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Installation

This section describes on how to install Xdebug.

How you install Xdebug depends on your system. There are the following possibilities:

Installing on Linux #

Installing Xdebug with a package manager is often the fastest way. Depending on your distribution, run the following command:

Xdebug's latest version is 3.1.6.

For packages that have the PHP version in the package name, such as in php81-php-xdebug3, you can substitute the PHP version with the one that matches the PHP version that you are running.

Linux distributions might be providing an old and/or outdated version. If the package manager installs a version that is no longer supported (see Supported Versions), please install Xdebug with PECL, or from source instead.

Installing with PECL #

You can install Xdebug through PECL on Linux & macOS with Homebrew.

Prerequisites:

Run: 

pecl install xdebug

On Apple M1 hardware, programs can either be compiled for the native M1/ARM64 architecture, or for the emulated x86_64 architecure. Sometimes there is a mismatch with the default and PECL will fail, or Xdebug won't load with a message such as: 

PHP Warning:  Failed loading Zend extension 'xdebug.so' (tried: /opt/homebrew/lib/php/pecl/20190902/xdebug.so (dlopen(/opt/homebrew/lib/php/pecl/20190902/xdebug.so, 9): no suitable image found.  Did find:
        /opt/homebrew/lib/php/pecl/20190902/xdebug.so: mach-o, but wrong architecture
        /opt/homebrew/lib/php/pecl/20190902/xdebug.so: stat() failed with errno=22), /opt/homebrew/lib/php/pecl/20190902/xdebug.so.so (dlopen(/opt/homebrew/lib/php/pecl/20190902/xdebug.so.so, 9): image not found)) in Unknown on line 0

You can verify what your PHP's architecture is with: 

file `which php`

If that says arm64e, then you need to run: 

arch -arm64 sudo pecl install xdebug

And if it's x86_64, then you need to run: 

arch -x86_64 sudo pecl install xdebug

You should ignore any prompts to add "extension=xdebug.so" to php.ini — this will cause problems.

In some cases pecl will change the php.ini file to add a configuration line to load Xdebug. You can check whether it did by running php -v. If Xdebug shows up with a version number, than you're all set and you can configure Xdebug's other functions, such as Step Debugging, or Profiling.

If pecl did not add the right line, skip to the Configure PHP section.

1 On macOS, you should have PHP installed with Homebrew.

Installing on Windows #

There are a few precompiled modules for Windows, they are all for the non-debug version of PHP. You can get those at the download page. Follow these instructions to get Xdebug installed.

Installation From Source #

Obtain #

You can download the source of the latest stable release 3.1.6.

Alternatively you can obtain Xdebug from GIT: 

git clone git://github.com/xdebug/xdebug.git

This will checkout the latest development version which is currently 3.2.0dev. This development branch might not always work as expected, and may have bugs.

You can also browse the source on GitHub at https://github.com/xdebug/xdebug.

Compile #

There is a wizard available that provides you with the correct file to download, and which paths to use.

You compile Xdebug separately from the rest of PHP. You need access to the scripts phpize and php-config. If your system does not have phpize and php-config, you will need to install the PHP development headers.

Debian users can do that with: 

apt-get install php-dev

And RedHat and Fedora users with: 

yum install php-devel

It is important that the source version matches the installed version as there are slight, but important, differences between PHP versions. Once you have access to phpize and php-config, take the following steps:

  1. Unpack the tarball:

    tar -xzf xdebug-3.1.6.tgz

    You should not unpack the tarball inside the PHP source code tree. Xdebug is compiled separately, all by itself, as stated above.

  2. cd xdebug-3.1.6

  3. phpize

    If phpize is not in your path, please make sure that it is by expanding the PATH environment variable. Make sure you use the phpize that belongs to the PHP version that you want to use Xdebug with. See this FAQ entry if you're having some issues with finding which phpize to use.

  4. ./configure --enable-xdebug

  5. make

  6. make install

Configure PHP #

  1. Find out which PHP ini file to modify.

    Run a script with the following to find all configuration files that PHP has loaded:

    <?php
var_dump(php_ini_loaded_file(), php_ini_scanned_files());

    Alternatively, you can run php --ini on the command line.

    If there is a file with xdebug in the name, such as /etc/php/7.4/cli/conf.d/99-xdebug.ini, then this is the file to use.

    If that file does not exist, but there are other files in a conf.d or similar directory, you can create a new file there too. Please name it 99-xdebug.ini in that case.

    Otherwise, modify the php.ini file that is displayed through the script, or php --ini command.

    There could be more than one php.ini file. In many set-ups there is a different one for the command line (often cli/php.ini) and the web server (often fpm/php.ini).

    If you want to use Xdebug and OPCache together, you must have the zend_extension line for Xdebug below the line for OPCache, or in a file starting with a higher number (ie. 99-xdebug.ini vs 20-opcache.ini), otherwise they won't work properly together.

