PHP -MySQL:No connection could be made

I tried to connect mysql database.but am getting the following error.

Warning: mysql_connect(): [2002] No connection could be made because the target machine actively (trying to connect via tcp://localhost:3306) in test.php on line 5

Warning: mysql_connect(): No connection could be made because the target machine actively refused it. in test.php on line 5 Warning: mysql_close() expects parameter 1 to be resource, boolean given in test.php on line 15

test.php:

$link = mysql_connect(localhost, dbuser, dbpass);
if (!$link) {
   die('Could not connect: ' . mysql_error());
}
echo 'Connected successfully';
mysql_close($link);

?>