take backup of MySql databases via php

<?php
$db_user = "****";
$db_pass = "****";
$db_host = "*****";
echo "<html>\n<p>@ ". date('Y-m-d H:i:s') . " Database backup started.";

$sql="SHOW DATABASES";
$link = mysqli_connect($db_host,$db_user,$db_pass) or die ('Error connecting to mysql: ' . mysqli_error($link).'\r\n');

if (!($result=mysqli_query($link,$sql))){
        printf("Error: %s\n", mysqli_error($link));
}

while( $row = mysqli_fetch_row( $result ) )
{
    if (($row[0]!="information_schema") && ($row[0]!="mysql"))
    {
        echo "\n\n<br>\n@ " . date('Y-m-d H:i:s') . " Exporting ".$row[0]." \n";
        $output = "mysqldump --opt -u ".$db_user." -h ".$db_host." -p".$db_pass." ".$row[0]." | bzip2 > /home/reenain/md/cron/01_db_backup/".$row[0].".sql.bz2";
        system($output);
    }
}

echo "\n\n<br>@ ". date('Y-m-d H:i:s') . " Database backup completed.\n\n</html>";
?>