protocol.rb:212:in `initialize': No such file or directory - /tmp/mysql.sock

Ruby mysql error

===================
chang@cm-test:/aost$ ruby gen_pot.rb
/usr/local/lib/ruby/gems/1.9.1/gems/ruby-mysql-2.9.4/lib/mysql/protocol.rb:212:in `initialize': No such file or directory - /tmp/mysql.sock (Errno::ENOENT)
from /usr/local/lib/ruby/gems/1.9.1/gems/ruby-mysql-2.9.4/lib/mysql/protocol.rb:212:in `new'
from /usr/local/lib/ruby/gems/1.9.1/gems/ruby-mysql-2.9.4/lib/mysql/protocol.rb:212:in `block in initialize'
from /usr/local/lib/ruby/1.9.1/timeout.rb:44:in `timeout'
from /usr/local/lib/ruby/gems/1.9.1/gems/ruby-mysql-2.9.4/lib/mysql/protocol.rb:209:in `initialize'
from /usr/local/lib/ruby/gems/1.9.1/gems/ruby-mysql-2.9.4/lib/mysql.rb:110:in `new'
from /usr/local/lib/ruby/gems/1.9.1/gems/ruby-mysql-2.9.4/lib/mysql.rb:110:in `connect'
from /usr/local/lib/ruby/gems/1.9.1/gems/ruby-mysql-2.9.4/lib/mysql.rb:42:in `new'
from gen_blogspot.rb:9:in `

'
chang@cm-test:/opt/pubchem/ruby/autopost$ ^C


solution:
1, install
sudo apt-get install libmysqlclient15-dev

2
reinstall mysql gem
sudo gem install mysql