Getting a mysql 2002 error only when using localhost (rather than 127.0.0.1) when connecting to mysql with php

Question

I have the following php file:

<?php
function show_error($stage) {
    echo "<p>MySql error: " . mysql_error() . '</p>';
    echo "<p>ErrorCode: " . mysql_errno() . '</p>';
    die($stage);

}

$link = mysql_connect('localhost', 'blog', 'sql-password');
if (!$link) {
    show_error('connect');
}
mysql_select_db('blog') or show_error();
$result = mysql_query('select col1 from test_table');
if (!$result) {
    show_error('query');
}
$col = mysql_result($result, 0);
echo "<p>Result is: [" . $col . "]</p>";
mysql_close($link);
?>

When I run this, I get error:

MySql error: No such file or directory

ErrorCode: 2002

connect

However, if I change the line

$link = mysql_connect('localhost', 'blog', 'my-password'); 

to

$link = mysql_connect('127.0.0.1', 'blog', 'my-password'); 

it all works correctly. How can I fix this so that it works with either localhost or 127.0.0.1 , and why does using localhost work differently to 127.0.0.1 ?

Extra info (some google responses indicated these were important):

• the line 127.0.0.1 localhost appears in my /etc/hosts file, and ping localhost works correctly, and hits the 127.0.0.1 address. There are no other lines mentioning localhost in the /etc/hosts file.
• I'm running it in Mac OSX Snow Leopard.

• Finally, the result of the command stat /tmp/mysql.sock is:

  234881044 28829652 srwxrwxrwx 1 _mysql wheel 0 0 "Jul 10 18:29:37 2011" "Jul 10 18:29:37 2011" "Jul 10 18:29:37 2011" "Jul 10 18:29:09 2011" 4096 0 0 /tmp/mysql.sock

Answer 1

The MySQL client magically knows that 'localhost' means the local machine, so it tries to connect to a Unix socket instead of making a network request--which is actually more efficient. The problem here is that you're either not using a Unix socket, or--probably more likely--the MySQL client libraries don't know where to find the Unix socket file.

I wish I could tell you where that configuration lives, but a) I haven't actively used MySQL in over 3 years, and b) I've never used MySQL on OSX.