View source for Manual:How to debug

<languages/>
{{TOC|align|right}}
<translate>
<!--T:1-->
This page gives a basic introduction to '''debugging MediaWiki''' software.

<!--T:2-->
One of the first things you will notice is that "echo" generally does not work; this is part of the general design.
</translate>

<translate><!--T:8--> There are several configuration options to aid debugging. The following are all <tvar name=1><code>false</code></tvar> by default.</translate>
<translate><!--T:117--> Enable them by setting them to <tvar name=2><code>true</code></tvar> in your <tvar name=localsettings>{{ll|Manual:LocalSettings.php|LocalSettings.php}}</tvar>:</translate>

* {{wg|ShowExceptionDetails}} <translate><!--T:9--> Enable more details (like a stack trace) to be shown on the "Fatal error" page.</translate>
* {{wg|DebugToolbar}} <translate><!--T:10--> Shows a toolbar on the page with profiling, log messages and more.</translate>
* {{wg|ShowDebug}} <translate><!--T:11--> Adds the "log messages" part of wgDebugToolbar as a raw list to the page.</translate>
* {{wg|DevelopmentWarnings}} <translate><!--T:12--> MediaWiki will throw notices for some possible error conditions and for deprecated functions.</translate>

<translate>
<!--T:108-->
Example line to be added in your <tvar name=1>{{ll|Manual:LocalSettings.php|LocalSettings.php}}</tvar>:
</translate>

<syntaxhighlight lang="php">
$wgShowExceptionDetails = true;
</syntaxhighlight>

<translate>
== PHP errors == <!--T:3-->

<!--T:4-->
To see PHP errors, add this to the second line from the top (right below the <tvar name=1>{{phpi|<?php}}</tvar>) of <tvar name=2>{{ll|Manual:LocalSettings.php|LocalSettings.php}}</tvar>:
</translate>

<syntaxhighlight lang="php">
error_reporting( -1 );
ini_set( 'display_errors', 1 );
</syntaxhighlight>

<translate>
<!--T:5-->
Or set it in <tvar name=php-ini>{{ll|Manual:php.ini|php.ini}}</tvar>:
</translate>

<syntaxhighlight lang="ini">
error_reporting = E_ALL
display_errors = On
</syntaxhighlight>

<translate>
<!--T:43-->
Or set in .htaccess:
</translate>

<syntaxhighlight lang="apache">
php_value error_reporting -1
php_flag display_errors On
</syntaxhighlight>

<translate>
<!--T:6-->
This will cause PHP errors to be shown on-page. This might make it easier for attackers to find a way into your server, so disable it again when you have found the problem.
</translate>

<translate><!--T:7--> Note that ''fatal'' PHP errors may happen before the lines above are ever executed, or may prevent them from being shown.</translate>
<translate><!--T:118--> Fatal PHP errors are usually logged to Apache's error log – check the <code>[<tvar name=errorlog>https://php.net/error_log</tvar> error_log]</code> setting in <code>php.ini</code> (or use <code>[<tvar name=phpinfo>https://php.net/phpinfo</tvar> phpinfo()]</code>).</translate>

<translate>
=== Turning display_startup_errors on === <!--T:13-->
</translate>
<translate><!--T:14--> Some providers turn <tvar name=1><code>display_startup_errors</code></tvar> off, which hides the errors even if you raise the <tvar name=2><code>error_reporting</code></tvar> level.</translate>
<translate><!--T:119--> Turning it on within the program is too late! Instead you'll have to create a wrapper file around your file.</translate>
<translate><!--T:120--> In the case of MediaWiki you can just add this on top of <tvar name=1>mediawiki/index.php</tvar>:</translate>

<syntaxhighlight lang="php">
--- index.php
    error_reporting( -1 );
    ini_set( 'display_startup_errors', 1 );
    ini_set( 'display_errors', 1 );
</syntaxhighlight>

<translate>
<!--T:15-->
In other environments:
</translate>

<syntaxhighlight lang="php">
--- myTestFile.php
    error_reporting( -1 );
    ini_set( 'display_startup_errors', 1 );
    ini_set( 'display_errors', 1 );
    require 'your_file.php';
</syntaxhighlight>

