Ubuntu: PHP mCrypt Installation
mCrypt is an encryption program used on Linux systems.
To install mCrypt for PHP5 on your Ubuntu Linux system:
sudo apt-get install php5-mcrypt
Then restart Apache with:
sudo /etc/init.d/apache2 restart
I needed to do this so that phpMyAdmin would have mcrypt available.
For more info about mcrypt, visit:
Official site
http://mcrypt.hellug.gr
PHP usage of mCrypt
http://www.php.net/manual/en/book.mcrypt.php