  2. Add the following line to this PHP ini file:

    zend_extension=xdebug

  3. Restart your webserver, or PHP-FPM, depending on what you are using.

  4. Verify that Xdebug is now loaded.

    Create a PHP page that calls xdebug_info(). If you request the page through the browser, it should show you an overview of Xdebug's settings and log messages.

    On the command line, you can also run php -v. Xdebug and its version number should be present as in:

    PHP 7.4.10 (cli) (built: Aug 18 2020 09:37:14) ( NTS DEBUG )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies
  with Zend OPcache v7.4.10-dev, Copyright (c), by Zend Technologies
  with Xdebug v3.0.0-dev, Copyright (c) 2002-2020, by Derick Rethans

    If Xdebug does not show up, or you get a warning from PHP that an xdebug.so file or similar was not found, you might need to use the full path instead of just zend_extension=xdebug, such as zend_extension=/usr/lib/php/20190902/xdebug.so.

    On Windows, you should place the php_xdebug.dll in the ext/ directory, which is a child directory in your PHP installation tree.

If you have trouble with this, please refer to the installation wizard to help you guide through this process.

With Xdebug loaded, you can now enable individual features, such as Step Debugging, or Profiling.

Related Content #

  • Activation and Triggers

    This video explains how to activate, through triggers and other method's Xdebug's step debugger, profiler, and tracer.

  • Xdebug 3: Diagnostics

    This video teaches you how to troubleshoot your Xdebug setup. It explains how to find out how Xdebug is configured, which settings have been made, and what it is attempting to do regarding its different features.

  • Xdebug 3: Modes

    This video introduces Xdebug 3's modes — the new way to configure which parts of Xdebug you have enabled.

Related Settings and Functions #

Settings #

string xdebug.log = #

Configures Xdebug's log file.

Xdebug will log to this file all file creations issues, Step Debugging connection attempts, failures, and debug communication.

Enable this functionality by setting the value to a absolute path. Make sure that the system user that PHP runs at (such as www-data if you are running with Apache) can create and write to the file.

The file is opened in append-mode, and will therefore not be overwritten by default. There is no concurrency protection available.

The log file will include any attempt that Xdebug makes to connect to an IDE:

[2693358] Log opened at 2020-09-02 07:19:09.616195
[2693358] [Step Debug] INFO: Connecting to configured address/port: localhost:9003.
[2693358] [Step Debug] ERR: Could not connect to debugging client. Tried: localhost:9003 (through xdebug.client_host/xdebug.client_port).
[2693358] [Profiler] ERR: File '/foo/cachegrind.out.2693358' could not be opened.
[2693358] [Profiler] WARN: /foo: No such file or directory
[2693358] [Tracing] ERR: File '/foo/trace.1485761369' could not be opened.
[2693358] [Tracing] WARN: /foo: No such file or directory
[2693358] Log closed at 2020-09-02 07:19:09.617510

It includes the opening time (2020-09-02 07:19:09.616195), the IP/Hostname and port Xdebug is trying to connect to (localhost:9003), and whether it succeeded (Connected to client). The number in brackets ([2693358]) is the Process ID.

It includes:

[2693358]
process ID in brackets
2020-09-02 07:19:09.616195
opening time

For Step Debugging:

INFO: Connecting to configured address/port: localhost:9003.
ERR: Could not connect to debugging client. Tried: localhost:9003 (through xdebug.client_host/xdebug.client_port).

For Profiling:

ERR: File '/foo/cachegrind.out.2693358' could not be opened.
WARN: /foo: No such file or directory

For Function Trace:

ERR: File '/foo/trace.1485761369' could not be opened.
WARN: /foo: No such file or directory

All warnings and errors are described on the Description of errors page, with detailed instructions on how to resolve the problem, if possible. All errors are always logged through PHP's internal logging mechanism (configured with error_log in php.ini). All warnings and errors also show up in the diagnostics log that you can view by calling xdebug_info().

Step Debugger Communication

The debugging log can also log the communication between Xdebug and an IDE. This communication is in XML, and starts with the <init XML element:

<init
    xmlns="urn:debugger_protocol_v1" xmlns:xdebug="https://xdebug.org/dbgp/xdebug"
    fileuri="file:///home/httpd/www.xdebug.org/html/router.php"
    language="PHP" xdebug:language_version="7.4.11-dev"
    protocol_version="1.0" appid="2693358" idekey="XDEBUG_ECLIPSE">
        <engine version="3.0.0-dev"><![CDATA[Xdebug]]></engine>
        <author><![CDATA[Derick Rethans]]></author>
        <url><![CDATA[https://xdebug.org]]></url>
        <copyright><![CDATA[Copyright (c) 2002-2020 by Derick Rethans]]></copyright>
</init>

The fileuri attribute lists the entry point of your application, which can be useful to compare to breakpoint_set commands to see if path mappings are set-up correctly.

