@Raju Jha
Refer to the Ambari Docs to find the ambari repo URL based on the version of ambari that you want to install and the OS.
For CentOS6.9 you will need to choose Centos6 repo for (For RHEL/CentOS/Oracle Linux 6).
https://docs.hortonworks.com/HDPDocuments/Ambari-2.6.2.0/bk_ambari-installation/content/download_the...
Please choose the correct version of Ambari Doc (latest ambari version is Ambari 2.7.1)
.
For Example: If you want to install Ambari 2.6.2.0 then do this:
# wget -nv http://public-repo-1.hortonworks.com/ambari/centos6/2.x/updates/2.6.2.0/ambari.repo -O /etc/yum.repos.d/ambari.repo
# yum install ambari-server -y
# ambari-server setup -s
# ambari-server start
