connect mysql server and dump current database schema

1.modify database.yml to configure database connection
#vim config/database.yml
modify content like this
development:
adapter: mysql
encoding: utf8
database: cms_development
pool: 5
username: root
password: abc123
timeout: 5000

test:
adapter: mysql
encoding: utf8
database: cms_test
pool: 5
username: root
password: abc123
timeout: 5000

production:
adapter: mysql
encoding: utf8
database: cms_production
pool: 5
username: root
password: abc123
timeout: 5000

2.use rake to dump current migration
#rake db:schema:dump
it will generate schema.db on db folder