Add a new documentation page about Freeciv21 on servers

docs/General/index.rst

@@ -10,6 +10,7 @@ the FAQ and installation instructions go here.
   install.rst
   windows-install.rst
   modpack-installer.rst
+  on-the-server.rst
   :maxdepth: 1
 
 Manuals

docs/General/on-the-server.rst

@@ -0,0 +1,109 @@
+..
+    SPDX-License-Identifier: GPL-3.0-or-later
+    SPDX-FileCopyrightText: 2022 louis94 <[email protected]>
+
+Freeciv21 on the Server
+***********************
+
+In order to play Freeciv21 on the network, one machine needs to act as the *server*: the state of
+the game lives on the server and players can connect to play. There are many ways to operate such a
+server; this page gives an introduction to the topic.
+
+In order to run a server, you need a computer that other players can reach over the network. If
+you're planning to play at home, this can usually be any machine connected to your WiFi or local
+cabled network. Otherwise, the easiest is to rent a small server from a hosting provider. We
+strongly recommend that you choose a Linux-based server, as that is what we have experience with.
+You will need the ability to run your own programs on the server, so SSH access is a must. Apart
+from that, Freeciv21 is quite light on resources so you will hardly hit the limits of even the
+cheapest options.
+
+Whether you choose to use your own machine or to rent one, the basic principle of operating a
+server is the same: you need to run a program called ``freeciv21-server`` for as long as the game
+will last. This program will wait for players to connect and handle their moves in the exact same
+way as in a single player game. In fact, Freeciv21 always uses a server, even when there is only
+one player!
+
+Installation
+============
+
+Installing Freeciv21 on a server is done the normal way, as documented in :doc:`/General/install`.
+Because the official packages come with the complete game, they will pull a number of dependencies
+that are normally not used on servers (for instance, a display server). This software is installed
+for packaging reasons, but will not be used.
+
+Starting the Server
+===================
+
+Once Freeciv21 is installed, it's immediately ready to run a simple server, which one can do by
+running the following command:
+
+.. code-block:: sh
+
+    freeciv21-server
+
+This starts a server listening on the port traditionally used for Freeciv21, 5556. You can provide
+a custom port number by passing it to the ``-p`` argument:
+
+.. code-block:: sh
+
+    freeciv21-server -p 5000
+
+A server started with this command can be reached by pointing the game to port 5000 of your domain
+name. We suggest to start the server from within a terminal multiplexer such as ``tmux`` or
+``screen``, which will let it run independently.
+
+User Permissions
+================
+
+Freeciv21 supports several access levels for players connected to a server, restricting which
+commands they are allowed to run:
+
+``none``
+    The user may not issue any command.
+
+``info``
+    The user may use informational commands only.
+
+``basic``
+    The user may use informational commands as well as commands affecting the game. Commands
+    affecting the game start a vote if more than one user is connected.
+
+``ctrl``
+    Same as ``basic``, but the vote is bypassed for commands affecting the game.
+
+``admin``
+    May use any command, except for ``quit``, ``rfcstyle``, and ``write``. This includes
+    potentially destructive commands such as ``save`` and ``fcdb`` --- use with care.
+
+``hack``
+    May use all commands without restriction.
+
+By default, users connected to your server have access level ``basic``. This can be changed using
+the ``cmdlevel`` command::
+
+    cmdlevel info new
+
+This command would grant access level ``info`` to any newly connecting player. A few more options
+are available; please refer to the documentation of ``cmdlevel`` for more information.
+
+.. note::
+    The ``take`` and ``observe`` commands require access level ``info`` only. Their use can be
+    restricted using the ``allowtake`` server option or, in more advanced setups, using the
+    ``user_take`` :doc:`fcdb </Coding/fcdb>` hook.
+
+Authentication
+==============
+
+By default, Freeciv21 servers are open to anyone without any sort of authentication. It is
+possible to make Freeciv21 ask for a password. There is also a built-in registration procedure
+with which one can create an account and set a password.
+
+Authentication needs vary greatly depending on what you do with your server. If you use passwords
+merely to prevent players from peeking on each other, you may be fine with a very basic setup. If
+you are planning to run a full-scale server allowing registration through a website, you will
+need much more advanced settings. Freeciv21 ought to support all use cases within a unified
+interface. To allow for the necessary flexibility, authentication support is implemented using a
+Lua script.
+
+See the :doc:`fcdb documentation </Coding/fcdb>` for more information about setting up
+authentication.