DOWNGRADING CENTOS 6.9 TO 6.8

We all are familier with updating our os.But what about downgrading...Its little risky..right?...Let me explain you about it..

1.First we need to downgrade the kernel.Here we want to downgrade from Centos 6.9 to 6.8

Find out kernel version running on centos 6.8. I found it as kernel-2.6.32-642.15.1.el6

# curl -O http://vault.centos.org/6.8/updates/x86_64/Packages/kernel-2.6.32-642.15.1.el6.x86_64.rpm

( ie, downloading the required kernel version)

#yum install kernel-2.6.32-642.15.1.el6.x86_64.rpm

(install the kernel version)

2. Now find the kernels present in grub

grep '^[[:space:]]*kernel' /boot/grub/grub.conf

From the list, identify the kernel that you want to set as default. Each kernel in the list is assigned by GRUB a numeric entry value starting from 0 in an increasing order. That is, the first entry assigned 0, the second entry assigned 1, etc.

Open /boot/grub/grub.conf with a text editor, and set GRUB_DEFAULT to the numeric entry value for the kernel you chose as the default. In this example, I choose the kernel 2.6.32-642 as the default kernel.

# vi /boot/grub/grub.conf

default=0

3.Now we want to make changes in our Centos-Vault.repo.Here we want to enable all entries for Centos 6.8

#vi /etc/yum.repos.d/CentOS-Vault.repo

[C6.8-base]

name=CentOS-6.8 - Base

baseurl=http://vault.centos.org/6.8/os/$basearch/

gpgcheck=1