database.yml, mysql and ubuntu

If you don't want to specify 'socket' entry in rails database.yml simply create link for it:

sudo ln -s /var/run/mysqld/mysqld.sock /tmp/mysql.sock

Now you database.yml may look like this:

defaults: &defaults
  adapter: mysql
  encoding: utf8
  username: user
  password: secret
  host: localhost

development:
  database: somedb
  <<: *defaults

test:
  database: somedb_test
  <<: *defaults

production:
  database: somedb_production
  <<: *defaults