<translate>
==SQL errors== <!--T:16-->

<!--T:17-->
To log all SQL queries, rather than just the one that raised the exception, set <tvar name=1>{{manual|$wgDebugDumpSql}}</tvar> in <tvar name=2><code>LocalSettings.php</code></tvar>:
</translate>

<syntaxhighlight lang="php">
$wgDebugDumpSql = true;
</syntaxhighlight>

{{MW version|version=1.16|version2=1.31}}
<translate>
<!--T:18-->
Prior to MediaWiki 1.32, you needed to set <tvar name=sqlerrors>{{manual|$wgShowSQLErrors}}</tvar> and <tvar name=backtrace>{{manual|$wgShowDBErrorBacktrace}}</tvar> to see details of database exceptions in the HTML output:
</translate>

<syntaxhighlight lang="php">
$wgShowSQLErrors = true;
$wgShowDBErrorBacktrace = true;
</syntaxhighlight>

<translate>
==In-depth debugging== <!--T:19-->

===Debugger=== <!--T:44-->

<!--T:113-->
You can debug your code step-by-step with <tvar name=1>{{ll|XDebug}}</tvar>. For some common setups, see:
</translate>

* [[MediaWiki-Docker/Configuration recipes/Xdebug|MediaWiki-Docker]]
* [[Cli/guide/Docker-Development-Environment/MediaWiki#XDebug|mwcli]]
* [[Manual:How to debug/with MediaWiki-Vagrant and PHPStorm|Vagrant with PHPStorm]]
* [[MediaWiki-Vagrant/Advanced_usage#MediaWiki_debugging_using_Xdebug_and_an_IDE_in_your_host|Vagrant with other IDEs]]
* [[Manual:Running_MediaWiki_on_macOS#Setting_up_XDebug_with_PhpStorm|MacOS]]

<translate><!--T:109--> MediaWiki-Vagrant has [<tvar name=url>https://phabricator.wikimedia.org/diffusion/MWVA/browse/master/puppet/modules/php/manifests/remote_debug.pp;c377718dea960c5e9e7b3acc79893a5e3c14da01$27</tvar> built in settings] for this.</translate>
<translate><!--T:110--> If you're not using MediaWiki-Vagrant, but your setup is similar, you can reuse those values.</translate>
<translate><!--T:111--> In some cases (e.g. due to a firewall), you may have to use the IDE on the same machine as the web server.</translate>
<translate><!--T:112--> In this case, simply set:</translate>

<syntaxhighlight lang="ini">
xdebug.remote_enable = 1
xdebug.remote_host = 'localhost'
</syntaxhighlight>

<translate>
<!--T:60-->
See the [<tvar name=xdebug>https://xdebug.org/docs/remote</tvar> XDebug documentation] for more information.

<!--T:78-->
To debug a command-line script (e.g. PHPUnit, or a maintenance script) on MediaWiki-Vagrant, use:
</translate>

<syntaxhighlight lang="php">
xdebug_on; php /vagrant/mediawiki/path/to/script.php --wiki=wiki ; xdebug_off
</syntaxhighlight>

<translate>
<!--T:79-->
Adjust the script, parameters, and remote host (it should be the IP of the computer where your IP is, 10.0.2.2 should work for <tvar name=1>[[MediaWiki-Vagrant]]</tvar>) as needed.

===Logging=== <!--T:20-->

<!--T:21-->
For much greater detail, you need to profile and log errors. 
</translate>

{{Note|1=<translate><!--T:93--> The instructions below are only valid for the default configuration.</translate> <translate><!--T:94--> If you change <tvar name=MWLoggerDefaultSpi><code>{{ll|Manual:$wgMWLoggerDefaultSpi|$wgMWLoggerDefaultSpi}}</code></tvar>, for example to enable the <tvar name=1><code>psr3</code></tvar> role on a <tvar name=vagrant>{{ll|MediaWiki-Vagrant|vagrant}}</tvar> box, these settings will probably be ignored.</translate> <translate><!--T:104--> In this case, see the documentation of your logger, for example, <tvar name=1>{{ll|Manual:MonologSpi}}</tvar>.</translate>}}

