XDEBUG EXTENSION FOR PHP | DOCUMENTATION
Frequently Asked Questions
- Q: phpinfo() reports that Xdebug is installed and enabled, yet I
still don't get any stacktraces when an error happens.
- A1: You have to search through all your PHP libraries and include files for any
"set_error_handler" calls. If there are any, you have to either comment it out,
or change the body of the handler function to call xdebug_* api functions.
- A2: You do not have set display_errors to 1 in php.ini
- Q: Xdebug doesn't format output.
- A: Make sure you have PHP's html_errors set to 1 in php.ini
- Q: The debug client doesn't receive any connections, what do I do
- A: You probably forgot to set the environment variable or to add
the necessary information to your URL. See the
- A: Have you checked your firewall settings? Make sure the port Xdebug is
listening on (default 9000) is not blocked.
- A: Are you using FastCGI? It uses the same port by default as Xdebug (9000)
so you will need to change one of them to a different number. In Xdebug you can
do that with xdebug.xdebug.remote_port.
- A: If you are running with SELinux you should make sure it is not
preventing connections; look for warnings about
anything related to the Xdebug port. You might have to allow access explicitly.
Visit this site or
search for "selinux name_connect apache" for more information about how to do
Compilation and Configuration
Q: I don't have the
- A: Debian and Ubuntu users need to install the
Q: What to do with: Xdebug requires Zend Engine API version
xxxxxxxx. The Zend Engine API version 2xxxxxxxx which is
installed, is newer.
This message means that you are trying to load Xdebug with a PHP version for
which it wasn't built. If you compiled PHP yourself, it is most likely because
you compiled Xdebug against PHP headers that belong to a different PHP version
that you're running. For example, you're using PHP 5.3 and the headers
you're using are still PHP 5.2. If you are using a pre-compiled binary, then
you're using the wrong one.
- To diagnose if this is your problem, make the following steps:
- Check what the "Zend Extension" API number is of the PHP version that you
are running by looking at phpinfo() (or "php -i") output. You can find it in
the top part of the output, in the same block as the PHP logo and the PHP
version. As examples, for PHP 5.2, the number is "220060519" and for PHP 5.3 it
- Check what the output of "phpize" is when you're completing the
compilation steps. The number that you're looking for is on the line that says
"Zend Extension Api No".
If the two numbers from above do not match, you're compiling with the
wrong PHP headers. Refer to the next FAQ
entry to figure out which phpize to use.
- Q: Xdebug is only loaded as PHP extension and not as a Zend Extension.
The tailored installation intstructions might have you pointed to this entry.
In order for Xdebug to work properly, including breakpoints etc. it is required that it is loaded
as a Zend extension, and not just as a normal PHP extension. Some installation
tools (PEAR/PECL) sometimes advice you to use
to load Xdebug. This is not correct. In order to fix this issue, please
look for a line
extension=xdebug.so in any of the INI files that
are listed under "Loaded Configuration File" and "Additional .ini files parsed"
in the top block. Remove this line, and go back to the
Tailored Installation Instructions.
- Q: How do I find which phpize to use?
Run: "phpize --help". This shows you the full path to
phpize. This path should be the same as where you have the CLI binary,
"php-config" and the "pear" and "pecl" binaries installed. If you
run "php-config --version" it should show the same version of PHP that
you're running. If it doesn't match up, and perhaps the wrong "phpize"
binary is found on the path, you can run configure as follows:
- ./configure --with-php-config=/full/path/to/php/bin/php-config
- Q: I'm using XAMPP, but I can't seem to get the packaged xdebug extension
to work properly.
- A: If you uncommented the "extension=php_xdebug.dll" line, that is to be
expected. Xdebug needs to be loaded with the zend_extension_ts=
"C:\path\to\php_xdebug.dll" directive. You'll also likely have to disable the
loading of the Zend Optimizer, since it's enabled by default, and doesn't work
well with Xdebug. So look for the related entry in php.ini, and comment it out.
From PHP 5.3 onwards, you always need to use the zend_extension PHP.ini
setting name, and not zend_extension_ts.
- Q: On Debian, I am seeing the following problem with the build of
Xdebug.... any fixes?
In function `__i686.get_pc_thunk.bx':
: multiple definition of `__i686.get_pc_thunk.bx'
(.gnu.linkonce.t.__i686.get_pc_thunk.bx+0x0): first defined here
collect2: ld returned 1 exit status
make: *** [xdebug.la] Error 1
- A: This is an issue with Debian itself, see for more information