Apache Kafka : start up scripts

Dear Kafka experts

when an broker is started using start script , could any of you please let
me know the sequence of steps that happens in the back ground when the node
UP

like : when the script is initiated to start ,
1/ is it checking indexes .. ?
2/ is it checking isr ?
3/ is URP being made to zero.. ?

i tried to look in ther server log but could not under the sequence of
events performed till the node was up .. could some one please help ..

Thanks