I tried to install PHP7 in the workspace and it couldn't install because of permissions. Could anyone have done this? Or C9 can upgrade it for us? Even for PHP v5.6.*. It's PHP v5.5.9 currently installed :unamused ...
Very simple, you can first add the apt-repository for PHP7, purge old versions and install PHP7 as usually...
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update
sudo apt-get purge -y php*
sudo apt-get install -y php7.1 php7.1-cli php7.1-fpm
You can also use PHPBrew: https://community.c9.io/t/how-to-upgrade-to-php7/1379