Install Mcrypt in linux

Command to install Mcrypt is as usual

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.
Now restart Apache and you can see Mcrypt working :)