7/x86_64/RPMS/kernel-lt-5.4.274-1.el7.elrepo.x86_64.rpm
wget https://mirrors.coreix.net/elrepo-archive-archive/kernel/el7/x86_64/RPMS/kernel-lt-devel-5.4.274-1.el7.elrepo.x86_64.rpm
wget https://mirrors.coreix.net/elrepo-archive-archive/kernel/el7/x86_64/RPMS/kernel-lt-headers-5.4.274-1.el7.elrepo.x86_64.rpm

Installing the Packages

sudo rpm -ivh kernel-lt-5.4.274-1.el7.elrepo.x86_64.rpm
sudo rpm -ivh kernel-lt-devel-5.4.274-1.el7.elrepo.x86_64.rpm

Verifying Installation

rpm -qa | grep kernel

Expected output includes entries like:

• kernel-lt-5.4.274-1.el7.elrepo.x86_64
• kernel-lt-devel-5.4.274-1.el7.elrepo.x86_64

Setting Boot Configuration

For CentOS 7:

# View available boot entries
awk -F\' '$1=="menuentry " {print $2}' /etc/grub2.cfg

# Set default entry (index starts at 0)
grub2-set-default 0

# Reboot and verify
reboot
uname -r

For CentOS 8:

# View all kernels
grubby --info=ALL | grep ^kernel

# Check current default
grubby --default-kernel

# Set specific kernel as default
grubby --set-default "/boot/vmlinuz-6.10.4-1.el8.elrepo.x86_64"

# Reboot
reboot