I am trying to install graph-tool on a Trusty Ubuntu virtualbox being hosted on a Mac. I've added the requisite lines deb http://downloads.skewed.de/apt/trusty trusty main deb-src http://downloads.skewed.de/apt/trusty trusty main to my /etc/apt/sources.list, but when I run a sudo apt-get update, I get the following errors: W: Failed to fetch http://downloads.skewed.de/apt/trusty/dists/trusty/Release Unable to find expected entry 'main/source/Sources' in Release file (Wrong sources.list entry or malformed file) E: Some index files failed to download. They have been ignored, or old ones used instead. I have the main, universe, and multiverse repositories available. If any one has come across this problem before, please let me know how to fix it. Thanks. Andy_