##src: https://www.digitalocean.com/community/tutorials/how-to-set-up-master-slave-replication-on-postgresql-on-an-ubuntu-12-04-vps#configure-the-master-server

############## Master:

psql -c "CREATE USER rep REPLICATION LOGIN CONNECTION LIMIT 1 ENCRYPTED PASSWORD 'yourpassword';"

#//at file /etc/postgresql/9.5/main/pg_hba.conf 

	host    replication     rep     IP_address_of_slave/32   md5

#//at file /etc/postgresql/9.5/main/postgresql.conf

	listen_addresses = 'localhost,IP_address_of_THIS_host'
	wal_level = 'hot_standby'
	archive_mode = on
	archive_command = 'cd .'
	max_wal_senders = 1
	hot_standby = on

service postgresql restart


############### Slave:

service postgresql stop

#//at file /etc/postgresql/9.5/main/pg_hba.conf 

	host    replication     rep     IP_address_of_master/32  md5

#//at file /etc/postgresql/9.5/main/postgresql.conf

	listen_addresses = 'localhost,IP_address_of_THIS_host'
	wal_level = 'hot_standby'
	archive_mode = on
	archive_command = 'cd .'
	max_wal_senders = 1
	hot_standby = on


################## Master:

psql -c "select pg_start_backup('initial_backup');"
rsync -cva --inplace --exclude=*pg_xlog* /var/lib/postgresql/9.5/main/ slave_IP_address:/var/lib/postgresql/9.5/main/
psql -c "select pg_stop_backup();"


################### Slave:

cd /var/lib/postgresql/9.5/main/recovery.conf

	standby_mode = 'on'
	primary_conninfo = 'host=master_IP_address port=5432 user=rep password=yourpassword'
	trigger_file = '/tmp/postgresql.trigger.5432' ##When we want to set SLAVE db to Master (because of original MASTER fail) creating this file is enough. With the existence of this file db will act like MASTER.

service postgresql start

## we check if no problem:

less /var/log/postgresql/postgresql-9.5-main.log