Drush was not able to start (bootstrap) the Drupal database. [error]
Hint: This may occur when Drush is trying to:* bootstrap a site that has not been installed or does not have a configured
database. In this case you can select another site with a working database setup
by specifying the URI to use with the --uri parameter on the command line. See
`drush topic docs-aliases` for details.
* connect the database through a socket. The socket file may be wrong or the
php-cli may have no access to it in a jailed shell. See
http://drupal.org/node/1428638 for details.
环境：centos 6.5 php 5.5 mysql 5.6 nginx 1.4.4