Our startup and shutdown procedure is extensive. The relevant code lives in the following directories:

• src/mongo/base
• src/mongo/db
• src/mongo/db/commands
• src/mongo/s
• src/mongo/s/commands
• src/mongo/util

There are several important topics:

• Exit helper functions.
• The shutdown commands for both mongod and mongos.
• Program mains for both mongod and mongos.
• The MONGO_INITIALIZER subsystem.

Since this spans multiple directories, we should add a new markdown file in docs/.

This is intended to be abstract documentation, describe relationships and state transitions not code in common language.