Installation

Build click and install it via adb

./build.sh rel && ./install.sh

...or find it in the Ubuntu Store

https://uappexplorer.com/app/textsecure.jani

Make sure not to enter a leading zero when registering your number, i.e. there should not be a 0 after the country prefix (e.g. +49). Otherwise peers will have problems sending messages to you.