You need to compile PHP with the --with-mcrypt[=DIR] parameter to enable this extension. DIR is the mcrypt install directory. Make sure you compile libmcrypt with the option --disable-posix-threads .
If using a Debian-based Linux system, you can run the following commands:
sudo apt-get install php5-mcrypt
sudo /etc/init.d/apache2 restart
You can install Mcrypt from the PHP Source Tree as a module if you choose.
You first need to ensure you have libmcrypt, libmcrypt-devel, and mcrypt installed, then do:
# cd php-5.x.x/ext/mcrypt
# phpize
# aclocal
# ./configure
# make && make install
Enable the module by adding: 'extension=mcrypt.so' to PHP.ini.
Done!
Very handy if you need to install a single module and you may have installed PHP via RPM, but don't wish to recompile your whole PHP install.
Mcrypt.dll should be included in the WINDOWS installer of PHP.
Or in the WINDOWS installer of phpmyadmin.
For recent versions of mcrypt, you must also use the compile option "--enable-dynamic-loading", so you need both of these:
--disable-posix-threads --enable-dynamic-loading
In case you are an operator and you are not familiar with the generation of software you must know, that the installation of additional libraries may be insufficient. You may suffer a malfuntion of the package with the known http server log message: "Cannot load mcrypt extension. Please check your PHP configuration." although you expect the configuration to be right.
For an operator, generation of software is inconvenient. Instead you should check your PHP basic installation. The problem may be that you do not have extracted the mcrypt extension during the installation process. Using the Windows installer, you may change your installation by rerunning the setup. In case you have the right php.ini, the extension declaration in php.ini and libmcrypt.dll in the system path the extension should work. Keep control in the http server log!
If you wish to install mcrypt on Windows, you should also place libmcrypt.dll in the PATH of your system.