<translate>
==== Setting up a debug log file ==== <!--T:22-->

<!--T:23-->
To save errors and debugging information to a log, add <tvar name=logfile><code>{{ll|Manual:$wgDebugLogFile|$wgDebugLogFile}}</code></tvar> to the <tvar name=1><code>LocalSettings.php</code></tvar> file. Change the value to a text file where you want to save the debug trace output.
</translate>

<translate><!--T:24--> The MediaWiki software must have permissions from your operating system to create and write to this file, for example in a default Ubuntu install it runs as user & group <tvar name=1><code>www-data</code>:<code>www-data</code></tvar>.</translate>
<translate><!--T:102--> Here's a sample setting:</translate>

<syntaxhighlight lang="php">
/**
 * The debug log file must never be publicly accessible because it contains private data.
 * But ensure that the directory is writeable by the PHP script running within your Web server.
 * The filename is with the database name of the wiki.
 */
$wgDebugLogFile = "/var/log/mediawiki/debug-{$wgDBname}.log";
</syntaxhighlight>

<translate><!--T:25--> This file will contain much debug information from MediaWiki core and extensions.</translate>
<translate><!--T:103--> Some subsystems write to custom logs, see [[<tvar name=1>#Creating a custom log file</tvar>|#Creating a custom log file]] to capture their output.</translate>


{{warning|1=<translate><!--T:27--> The debug log file can contain private information such as login credentials, session cookies, and values of submitted forms. If this information is publicly accessible, attackers can use it to hack and compromise your machine and user account. If you need to share a debug log for diagnostic purposes, access the wiki without being logged in, and remove from the debug log any COOKIE lines, and don't capture any login attempt.</translate>}}

<translate>
==== Creating a custom log file ==== <!--T:28-->
</translate>
{{MW 1.31|and before}}
<translate><!--T:29--> Prior to MediaWiki 1.32, to create a custom log file that only holds your specific debug statements, use the <tvar name=1><code>wfErrorLog()</code></tvar> function.</translate>
<translate><!--T:100--> This function takes two arguments, the text string to log and the path to the log file:</translate>

<syntaxhighlight lang="php">
wfErrorLog( "An error occurred.\n", '/var/log/mediawiki/my-custom-debug.log' );
</syntaxhighlight>

<translate>
==== Creating custom log groups ==== <!--T:30-->
</translate>
<translate><!--T:31--> If you're debugging several different components, it may be useful to direct certain log groups to write to a separate file.</translate>
<translate><!--T:95--> See <tvar name=1>{{ll|Manual:$wgDebugLogGroups|$wgDebugLogGroups}}</tvar> for more information.</translate>

<translate>
<!--T:32-->
To set up custom log groups, use the following to LocalSettings.php:
</translate>

<syntaxhighlight lang="php">
/**
 * The debug log file should not be publicly accessible if it is used, as it
 * may contain private data. However, it must be in a directory to which PHP run
 * within your web server can write.
 *
 * Contrary to wgDebugLogFile, it is not necessary to include a wiki-id in these log file names
 * if you have multiple wikis. These log entries are prefixed with sufficient information to
 * identify the relevant wiki (web server hostname and wiki-id).
 */

// Groups from MediaWiki core
$wgDBerrorLog = '/var/log/mediawiki/dberror.log';
$wgDebugLogGroups = array(
	'exception' => '/var/log/mediawiki/exception.log',
	'resourceloader' => '/var/log/mediawiki/resourceloader.log',
	'ratelimit' => '/var/log/mediawiki/ratelimit.log',

	// Extra log groups from your extension
	#'myextension' => '/var/log/mediawiki/myextension.log',
	#'somegroup' => '/var/log/mediawiki/somegroup.log',
);
</syntaxhighlight>

<translate>
<!--T:33-->
To log to one of these groups, call <tvar name=1><code>wfDebugLog</code></tvar> like this:
</translate>

<syntaxhighlight lang="php">
if ( $module->hasFailed ) {
    wfDebugLog( 'myextension', "Something is not right, module {$module->name} failed." );
}
</syntaxhighlight>

