Rollback Ambari 7.1.x to Ambari 2.7.5

You must use the backup of Ambari 2.7.5 to perform the following steps.

In 7.1.x, x represents greater than or equal to 6. For example, 7.1.6, 7.1.7, and so on.

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

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 3.1.5.0-152
```
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