favoritism is the word of the day
You apply and interview
Difficult unless someone retires
Written test and oral board.
Seniority-based. Rare opportunities for promotion.
Not very easy
You only get promoted if you apply to another position with better pay.
There are no promotions. You apply for another job if you’re interested and compete with the public; or the senior leadership hires whoever they want into positions.
You apply alongside outside applicants. No special considerations.