I just downloaded the latest version of wordpress onto AWS EC2 instance today and tried to install it but I cannot proceed as an error shown up on screen “Error establishing a database connection”. The error_log logged the following error:

Warning: mysqli_real_connect(): (HY000/2002): Permission denied in /var/www/wordpress/wp-includes/wp-db.php on line 1452

Deprecated: mysql_connect(): The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead in /var/www/wordpress/wp-includes/wp-db.php on line 1482

Warning: mysql_connect(): Permission denied in /var/www/wordpress/wp-includes/wp-db.php on line 1482

I have tried these two scripts directly on ec2 instance:

// test1.php - old db driver(will be removed in php 7, which will be released soon)
<?php
$servername = "sample.rds.amazonaws.com:3306";
$username = "mywordpress";
$password = "mywordpress";

$db = @mysql_connect($servername, $username, $password);
if (!$db) echo "connection failed";
else echo "connection succeeded";

mysql_close($db);
?>

and

// test2.php - recommended db driver by mysql and php7
<?php
$servername = "sample.rds.amazonaws.com:3306";
$username = "mywordpress";
$password = "mywordpress";

$mysqli = new mysqli($servername, $username, $password, 'mydb');

/*
 * This is the "official" OO way to do it,
 * BUT $connect_error was broken until PHP 5.2.9 and 5.3.0.
 */
if ($mysqli->connect_error) {
    die('Connect Error (' . $mysqli->connect_errno . ') '
            . $mysqli->connect_error);
}

/*
 * Use this instead of $connect_error if you need to ensure
 * compatibility with PHP versions prior to 5.2.9 and 5.3.0.
 */
if (mysqli_connect_error()) {
    die('Connect Error (' . mysqli_connect_errno() . ') '
            . mysqli_connect_error());
}

echo 'Success... ' . $mysqli->host_info . "\n";

$mysqli->close();
?>

both worked just fine. But once I go back to wordpress installation page(mysite.com/install.php), I always encountered same error.

any ideas, guys? Please help…

My server environment is:
OS: CentOS 7 x86_64
PHP: php 5.6 with php56_mysqlnd and php56w-fpm modules installed
nginx: 1.8
db: mysql 5.6 in AWS RDS