PHP error happened

Technical information
Error type2
Error descriptionmysql_connect(): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)
URLwww.arb.ca.gov/ei/speciate/profilevrsn_list.php?
Error file/app/www/outside/ei/speciate/include/dbconnection.php
Error line9
SQL query