how do i know if mysql/php/apache are installed
 

I am using a red hat linux distro and when ever i try to access the database i get this error msg.........
'cant connect to local Mysql server through socket "/var4/lib/mysql/mysql.sock" every time

I am now wondering that mysql is not installed or properly configured.

how do i know if mysql/php/apache are installed

To know if they're installed, well you can run the following on bash/terminal as root:

rpm -qa | grep -i mysql
rpm -qa | grep -i httpd
rpm -qa | grep -i php

Hope that helps