Need help : pgsql HA issues

Hello All,

We are in process of testing a Postgres 9.6 active-passive HA cluster using streaming replication on Rhel 7.5.

We are seeing below issue with the setup :

1. When a failover is triggered  while data is being added to the primary by killing primary (killall -9 postgres), the failed node is restarted to but doesn't start streaming. It starts in disconnect mode. We checked and notice that the wal receiver process is not started. Need help in

1. To check why the wal receiver process is not stated ? Is killed -9 leaving some processes uncleaned because of which the walk receiver is not starting ?

2. How can we simulate abrupt shut down of postgresql ? We want to simulate case where primary goes down abruptly

Please share any pointers if you have.

Thanks