Upgrade Your Linux Kernel on CentOS 7 and Ubuntu 16.04 in Simple Steps

1. Upgrade Kernel on CentOS 7

1.1 Check Installed Kernel Version

To display the currently installed kernel version, run:

# uname -sr
Linux 3.10.0-862.el7.x86_64

The latest kernel on kernel.org at the time of writing is 5.12. Consider the kernel lifecycle when choosing a version.

1.2 Upgrade Kernel

CentOS can use the third‑party ELRepo repository to obtain newer kernels. Enable ELRepo with:

# Import ELRepo public key
rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
# Install ELRepo yum repository
rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-3.el7.elrepo.noarch.rpm

1.3 List Available Kernel Packages

After enabling the repository, list the kernel packages you can install:

yum --disablerepo="*" --enablerepo="elrepo-kernel" list available

1.4 Install Latest Kernel

For CentOS, using yum to install the RPM avoids many dependency issues. By default it installs the newest kernel version available in ELRepo.

# Install the mainline kernel from ELRepo
yum -y --enablerepo=elrepo-kernel install kernel-ml

1.5 Set GRUB Default Kernel Version

After installation, set the new kernel as the default boot entry.

List All Available Kernels

# sudo awk -F' ' '$1=="menuentry " {print i++ ": " $2}' /etc/grub2.cfg
0 : CentOS Linux 7 Rescue 8916e15095f33283a3b46d8f9ac7c654 (5.12.1-1.el7.elrepo.x86_64)
1 : CentOS Linux (5.12.1-1.el7.elrepo.x86_64) 7 (Core)
2 : CentOS Linux (3.10.0-862.el7.x86_64) 7 (Core)
3 : CentOS Linux (0-rescue-ea3169a040da42e0b632f72ceb5abd82) 7 (Core)

Set New Kernel as GRUB Default

Use grub2-set-default 0 or edit /etc/default/grub to set the default entry.

# Set GRUB_DEFAULT=0 so the first entry becomes the default
grub2-set-default 0

Generate GRUB Config and Reboot

# Recreate GRUB configuration file
grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.12.1-1.el7.elrepo.x86_64
Found initrd image: /boot/initramfs-5.12.1-1.el7.elrepo.x86_64.img
Found linux image: /boot/vmlinuz-3.10.0-862.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-862.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-8916e15095f33283a3b46d8f9ac7c654
Found initrd image: /boot/initramfs-0-rescue-8916e15095f33283a3b46d8f9ac7c654.img
Found linux image: /boot/vmlinuz-0-rescue-ea3169a040da42e0b632f72ceb5abd82
Found initrd image: /boot/initramfs-0-rescue-ea3169a040da42e0b632f72ceb5abd82.img
done

Verify

# reboot
# uname -r
5.12.1-1.el7.elrepo.x86_64

Upgrade successful.

Side Note

Creating Offline Kernel Upgrade Packages Without Internet

# Install tools for creating a repository
yum -y install yum-utils
yum -y install createrepo
# Download required packages (example for httpd)
repotrack httpd -p ./httpds/   # or yumdownloader --resolve --destdir /tmp/ansible ansible
# Create offline kernel package directory
repotrack kernel-ml.x86_64 -p ./kernel-ml.x86_64/   # or yumdownloader --resolve --destdir ./kernel-ml.x86_64 kernel-ml.x86_64
# Copy the ./kernel-ml.x86_64 directory to the target machine and install

Remove Old Kernels

List all installed kernel packages:

# rpm -qa | grep kernel
kernel-headers-3.10.0-957.27.2.el7.x86_64
kernel-tools-3.10.0-862.el7.x86_64
kernel-debug-devel-3.10.0-957.27.2.el7.x86_64
kernel-ml-5.12.1-1.el7.elrepo.x86_64
kernel-3.10.0-862.el7.x86_64
kernel-tools-libs-3.10.0-862.el7.x86_64

Method 1: remove specific old kernel RPMs with yum remove. Method 2: use yum-utils to clean up old kernels automatically when more than three are installed:

# yum install -y yum-utils
# package-cleanup --oldkernels

2. Upgrade Kernel on Ubuntu

2.1 Environment

On an Ubuntu 16.04 VM, check the current kernel version with uname -r. The current version is 4.15.0-45-generic; the target version is 4.20.2.

2.2 Prepare Required Packages

Download the desired kernel version from kernel.ubuntu.com . Choose the appropriate amd64 .deb files and download them:

wget https://kernel.ubuntu.com/~kernel-ppa/mainline/v4.20.5/linux-headers-4.20.5-042005_4.20.5-042005.201901260434_all.deb
wget https://kernel.ubuntu.com/~kernel-ppa/mainline/v4.20.5/linux-headers-4.20.5-042005-generic_4.20.5-042005.201901260434_amd64.deb
wget https://kernel.ubuntu.com/~kernel-ppa/mainline/v4.20.5/linux-image-unsigned-4.20.5-042005-generic_4.20.5-042005.201901260434_amd64.deb
wget https://kernel.ubuntu.com/~kernel-ppa/mainline/v4.20.5/linux-modules-4.20.5-042005-generic_4.20.5-042005.201901260434_amd64.deb

2.3 Install

Install the downloaded .deb packages with dpkg: sudo dpkg -i *.deb Reboot the system and verify the new kernel:

# reboot
# uname -r
Linux hadoop-master02 4.20.5-042005-generic

Kernel upgrade successful.

2.4 Issues and Solutions

During the Ubuntu 16.04 kernel upgrade, a missing libssl1.1 dependency may occur.

Solution: install the libssl1.1 package from the official Ubuntu repositories or download the .deb manually and install it.

wget http://archive.ubuntu.com/ubuntu/pool/main/o/openssl/libssl1.1_1.1.0g-2ubuntu4_amd64.deb
dpkg -i libssl1.1_1.1.0g-2ubuntu4_amd64.deb