To turn on Joomla!'s Debug mode:

• Login to the Joomla administration e.g. http:/YOURSITE/administrator/
• At the top under the Site menu click Global Configuration.
• Click the System tab.
• Under the Debug Settings section change Debug System to Yes.
• Click the Save button.

Debug mode will output a list of all queries that were executed in order to generate the page. This will also turn on a stack trace output for error and warning pages. Hubzero components will also have PHP error reporting turned on, allowing one to see any PHP errors that may be present.

Note: Turning on debugging mode for production (live) sites is strongly discouraged and it is recommended to be avoided if at all possible.

Restricting who sees debug output

Since debug mode can contain potentially sensitive, it is strongly recommended that access to debug output is restricted to the administrator or super administrator user access levels and/or a defined list of users.

To restrict:

• Login to the Joomla administration e.g. http:/YOURSITE/administrator/
• At the top under the Extensions menu click Plugin Manager.
• Select System from the "Select Type" drop-down.
• Find the debug plugin, typically titled "System - Debug", and click to edit.
• Under the Parameters section select the Allowed Groups and/or enter a comma-seprated list of usernames into the Allows Users box.
• Click the Save button.

One encounters the following error:

Illegal variable _files or _env or _get or _post or _cookie or _server or _session or globals passed to script.

This error is generated when the key of a key-value pair is numeric in one of the following variables: _files or _env or _get or _post or _cookie or _server or _session or globals. An example of this would be $_POST[5] = 'value'. This is most often generated by having form elements with numeric values as names. For example:

<input type="text" name="5" />

As the error indicates, this is not allowed. Element names must include at least one non-numeric character. Examples:

<input type="text" name="n5" />

<input type="text" name="n_5" />