The Forgotten Server requires at least gcc 5.0, which is available in Debian 9.
1. Install the required software
The following command will install Git, CMake, a compiler and the libraries used by The Forgotten Server.
Git will be used to download the source code, and CMake will be used to generate the build files.
# apt-get install git cmake build-essential libluajit-5.1-dev libmariadb-dev-compat libboost-date-time-dev libboost-filesystem-dev libboost-system-dev libboost-iostreams-dev libpugixml-dev libcrypto++-dev libfmt-dev
Replace libmariadb-dev-compat with libmysqlclient-dev on Debian 8 and below.
2. Download the source code
$ git clone --recursive https://github.com/otland/forgottenserver.git
3. Generate the build files
$ cd forgottenserver
$ mkdir build && cd build
$ cmake ..
4. Build
$ make