Rollback Ambari to 2.6.5

You must use the backup of Ambari 2.6.x to perform the following steps.

Stop all services in Ambari UI.

On the Ambari Server host, stop the Ambari Server.

ambari-server stop
Stop  Ambari Agent on all host
ambari-agent stop

Obtain Ambari Repositories:

wget -nv 
https://archive.cloudera.com/p/ambari/2.x/${your_ambari_version}/centos7/ambari.repo -O 
/etc/yum.repos.d/ambari.repo
yum clean all

Downgrade ambari-server, ambari-agent packages manually using “yum downgrade <packagename>”
```
yum  downgrade ambari-server
yum  downgrade ambari-agent # on all hosts
```

Reinitialize Ambari DB - Drop the old schema and initialize blank new schema :

Example - Postgres

psql -W -d ${AMBARI_DB_NAME} --user ${AMBARI_DB_USER}
DROP SCHEMA ${AMBARI_DB_NAME} CASCADE;
CREATE SCHEMA ambari;
GRANT ALL ON SCHEMA ambari TO ambari;

MYSQL

mysql -u ${AMBARI_DB_USER} 
drop database ${AMBARI_DB_NAME}; 
create database ${AMBARI_DB_NAME};

Populate the Ambari database with backup data:

POSTGRES

psql -W -d ${AMBARI_DB_NAME} --user ${AMBARI_DB_USER} < pre_upgrade.sql

MYSQL

mysql -u ${AMBARI_DB_USER} ${AMBARI_DB_NAME} < pre_upgrade.sql

Clear views cache (it has views for 7.1 cached, some of which are not supported):
```
rm -f /var/lib/ambari-server/resources/views/work/*
```

Restore these files from the backup:

/etc/ambari-server/conf/ambari.properties
/etc/ambari-agent/conf/ambari-agent.ini

Restore old stack symlinks on Agent nodes:
```
hdp-select set all 2.6.5.0-292
```
Check ambari-server user:
```
grep ambari-server.user /etc/ambari-server/conf/ambari.properties
```
If ambari-server is running as non-root user, set permissions for files by running: ambari-server setup
Start Ambari