mysqldump - 右命令执行错误

Question

I have the following code.

<?php
    $command = '/usr/bin/mysqldump --user=marvin --password=mypassword --host=localhost opencart_status > /var/www/marvin/backup.sql';
    $result = passthru($command, $report);
    if(!$report){
        echo "Error!";
    }
    else{
        echo "OK";
    }
?>

I tried to run the $command on putty in linux and everything is OK. But when I ran it in my php scirpt, the output was "OK" (echo "OK"), but no backup.sql was in my folder.