Run the following commands on all three nodes in the cluster (nodes are named f1, f2 and f3). This will create the corosync.conf files for the cluster.
[root@f1 pcs]# ./pcs cluster configure my_cluster_name f1 f2 f3
[root@f2 pcs]# ./pcs cluster configure my_cluster_name f1 f2 f3
[root@f3 pcs]# ./pcs cluster configure my_cluster_name f1 f2 f3
Then run the following command on all three nodes in the cluster, to start corosync and pacemaker.
[root@f1 pcs]# ./pcs cluster start
Starting Cluster