Omeka has encountered an error

Zend_Db_Adapter_Mysqli_Exception

Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (111)

exception 'Zend_Db_Adapter_Mysqli_Exception' with message 'Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (111)' in /var/www/clinton_omeka/application/libraries/Zend/Db/Adapter/Mysqli.php:340
Stack trace:
#0 /var/www/clinton_omeka/application/libraries/Zend/Db/Adapter/Abstract.php(316): Zend_Db_Adapter_Mysqli->_connect()
#1 /var/www/clinton_omeka/application/libraries/Omeka/Db.php(87): Zend_Db_Adapter_Abstract->getConnection()
#2 /var/www/clinton_omeka/application/libraries/Omeka/Db/Table.php(648): Omeka_Db->__call('query', Array)
#3 /var/www/clinton_omeka/application/libraries/Omeka/Db/Table.php(648): Omeka_Db->query(Object(Omeka_Db_Select), Array)
#4 /var/www/clinton_omeka/application/libraries/Omeka/Db/Table.php(429): Omeka_Db_Table->fetchObjects(Object(Omeka_Db_Select), Array)
#5 /var/www/clinton_omeka/plugins/SolrSearch/models/SolrSearchFieldTable.php(130): Omeka_Db_Table->findBySql('is_facet=?', Array)
#6 /var/www/clinton_omeka/plugins/SolrSearch/controllers/ResultsController.php(153): SolrSearchFieldTable->getActiveFacetKeys()
#7 /var/www/clinton_omeka/plugins/SolrSearch/controllers/ResultsController.php(94): SolrSearch_ResultsController->_getParameters()
#8 /var/www/clinton_omeka/plugins/SolrSearch/controllers/ResultsController.php(65): SolrSearch_ResultsController->_search(0, '500', true)
#9 /var/www/clinton_omeka/application/libraries/Zend/Controller/Action.php(516): SolrSearch_ResultsController->indexAction()
#10 /var/www/clinton_omeka/application/libraries/Zend/Controller/Dispatcher/Standard.php(308): Zend_Controller_Action->dispatch('indexAction')
#11 /var/www/clinton_omeka/application/libraries/Zend/Controller/Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#12 /var/www/clinton_omeka/application/libraries/Zend/Application/Bootstrap/Bootstrap.php(105): Zend_Controller_Front->dispatch()
#13 /var/www/clinton_omeka/application/libraries/Zend/Application.php(384): Zend_Application_Bootstrap_Bootstrap->run()
#14 /var/www/clinton_omeka/application/libraries/Omeka/Application.php(77): Zend_Application->run()
#15 /var/www/clinton_omeka/index.php(23): Omeka_Application->run()
#16 {main}