CentOS 6 Fix : Cannot find a valid baseurl for repo: base

To solve the error, follow the steps below on the command screen.

1. sed -i -e 's/mirror.centos.org/vault.centos.org/g' /etc/yum.repos.d/CentOS-Base.repo
2. sed -i -e 's/#baseurl/baseurl/g' /etc/yum.repos.d/CentOS-Base.repo
3. yum clean all
4. yum update -y