Linux is a family of free and open-source operating systems based on the Linux kernel. Operating systems based on Linux are known as Linux distributions or distros. Examples include Debian, Ubuntu, Fedora, CentOS, Gentoo, Arch Linux, and many others.
The Linux kernel has been under active development since 1991, and has proven to be extremely versatile and adaptable. You can find computers that run Linux in a wide variety of contexts all over the world, from web servers to cell phones. Today, 90% of all cloud infrastructure and 74% of the world’s smartphones are powered by Linux.
However, newcomers to Linux may find it somewhat difficult to approach, as Linux filesystems have a different structure than those found on Windows or MacOS. Additionally, Linux-based operating systems depend heavily on working with the command line interface, while most personal computers rely on graphical interfaces.
This guide serves as an introduction to important command line concepts and skills and equips newcomers to learn more about Linux.
Prerequisites
To follow along with this guide, you will need access to a computer running a Linux-based operating system. This can either be a virtual private server which you’ve connected to with SSH or your local machine. Note that this tutorial was validated using a Linux server running Ubuntu 20.04, but the examples given should work on a computer running any version of any Linux distribution.
If you plan to use a remote server to follow this guide, we encourage you to first complete our Initial Server Setup guide. Doing so will set you up with a secure server environment — including a non-root user with sudo privileges and a firewall configured with UFW — which you can use to build your Linux skills.
The Terminal
The terms “terminal,” “shell,” and “command line interface” are often used interchangeably, but there are subtle differences between them:
- A terminal is an input and output environment that presents a text-only window running a shell.
- A shell is a program that exposes the computer’s operating system to a user or program. In Linux systems, the shell presented in a terminal is a command line interpreter.
- A command line interface is a user interface (managed by a command line interpreter program) which processes commands to a computer program and outputs the results.
When someone refers to one of these three terms in the context of Linux, they generally mean a terminal environment where you can run commands and see the results printed out to the terminal, such as this:
Becoming a Linux expert requires you to be comfortable with using a terminal. Any administrative task, including file manipulation, package installation, and user management, can be accomplished through the terminal. The terminal is interactive: you specify commands to run and the terminal outputs the results of those commands. To execute any command, you type it into the prompt and press ENTER.
When accessing a cloud server, you’ll most often be doing so through a terminal shell. Although personal computers that run Linux often come with the kind of graphical desktop environment familiar to most computer users, it is often more efficient or practical to perform certain tasks through commands entered into the terminal.
The Filesystem Hierarchy Standard
Nearly all Linux distributions are compliant with a universal standard for filesystem directory structure known as the Filesystem Hierarchy Standard (FHS). The FHS defines a set of directories, each of which serve their own special function.
The forward slash (/) is used to indicate the root directory in the filesystem hierarchy defined by the FHS.
When a user logs in to the shell, they are brought to their own user directory, stored within /home/. This is referred to as the user’s home directory. The FHS defines /home/ as containing the home directories for regular users.
The root user has its own home directory specified by the FHS: /root/. Note that / is referred to as the “root directory”, and that it is different from root/, which is stored within /.
Because the FHS is the default filesystem layout on Linux machines, and each directory within it is included to serve a specific purpose, it simplifies the process of organizing files by their function.
