Stop redis server. Neither shutdown nor stop works

Question

I want to stop the redis server and it just keeps going and going. I am using redis-2.6.7

Check that it is running:

redis-server

It say

Answer 1

redis-cli -a password shutdown

or

ps aux|grep redis
kill -9 

The above solutions doesn't work. The redis server will restart with a new pid. But the below command works.

/etc/init.d/redis-server stop

My server is Ubuntu 18.04.2 and Redis version is v4.0.9