When your code isn't doing what you want it to do, it's time to debug. There are lots of options for debugging and there is lots you can do without setting up a sophisticated debugging environment. This chapter contains some simple debugging tips and tricks to get you started and also instructions on setting up XDebug, which is the recommended debugging tool for CiviCRM when you have bugs which are really hard to squish.

Security Alert

None of these debugging should be performed on production sites, as they can expose system configuration and authentication information being to unauthorized visitors.

The debugging methods presented here are ordered with the easiest ones first, but you may find the more challenging methods near the end to be more rewarding.

Changing settings in the UI

CiviCRM has a debug mode which can be enabled via the UI to give you quick access to a couple of useful diagnostic tools, including all the Smarty variables that make up a page. It also provides shortcut methods to empty the file-based cache and session variables.

To use debugging via the UI, first go to Administer > System Settings > Debugging and Error Handling to enable these options, and find out more about them.

Using URL parameters

After enabling debugging, append any of the following name-value pairs to the URL for the page you visit.

  • &smartyDebug=1 opens the Smarty Debug Window which loads all variables available to the current page template into a pop-up window (make sure you have pop-up blocking disabled).
  • &sessionReset=2 resets all values in your client session.
  • &directoryCleanup=1 empties template cache in civicrm/templates_c.
  • &directoryCleanup=2 removes temporary upload files in civicrm/upload.
  • &directoryCleanup=3 performs both of the above actions.
  • &backtrace=1 displays a stack trace listing at the top of a page.
  • &sessionDebug=1 displays the current users session variables in the browser.
  • &angularDebug=1 displays live variable updates on certain Angular-based pages


  • Sometimes using &smartyDebug=1 to inspect variables available to a template will not work as expected. An example of this is looking at the Contact Summary page, when using this method will display the variables available only to the summary tab and you might want to see the variables available to one of the other tabs. To do this you will need to debug via code, as explained below.
  • If the page you are debugging does not already have a key-value parameter before debugging, you will need to begin the first parameter with a question mark instead of a ampersand.

Displaying a backtrace

The backtrace can be enabled independently of debugging. If this option is selected, a backtrace will be displayed even if debugging is disabled.

A backtrace is a list of all the functions that were run in the execution of the page, and the PHP files that contain these functions. It can be really useful in understanding the path that was taken through code, what gets executed where, etc.

Viewing log files

CiviCRM's log files are stored in the ConfigAndLog directory within CiviCRM's local file storage (see the File System documentation for details on your CMS). Most runtime errors are logged here, as well as data that you explicitly write to log using the CRM_Core_Error::debug log=true parameter.

Changing file-based settings

The following values can be added to your site's settings file civicrm.settings.php to assist in debugging:

  • define('CIVICRM_MAIL_LOG', 1); causes all outbound CiviCRM email to be written to a log file. No real emails are sent.

  • define('CIVICRM_MAIL_LOG', '/dev/null'); causes all outbound emails to be discarded. No email is sent and emails are not written to disk.

  • define('CIVICRM_DEBUG_LOG_QUERY', 1); outputs all SQL queries to a log file.

  • define('CIVICRM_DEBUG_LOG_QUERY', 'backtrace'); will include a backtrace of the PHP functions that led to the query.

  • define('CIVICRM_DAO_DEBUG', 1); writes out various data layer queries to your browser screen.

  • define('CIVICRM_CONTAINER_CACHE', 'never'); causes Civi to rebuild the container from the latest data on every page-load


When any sort of "logging stuff to a file" is enabled by one of the above settings, check the ConfigAndLog directory within the local files directory to find the log. (See the File System documentation for the location in your CMS.)

Viewing a query log from MySQL

Outside of CiviCRM, the MySQL general query log allows MySQL to log all queries. This is a performance killer, so avoid using it in production!

The relevant settings are:

# Location of the query log
# Enable/disable the query log

You can enable the query log at runtime via SQL, provided the path to the logfile is configured.

SET GLOBAL general_log = 'ON';
SET GLOBAL general_log = 'OFF';

And you can inspect the query log settings also:

mysql> show variables like '%general%';
| Variable_name    | Value                           |
| general_log      | OFF                             |
| general_log_file | /usr/local/var/mysql/strike.log |

Changing source code

In Smarty template files

Add {debug} to any part of the .tpl file and the Smarty Debug Window (described above) will display all variables in the same scope as the {debug} statement.