{{Tip|1=<translate><!--T:34--> If you have carefully followed the instructions above but nothing gets written to your logging file(s), and if your system is using SELinux, have a look at the [[<tvar name=selinux>Special:MyLanguage/SELinux#Debug_logging_file</tvar>|logging section on the SELinux page]] to get around this SELinux context issue.</translate>}}

{{Tip|1=<translate><!--T:61--> Writing log files to the <tvar name=tmp><code>/tmp</code></tvar> directory may not generate any log file at all, even if the /tmp directory is supposed to be writable by anyone.</translate> <translate><!--T:62--> This could happen if your system is using one of the systemd features that create a virtual /tmp directory for that process.</translate> <translate><!--T:63--> If that's the case, configure your log file to be written into a different directory, like <tvar name=dir><code>/var/log/mediawiki</code></tvar></translate>}}

<translate>
==== Structured logging ==== <!--T:73-->
</translate>
{{MW 1.25|and after}}
<translate><!--T:74--> Structured logging allows you to include fields in your log records.</translate>
<translate><!--T:75--> See <tvar name=1>{{ll|Structured logging}}</tvar> for more information.</translate>

{{Note|1=<translate><!--T:77--> You will need to configure a better logger to collect the extra fields, for example Monolog.</translate>}}

<translate>
==== JavaScript error logging ==== <!--T:107-->
</translate>
{{MW 1.36|and after}}
<translate><!--T:114--> See the documentation of the <tvar name=1>{{ll|ResourceLoader/Core modules#mediawiki.errorLogger|mediawiki.errorLogger}}</tvar> <tvar name=2>ResourceLoader</tvar> module.</translate>

<translate>
=== Statistics === <!--T:66-->

<!--T:67-->
Advanced client-side logging can be performed with <tvar name=1>{{ll|Extension:EventLogging}}</tvar>, which requires a complex setup and careful inspection of privacy issues.

<!--T:68-->
Simple counting of certain kind of events is possible (since MediaWiki 1.25) using [<tvar name=url>https://github.com/etsy/statsd</tvar> StatsD]. StatsD offers meters, gauges, counters, and timing metrics.

<!--T:69-->
Usage example:
</translate>

<syntaxhighlight lang="php">
$stats = $context->getStats();
$stats->increment( 'resourceloader.cache.hits' );
$stats->timing( 'resourceloader.cache.rtt', $rtt );
</syntaxhighlight>

<translate><!--T:71--> The metrics can be sent to a StatsD server, which may be specified via the <tvar name=1><code>wgStatsdServer</code></tvar> configuration variable.</translate>
<translate><!--T:115--> (If not set, the metrics are discarded.)</translate>
<translate><!--T:116--> You can work with StatsD locally (without needing a Graphite server) by starting a <tvar name=statsd>[https://github.com/etsy/statsd StatsD]</tvar> server and configuring it with the "backends/console" backend, which will output metrics to the console.</translate>

<translate>
<!--T:72-->
As of MediaWiki 1.25, <tvar name=incrStats><code>wfIncrStats()</code></tvar> is a shortcut for the <tvar name=inc><code>increment()</code></tvar> method on the main <tvar name=1><code>RequestContext::getStats()</code></tvar> instance.

=== Send debug data to an HTML comment in the output === <!--T:35-->

<!--T:36-->
This may occasionally be useful when supporting a non-technical end-user. It's more secure than exposing the debug log file to the web, since the output only contains private data for the current user. But it's not ideal for development use since data is lost on fatal errors and redirects. Use on production sites is not recommended. Debug comments reveal information in page views which could potentially expose security risks.
</translate>

<syntaxhighlight lang="php">
$wgDebugComments = true;
</syntaxhighlight>

* {{ll|Manual:$wgDebugComments|$wgDebugComments}}

<translate>
===Working live with MediaWiki objects=== <!--T:38-->

<!--T:39-->
<tvar name=eval>{{ll|Manual:Eval.php|eval.php}}</tvar> is an interactive script to evaluate and interact with MediaWiki objects and functions in a fully initialized environment.
</translate>

<pre>
 $ php maintenance/eval.php
 > print wfMessage("Recentchanges")->plain();
 Recent changes
</pre>

<translate>
<!--T:40-->
The <tvar name=1>{{ll|MediaWiki-Vagrant}}</tvar> portable virtual machine integrates the interactive PHP shell <tvar name=2><code>phpsh</code></tvar> (when using Zend).

