I am using Craft on Ubuntu 12.04 servers without problems, but when trying to run it on Ubuntu 14.04 (trusty) I always get the message
Mcrypt is required.
I installed it, however, via...
apt-get install apache2 php5 mysql-server php5 php5-cli php5-common php5-curl php5-gd php5-mcrypt php5-mysql
...and restarted the web server afterwards. Any hints? Maybe this is a bug with the way craft checks for mcrypt?