bash-4.1$ rake db:migrate
(in /home/jrojas/rnii-ve)
rake aborted!
Please install the postgresql adapter: `gem install activerecord-postgresql-adapter` (no such file to load -- pg)

(See full trace by running task with --trace)
bash-4.1$ gem install activerecord-postgresql-adapter
ERROR:  Could not find a valid gem 'activerecord-postgresql-adapter' (>= 0) in any repository
ERROR:  Possible alternatives: activerecord-postgis-adapter, activerecord-jdbcpostgresql-adapter, activerecord-postgresql-cursors, activerecord-jdbcmysql-adapter, activerecord-jdbcmssql-adapter