1. Edit pg_hba.conf to enable replication connections.
2. Edit postgresql.conf to turn on the various replication options.
3. Restart the master.
4. Set up passwordless access to the master from the first replica and second replica.
5. Use rsync backup and send it to slave server
6. Create a recovery.conf pointing at the master.
7. Edit second slave recovery.conf to point at the first replica.
8. Start the first replica then.
9. Start the second replica.
More Info :https://www.tutorialdba.com/2018/03/how-to-configure-cascade-replication-on.html