===Callable updates=== <!--T:81-->
</translate>
<translate><!--T:82--> Code embedded in the <tvar name=1><code>DeferredUpdates::addCallableUpdate()</code></tvar> function, such as <tvar name=2><code>$rc->save()</code></tvar> in <tvar name=3><code>RecentChange.php</code></tvar>, is not executed during the web request, so no error message will be displayed if it fails.</translate>
<translate><!--T:83--> For debugging, it may be helpful to temporarily remove the code from within the function so that it is executed live.</translate>

<translate>
===Interactive shell=== <!--T:105-->

<!--T:106-->
You can use <tvar name=shell>{{ll|Manual:shell.php|shell.php}}</tvar> as a PHP [[w:REPL|REPL]] with full access to MediaWiki internals.</translate>

<translate>
==Client side debugging (JavaScript)== <!--T:84-->
</translate>
<translate><!--T:85--> Wikipedia offers a rich set of tools for debugging client side JavaScript.</translate>
<translate><!--T:86--> In addition to the MediaWiki tools, other techniques are available to assist with diagnosing client interactions.</translate>

<translate>
<!--T:87-->
Tools:

<!--T:88-->
* <tvar name=2>{{ll|ResourceLoader}}</tvar> offers [[<tvar name=1>Special:MyLanguage/ResourceLoader/Developing with ResourceLoader#Debugging</tvar>|a means to ensure JavaScript]] is easily viewable by client-side tools.</translate>
<translate>
<!--T:97-->
* Open your browser's console.</translate> <translate><!--T:89--> Many client side mediawiki scripts log error messages to the console using ResourceLoader, which provides [[<tvar name=1>Special:MyLanguage/ResourceLoader/Modules#mediaWiki.log</tvar>|a safety oriented way]] to log to the client console. Beyond the native JavaScript logging function, it provides a check to ensure that a console is available and that logging does not produce its own error.</translate> <translate><!--T:90--> [[<tvar name=1>Special:MyLanguage/ResourceLoader/Architecture#Debug_mode</tvar>|ResourceLoader/Architecture#Debug_mode]] also describes this feature.</translate>
<translate>
<!--T:91-->
* Browser tools may provide native functionality to debug client side script.</translate>
<translate>
<!--T:92-->
* Network tracers, like [<tvar name=url>https://www.wireshark.org/</tvar> Wireshark] can provide insight into the script that is being provided by a page.</translate>
<translate>
<!--T:101-->
* You can add <tvar name=1><code>?debug=true</code></tvar> to your URL as in <tvar name=url>https://www.mediawiki.org/wiki/MediaWiki?debug=true</tvar> to get more detailed information for debugging via your browser's console

==See also== <!--T:41-->
</translate>
* {{ll|Manual:How to debug/Login problems}}
* {{ll|Manual:Profiling|Manual:Profiling}}
<translate>
<!--T:42-->
* ResourceLoader: [[<tvar name=1>Special:MyLanguage/ResourceLoader/Developing with ResourceLoader#Debugging</tvar>|ResourceLoader/Developing with ResourceLoader#Debugging]]</translate>
<translate>
<!--T:98-->
* All configuration variables related to debugging/logging: [[<tvar name=debug-log>Special:MyLanguage/Manual:Configuration settings#Debug/logging</tvar>|Manual:Configuration settings#Debug/logging]]</translate>
<translate>
<!--T:99-->
* Useful debugging tip: <tvar name=1><code>throw new MWException( 'foo' );</code></tvar> (dies with the given message and prints the callstack)
</translate>
* {{ll|Manual:Errors and symptoms}}
* {{ll|Category:Debug variables}}
* [[:wikitech:Debugging in production]] - <translate><!--T:76--> Debugging on Wikimedia's production cluster</translate>
* {{ll|Help:Locating broken scripts}}

[[Category:MediaWiki development{{#translation:}}]]
[[Category:Log{{#translation:}}]]
[[Category:Debug{{#translation:}}]]