sudo apt-get install mysql-server-4.1 mysql-common-4.1 \
    mysql-client-4.1 libmysqlclient14-dev libmysqlclient14 \
    mytop zlib1g-dev


ruby --version
ruby 1.8.5 (2006-08-25) [i486-linux]


sudo apt-get install libmysql-ruby1.8


echo "require 'mysql'" | irb
require 'mysql'
true


irb
irb(main):002:0> require 'mysql'
=> true
irb(main):003:0> conn = Mysql.connect 'localhost','myusername','mypassword'
=> #<Mysql:0xb7f26c5c>
irb(main):004:0> conn.server_info
=> "4.1.11-Debian_4sarge7-log"
irb(main):006:0> conn.list_dbs
=> ["testapp_dev", "testapp_production", "testapp_test", "mysql", "test"]
irb(main):007:0> conn.ping
=> #<Mysql:0xb7f26c5c>
irb(main):008:0> conn.select_db 'testapp_production'
=> #<Mysql:0xb7f26c5c>
irb(main):009:0> conn.list_tables
=> []
irb(main):010:0> conn.stat
=> "Uptime: 51776  Threads: 1  Questions: 35  Slow queries: 0  Opens: 26  Flush tables: 1  Open tables: 15  Queries per second avg: 0.001"
irb(main):011:0>



script/console
Loading development environment.
./script/../config/../config/../vendor/rails/activerecord/lib/active_record/
connection_adapters/mysql_adapter.rb:6:in `define_all_hashes_method!':
RuntimeError: Mysql not loaded
>>


#database.yml
#development:
#  adapter: mysql
#  database: testapp_dev
#  host: localhost
#  encoding: utf8
#  username: myusername
#  password: mypassword
#
#test:
#  adapter: mysql
#  database: testapp_test
#  host: localhost
#  encoding: utf8
#  username: myusername
#  password: mypassword
#
#production:
#  adapter: mysql
#  database: testapp_production
#  host: localhost
#  encoding: utf8
#  username: myusername
#  password: mypassword

Looking at:

less vendor/rails/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
require 'active_record/connection_adapters/abstract_adapter'

module MysqlCompat
  # add all_hashes method to standard mysql-c bindings or pure ruby version
  def self.define_all_hashes_method!
    raise 'Mysql not loaded' unless defined?(::Mysql::Result)
...

then back in irb:

irb
irb(main):001:0> require 'mysql'
=> true
irb(main):002:0> puts "true" if defined? ::Mysql::Result
=> nil
irb(main):003:0> puts "true" if defined? ::Mysql
true
=> nil
irb(main):004:0> puts "true" if defined? ::Mysql::Result
=> nil