Beyond the <init element, you will find the configuration of features:

<- feature_set -i 4 -n extended_properties -v 1
-> <response
       xmlns="urn:debugger_protocol_v1" xmlns:xdebug="https://xdebug.org/dbgp/xdebug"
       command="feature_set" transaction_id="4" feature="extended_properties" success="1">
   </response>

And continuation commands:

<- step_into -i 9
-> <response
       xmlns="urn:debugger_protocol_v1" xmlns:xdebug="https://xdebug.org/dbgp/xdebug"
       command="step_into" transaction_id="9"
       status="break" reason="ok">
           <xdebug:message filename="file:///home/httpd/www.xdebug.org/html/router.php" lineno="3">
           </xdebug:message>
   </response>

You can read about DBGP - A common debugger protocol specification at its dedicated documation page.

The xdebug.log_level setting controls how much information is logged.

Many Linux distributions now use systemd, which implements private tmp directories. This means that when PHP is run through a web server or as PHP-FPM, the /tmp directory is prefixed with something akin to: 

/tmp/systemd-private-ea3cfa882b4e478993e1994033fc5feb-apache.service-FfWZRg

This setting can additionally be configured through the XDEBUG_CONFIG environment variable.

integer xdebug.log_level = 7 #

Configures which logging messages should be added to the log file.

The log file is configured with the xdebug.log setting.

The following levels are supported:

LevelNameExample
0CriticalsErrors in the configuration
1ErrorsConnection errors
3WarningsConnection warnings
5CommunicationProtocol messages
7InformationInformation while connecting
10DebugBreakpoint resolving information

Criticals, errors, and warnings always show up in the diagnostics log that you can view by calling xdebug_info().

Criticals and errors are additionally logged through PHP's internal logging mechanism (configured with error_log in php.ini).

This setting can additionally be configured through the XDEBUG_CONFIG environment variable.

string xdebug.mode = develop #

This setting controls which Xdebug features are enabled.

This setting can only be set in php.ini or files like 99-xdebug.ini that are read when a PHP process starts (directly, or through php-fpm), but not in .htaccess and .user.ini files, which are read per-request.

The following values are accepted:

off
Nothing is enabled. Xdebug does no work besides checking whether functionality is enabled. Use this setting if you want close to 0 overhead.
develop
Enables Development Helpers including the overloaded var_dump().
coverage
Enables Code Coverage Analysis to generate code coverage reports, mainly in combination with PHPUnit.
debug
Enables Step Debugging. This can be used to step through your code while it is running, and analyse values of variables.
gcstats
Enables Garbage Collection Statistics to collect statistics about PHP's Garbage Collection Mechanism.
profile
Enables Profiling, with which you can analyse performance bottlenecks with tools like KCacheGrind.
trace
Enables the Function Trace feature, which allows you record every function call, including arguments, variable assignment, and return value that is made during a request to a file.

You can enable multiple modes at the same time by comma separating their identifiers as value to xdebug.mode: xdebug.mode=develop,trace.

XDEBUG_MODE environment variable

You can also set Xdebug's mode by setting the XDEBUG_MODE environment variable on the command-line; this will take precedence over the xdebug.mode setting, but will not change the value of the xdebug.mode setting.

Some web servers have a configuration option to prevent environment variables from being propagated to PHP and Xdebug.

For example, PHP-FPM has a clear_env configuration setting that is on by default, which you will need to turn off if you want to use XDEBUG_MODE.

Make sure that your web server does not clean the environment, or specifically allows the XDEBUG_MODE environment variable to be passed on.

Functions #

xdebug_info( string $category = null ) : mixed #

Show and retrieve diagnostic information

This function presents APIs to retrieve information about Xdebug itself. Which information gets returned, or displayed, depends on which arguments, or none at all, are given.

$category =

Without arguments, this function returns an HTML page which shows diagnostic information. It is analogous to PHP's phpinfo() function.

The HTML output includes which mode is active, what the settings are, and diagnostic information in case there are problems with debugging connections, opening of files, etc.

Each warning and error in the diagnostics log also links through to the Description of errors documentation page.

$category = 'mode' (New in Xdebug 3.1)

The function returns an array of all the enabled modes, whether through xdebug.mode or the XDEBUG_MODE environment variable.

Example:

<?php
var_dump( xdebug_info( 'mode' ) );
?>

Returns:

array(3) {
  [0] =>
  string(5) "debug"
  [1] =>
  string(7) "develop"
  [2] =>
  string(5) "trace"
}

$category = 'extension-flags' (New in Xdebug 3.1)

The function returns an array of all the compile flags that were enabled when running ./configure as part of Xdebug's compilation process.

The only flag that is available, is the compression flag. If this flag is enabled, then the xdebug.use_compression setting is available, and enabled by default.

Profiling and Function Trace will create GZip compressed files if the xdebug.use_compression setting is turned on (the default).

Example:

<?php
var_dump( xdebug_info( 'extension-flags' ) );
?>

Returns:

array(1) {
  [0] =>
  string(11) "compression"
}