Question: I am using captcha and I want to create a captcha using the cpatcha helper!I read the user guide and write a piece of code,but it fails to create an captcha,also here is no error displayed on the page,so I just can't find where I am wrong,my code is as follows:

```
public function captcha(){
        $this->load->helper('captcha');

        $vals=array(
            'word'=>'0123456789',
            'img_path'=>base_url('asserts/cpatcha').'/',
            'img_url'=>base_url('asserts/cpatcha').'/',
            'img_width'=>150,
            'img_height'=>30,
            'expiration'=>7200
            );

        var_dump($vals);
        $cap=create_captcha($vals);
        var_dump($cap['image']);
    }

```

as I print the two variables,the result displayed on the page is as follows:

```
array (size=6)
  'word' => string '0123456789' (length=10)
  'img_path' => string 'http://wrecruit.tudouya.com/asserts/cpatcha/' (length=44)
  'img_url' => string 'http://wrecruit.tudouya.com/asserts/cpatcha/' (length=44)
  'img_width' => int 150
  'img_height' => int 30
  'expiration' => int 7200

null

```

Answer: 
I've encountered similar error when I forgot about another instance of `spark-shell` running on same node.
In my case I needed to create a directory and grant proper permissions:

```
$ sudo mkdir /var/lib/hive/metastore/
$ sudo chown hdfs:hdfs /var/lib/hive/metastore/

```