The error occurs while installing RAC software and already an existing single instance oracle restart is present on the host which prevents the installation
Cause - The installer detected single-instance versions of Cluster Synchronization Services (CSS) on the following nodes in the cluster:exdbadm02 Action - Before proceeding with the installation, you must deconfigure CSS, shut down any Oracle Automatic Storage Management (Oracle ASM) instances, and shut down all databases that use Oracle ASM for storage on all of the listed nodes. Oracle Clusterware installation starts a cluster-wide version of CSS. After Oracle Clusterware installation is complete, you may start up any databases and Oracle ASM instances that previously used CSS. When they are brought back up, Oracle Clusterware provides CSS.
Check the single instance oracle restart configuration on the server
[root@exdbadm02 oracle]# ps -ef|grep has root 4198 1 0 16:59 ? 00:00:00 /bin/sh /etc/init.d/init.ohasd run root 7046 5418 0 17:25 pts/6 00:00:00 grep has
Deconfigure the existing configuration of has
[root@exdbadm02 install]# ./roothas.pl -deconfig -force
Deinstall the grid software
[oracle@exdbadm02 deinstall]$ ./deinstall Checking for required files and bootstrapping ... Please wait ...
Now proceed to install RAC