Printing PHP variables

Show the contents of a variable:


Show the contents of a variable, also with information regarding data types and lengths:


Another way to show the contents of a variable:

CRM_Core_Error::debug($name, $variable = null, $log = true, $html= true);

Stop the script execution at that point.


Print a backtrace:


In AngularJS HTML templates

<div crm-ui-debug="myData"></div>

Then, be sure to add the parameter angularDebug=1 to the URL.

Clearing the cache

Clearing the cache is not a debugging technique, specifically. But sometimes it helps, and so is mentioned here for the sake of completeness.

Using a web browser, either:

  • Navigate directly to civicrm/clearcache
  • Navigate to "Administer => System Settings => Cleanup Caches"

Using the command line, you can clear all caches with one of these commands:

  • cv flush (requires cv)
  • drush cc civicrm (requires drush)

Alternatively, you can call the following methods in PHP code:

  • civicrm_api3('System', 'flush', array()); clears many different caches
  • CRM_Core_Config::clearDBCache(); clears the database cache
  • CRM_Core_Config::cleanup(); clears the file cache

Running a debugger program

What is a debugger?

A debugger is a software program that watches your code while it executes and allows you to inspect, interrupt, and step through the code. That means you can stop the execution right before a critical juncture (for example, where something is crashing or producing bad data) and look at the values of all the variables and objects to make sure they are what you expect them to be. You can then step through the execution one line at a time and see exactly where and why things break down. It's no exaggeration to say that a debugger is a developer's best friend. It will save you countless hours of beating your head against your desk while you insert print statements everywhere to track down an elusive bug.

Debugging in PHP is a bit tricky because your code is actually running inside the PHP interpreter, which is itself (usually) running inside a web server. This web server may or may not be on the same machine where you're writing your code. If you're running your CiviCRM development instance on a separate server, you need a debugger that can communicate with you over the network. Luckily such a clever creature already exists: XDebug.

XDebug isn't the only PHP debugger, but it's the one we recommend for CiviCRM debugging.

Installing XDebug

Debian / Ubuntu Linux (System Packages)

sudo apt-get install php5-xdebug

Red Hat / CentOS Linux (System Packages)

sudo yum install php-pecl* php-devel php-pear
sudo pecl install Xdebug

Mac OS X, Windows, and others

Generic instructions are provided with XDebug's documentation.

Specific installation steps vary due to the diversity of PHP installation sources -- Apple's built-in PHP, brew, MAMP, XAMPP, AMPP, WAMP, Vagrant, Bitnami, and MacPorts are all a bit different. The best way to install XDebug is to identify your specific PHP runtime and then search Google, e.g. "mamp xdebug" or "macports xdebug".

Setting up PHP to talk to XDebug

Tell XDebug to start automatically (don't do this on a production server!) by adding the following two lines to your php.ini file (your php.ini file is a php configuration file which is found somewhere on your server. Calling the phpinfo() function is probably the easiest way to tell you where this file is in your case.

xdebug.remote_enable = On
xdebug.remote_autostart = 1

Once XDebug is installed and enabled in your PHP configuration, you'll need to restart your web server.

Installing an XDebug Front-End

After you have XDebug running on your PHP web server, you need to install a front-end to actually see what it is telling you about your code. There are a few different options available depending on what operating system you use.


NetBeans is a cross platform heavyweight Java IDE (Integrated Development Environment). It offers lots of features, but isn't exactly small or fast. However, it is very good at interactive debugging with XDebug. And since it's written in Java, it should run on any operating system you want to run it on.

After installing NetBeans, open your local CiviCRM installation in NetBeans and click the Debug button on the toolbar. It will fire up your web browser and start the debugger on CiviCRM. You may went to set a breakpoint in CRM/Core/Invoke.php to make the debugger pause there. For more information, see the NetBeans debugging documentation.


MacGDBp is a lighter-weight option, only available for OS X. After installing MacGDBp, launch it and make sure it says "Connecting" at the bottom in the status bar. If it doesn't, click the green "On" button in the upper-right corner to enable it. The next time you access CiviCRM, the web browser will appear to hang. If you click on MacGDBp, you'll see that it has stopped on the first line of code in CiviCRM. From there you can step through the code to the part you're interested in. But it's probably a better idea to set a breakpoint in the part of the code you're interested in stopping at. See the MacGDBp documentation for more information.