Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

last week I installed and successfully set up mysql on mac… (10.6.6)
was able to connect fine from unix shell and from PHP and JSP… today, just a week later, I can’t connect with either PHP or JSP, and when try to connect from unix shell I get this error:

Can’t connect to local MySQL server through socket ‘/tmp/mysql.sock’ (2)

what is this please… would appreciate some help…

thank you…