doc/ev3_linux: describe command line, set hostname

doc/api/start_ev3_linux.inc

@@ -1,10 +1,29 @@
-Accessing Advanced EV3 Features
+Accessing advanced EV3 features
 ===============================
 
+MicroPython runs on top of `ev3dev`_, which is a specific version of Linux.
+Linux is an *operating system*. (Other popular operating
+systems are Microsoft Windows and Apple macOS.) This means that your EV3 is
+almost like a real computer, just much smaller.
+
+.. note::
+
+   *If you just want to write MicroPython programs, you can skip the
+   remaining sections.*
+
+   The remaining sections are aimed at curious users who want go beyond
+   MicroPython and access some of the other built-in features of Linux and
+   ev3dev.
+
 The Linux command line
 -----------------------------------------
 
-Intro
+Although your EV3 Brick is quite like a real computer, you do not interact with
+it using a big screen and a mouse. Instead, you can access files and programs
+on it using the *command line*. It is also called the *terminal*.
+
+Follow the steps in :numref:`fig_terminal` to access the command line. Now
+you can enter commands by typing them in and pressing enter.
 
 .. _fig_terminal:
 
@@ -13,9 +32,79 @@ Intro
    :alt: files
    :align: center
 
-   Opening the Linux command line
+   Opening the Linux command line and running the ``ls`` command.
+
+**Running basic commands**
+
+For example, if you type the following command and press enter::
+
+   ls
+
+then you will see the contents of the current folder. :numref:`fig_terminal`
+shows the result: it listed the project folder of the ``getting_started``
+project that we just ran.
+
+If you type the following command and press enter::
+
+   exit
+
+then the command line will be closed. Alternatively, click the garbage icon
+shown in :numref:`fig_terminal`.
+
+You can copy text from the command line by selecting it and
+then pressing ``ctrl`` ``shift`` ``c``.
+You can paste text into the command line
+using ``ctrl`` ``shift`` ``v``.
+
+**Running commands as an administrator**
+
+Some commands require a password to run. This is similar to administrative
+tasks on your computer or tablet, such as installing a new app. These commands
+work like any other command, but you add ``sudo`` in front of
+them.
+
+As an exercise, you can run the following command to turn the EV3 Brick off::
+
+   sudo poweroff
+
+You will be prompted for a password. Type ``maker`` and then press ``Enter``.
+
+.. warning::
+
+   Only run commands with ``sudo`` if you know what you are doing.
+
+**Learning more about the command line**
+
+To learn more about the command line and many of the available commands, we
+recommend reading the beginner-friendly free ebook
+called `The Linux Command Line`_.
+
+To learn more about ev3dev-specific tips and tricks, visit the `ev3dev`_
+website.
 
 .. _hostname:
 
-Changing the EV3 Brick Name
+Changing the EV3 Brick name
 -----------------------------------------------------------
+
+When you search for your EV3 using Visual Studio Code, you see all EV3 Bricks
+listed by their name. By default, all EV3 Bricks are named *ev3dev*. Follow
+these steps to change that name:
+
+   1. Open Visual Studio Code and connect to your EV3 as usual.
+   2. Read the steps above about running commands as an administrator.
+   3. Think of a good name. In this example, we'll
+      call it ``autonomous-vehicle2``
+   4. Enter the following command and press enter::
+
+         sudo hostnamectl set-hostname autonomous-vehicle2
+
+   5. Reboot the EV3 Brick for the change to take effect.
+   6. You may need to reboot your computer as well.
+
+EV3 Brick names should only contain lowercase letters ``a`` through ``z``,
+the digits ``0`` through ``9``, and the hyphen ``-``. It must start with a
+letter or digit. It cannot include spaces or other symbols.
+
+.. _ev3dev: https://www.ev3dev.org/
+.. _The Linux Command Line: http://linuxcommand.org/tlcl.php