解决drush PDOException: SQLSTATE[HY000] [2002]问题的办法分析

Drush command terminated abnormally due to an unrecoverable error. [error] 
<h1>Additional uncaught exception thrown while handling exception.</h1> 
<h2>Original</h2> 
<p>PDOException: SQLSTATE[HY000] [2002] No such file or directory in drupal_is_denied() 
(line 1915 of /Applications/rubystack/apps/drupal/htdocs/includes/bootstrap.inc).</p> 
<h2>Additional</h2> 
<p>PDOException: SQLSTATE[HY000] [2002] No such file or directory in system_list() 
(line 165 of /Applications/rubystack/apps/drupal/htdocs/includes/module.inc).</p><hr />
Process finished with exit code 1 at 17:04:06. 
Execution time: 221 ms.

array (
'database' => 'demo_drupal',
'username' => 'root',
'password' => '',
'host' => 'localhost',
'port' => '3309',
'unix_socket' => '/Applications/rubystack/mysql/tmp/mysql.sock',
'driver' => 'mysql',
'prefix' => '',
)

lixideMacBook-Pro:htdocs lixi$ /Users/lixi/drush/drush status 
Drupal version                  :  7.25 
Site URI                        :  http://default 
Database driver                 :  mysql 
Database username               :  root 
Database name                   :  demo_drupal 
Database                        :  Connected 
Drupal bootstrap                :  Successful 
Drupal user                     : 
Default theme                   :  bartik 
Administration theme            :  seven 
PHP executable                  :  /usr/bin/php 
PHP configuration               : 
PHP OS                          :  Darwin 
Drush version                   :  7.0-dev 
Drush configuration             : 
Drush alias files               : 
Drupal root                     :  /Applications/rubystack/apps/drupal/htdocs 
Site path                       :  sites/default 
File directory path             :  sites/default/files 
Temporary file directory path   :  /Applications/rubystack/php/tmp

lixideMacBook-Pro:htdocs lixi$ /Users/lixi/drush/drush up 
Name Installed Version Proposed version Message 
Drupal 7.25 7.26 SECURITY UPDATE available
Update information last refreshed: Sun, 01/19/2014 – 13:58 
Code updates will be made to drupal core. 
WARNING: Updating core will discard any modifications made to Drupal core files, 
most noteworthy among these are .htaccess and robots.txt. 
If you have made any modifications to these files, 
please back them up before updating so that you can re-create your modifications in the 
updated version of the file. 
Note: Updating core can potentially break your site. 
It is NOT recommended to update production sites without prior testing.
Do you really want to continue? (y/n): y 
Project drupal was updated successfully. Installed version is now 7.26. 
Backups were saved into the directory [ok] 
/Users/lixi/drush-backups/bitnami_drupal7/20140120095445/drupal. 
Taxonomy 7011 Drop unpublished nodes from the index. 
Do you wish to run all pending updates? (y/n): y 
Performed update: taxonomy_update_7011 [ok] 
‘all’ cache was cleared. [success] 
Finished performing updates. [ok]