title: Azure Linux VMSS add extension
body: <p>I have created a VMSS (VM scaleset) with the Azure portal, and I want to add a custom script extension to it to install some software on it. How do I do this? I have tried using <code>azure vmss config extensions set</code> with a json file, but that doesn't seem to work. My json file looks like</p>
  
  <pre><code>{
  "extensionProfile":{
      "extensions": [
          {
              "name": "bigstream spark",
              "properties": {
                  "publisher": "Microsoft.Azure.Extensions",
                  "type": "CustomScript",
                  "typeHandlerVersion": "2.0",
                  "autoUpgradeMinorVersion": true,
                  "settings": {
                          "fileUris": [&lt;some files....&gt;
                          ],
                          "commandToExecute": "./installspark2.sh"
                  },
                  "protectedSettings": {
                      "storageAccountName": &lt;accountname&gt;,
                      "storageAccountKey": &lt;secret&gt;
                  }
              }
          }]
      }
  }
  </code></pre>