Install Solr 7 for Drupal 8 Search API on Ubuntu 16.04
A brief introduction to Search API Solr, an update on the ecosystem and how to get Search API 2.x working on a dev environment with multiple collections.
If you terminal looks like this after running apt-get update :
W: GPG error: http://ppa.launchpad.net/ondrej/php/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY {whatever}
W: The repository 'http://ppa.launchpad.net/ondrej/php/ubuntu xenial InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.