How to Upgrade/Update Kernel in Redhat Enterprise Linux 6 (RHEL6)

In this post we will see how to update KERNEL package. As a system administrator you may require to upgrade kernel package. Upgrading kernel package is necessary for adding new features, resolving security related issues, etc. Kernel upgrade can cause problems if other packages depend on current kernel version.

If you are interested in new kernel, never use -U option as this overwrites the existing kernel and it would be hard to revert the changes. The best option to upgrade a kernel is to install new one.

You can install new kernel package using below mentioned command in Redhat Enterprise Linux 6 (RHEL6).

Linux Kernel Architecture.

# rpm -ivh new_kernel.rpm

Above command install new kernel, and related files, along with the old one.

In the below example we will upgrade kernel from 2.6.32-220.el6.x86_64 to 2.6.32-220.2.1.el6.x86_64:

To see the current kernel version:

# uname -r
2.6.32-220.el6.x86_64

Download new kernel package and install:

# rpm -ivh kernel-2.6.32-220.2.1.el6.x86_64.rpm

warning: kernel-2.6.32-220.2.1.el6.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID fd431d51: NOKEY

Preparing...               ########################################### [100%
1:kernel                   ########################################### [100%]

To verify the new kernel is installed, list contents of /boot directory:

# ls /boot/

config-2.6.32-220.2.1.el6.x86_64
config-2.6.32-220.el6.x86_64
efi
grub
initramfs-2.6.32-220.2.1.el6.x86_64.img
initramfs-2.6.32-220.el6.x86_64.img
lost+found
symvers-2.6.32-220.2.1.el6.x86_64.gz
symvers-2.6.32-220.el6.x86_64.gz
System.map-2.6.32-220.2.1.el6.x86_64
System.map-2.6.32-220.el6.x86_64
vmlinuz-2.6.32-220.2.1.el6.x86_64
vmlinuz-2.6.32-220.el6.x86_64

After installation of new kernel there will be an entry for new kernel in /etc/grub.conf (/boot/grub/grub.conf).

# cat /etc/grub.conf

# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /boot/, eg.
#          root (hd0,0)
#          kernel /vmlinuz-version ro root=/dev/mapper/OSVG-lvroot
#          initrd /initrd-[generic-]version.img
#boot=/dev/sda

default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux Server (2.6.32-220.2.1.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-220.2.1.el6.x86_64 ro root=/dev/mapper/OSVG-lvroot rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=OSVG/lvswap SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto quiet rd_LVM_LV=OSVG/lvroot  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM
        initrd /initramfs-2.6.32-220.2.1.el6.x86_64.img
        title Red Hat Enterprise Linux (2.6.32-220.el6.x86_64)

        root (hd0,0)
        kernel /vmlinuz-2.6.32-220.el6.x86_64 ro root=/dev/mapper/OSVG-lvroot rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=OSVG/lvswap SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto quiet rd_LVM_LV=OSVG/lvroot  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM
        initrd /initramfs-2.6.32-220.el6.x86_64.img

As you can see above that default kernel at boot time is 0 which is new kernel.
Reboot the server and check for the new kernel. If new kernel does not work you can change default option to 1, to boot form the old kernel.

After server restart verify the new kernel version.

# uname -r
2.6.32-220.2.1.el6.x86_64

# rpm -qa kernel
kernel-2.6.32-220.el6.x86_64
kernel-2.6.32-220.2.1.el6.x86_64

In the next post we will learn package management through YUM to automatically resolve dependencies.