This tutorial, which is the first in a series that teaches Linux fundamentals, covers getting started with the terminal, the Linux command line, and executing commands. If you are new to Linux, you will want to familiarize yourself with the terminal, as it is the standard way to interact with a Linux server.
If you would like to get the most out of this tutorial, you will need a Linux server to connect to and use. If you do not already have one, you can quickly spin one up by following this link: How To Create A DigitalOcean Droplet. This tutorial is written for an Ubuntu 22.04 server but the general principles apply to any other distribution of Linux.
Let’s get started by going over what a terminal emulator is.
A terminal emulator is a program that allows the use of the terminal in a graphical environment. As most people use an OS with a graphical user interface (GUI) for their day-to-day computer needs, the use of a terminal emulator is a necessity for most Linux server users.
Here are some free, commonly-used terminal emulators by operating system:
Each terminal emulator has its own set of features. In general, you should expect a modern terminal emulator to support tabbed windows and text highlighting.
In a Linux system, the shell is a command-line interface that interprets a user’s commands and script files, and tells the server’s operating system what to do with them. There are several shells that are widely used, such as the Bourne-Again shell (
bash) and Z shell (
zsh). Each shell has its own feature set and intricacies regarding how commands are interpreted, but they all feature input and output redirection, variables, and condition-testing, among other things.
This tutorial was written using the Bourne-Again shell, usually referred to as
bash, which is the default shell for most Linux distributions, including Ubuntu, Fedora, and RHEL.
When you first login to a server, you will typically be greeted by the Message of the Day (MOTD), which is typically an informational message that includes miscellaneous information such as the version of the Linux distribution that the server is running. After the MOTD, you will be dropped into the command prompt, or shell prompt, which is where you can issue commands to the server.
The information that is presented at the command prompt can be customized by the user, but here is an example of the default Ubuntu 20.04 command prompt:
Here is a breakdown of the composition of the command prompt:
sammy: The username of the current user
webapp: The hostname of the server
~: The current directory. In
bash, which is the default shell, the
~, or tilde, is a special character that expands to the path of the current user’s home directory; in this case, it represents
$: The prompt symbol. This denotes the end of the command prompt, after which the user’s keyboard input will appear
Here is an example of what the command prompt might look like, if logged in as
root and in the
Note that the symbol that ends the command prompt is a
#, which is the standard prompt symbol for
root. In Linux, the
root user is the superuser account, which is a special user account that can perform system-wide administrative functions. It is an unrestricted user that has permission to perform any task on a server.
Commands can be issued at the command prompt by specifying the name of an executable file, which can be a binary program or a script. There are many standard Linux commands and utilities that are installed with the OS, that allow you to navigate the file system, install and software packages, and configure the system and applications.
An instance of a running command is known as a process. When a command is executed in the foreground, which is the default way that commands are executed, the user must wait for the process to finish before being returned to the command prompt, at which point they can continue issuing more commands.
It is important to note that almost everything in Linux is case-sensitive, including file and directory names, commands, arguments, and options. If something is not working as expected, double-check the spelling and case of your commands!
Here are a few examples that will cover the fundamentals of executing commands.
Note: If you’re not already connected to a Linux server, now is a good time to log in. If you have a Linux server but are having trouble connecting, follow this link: How to Connect to Your Droplet with SSH.
To run a command without any arguments or options, type in the name of the command and press
If you run a command like this, it will exhibit its default behavior, which varies from command to command. For example, if you run the
cd command without any arguments, you will be returned to your current user’s home directory. The
ls command will print a listing of the current directory’s files and directories. The
ip command without any arguments will print a message that shows you how to use the
Try running the
ls command with no arguments to list the files and directories in your current directory (there may be none):
Many commands accept arguments, or parameters, which can affect the behavior of a command. For example, the most common way to use the
cd command is to pass it a single argument that specifies which directory to change to. For example, to change to the
/usr/bin directory, where many standard commands are installed, you would issue this command:
cd component is the command, and the first argument
/usr/bin follows the command. Note how your command prompt’s current path has been updated.
Try running the
ls command to see the files that are in your new current directory.
Output… grub-mkrescue sdiff zgrep grub-mkstandalone sed zipdetails grub-mount see zless grub-ntldr-img select-editor zmore grub-render-label semver znew grub-script-check sensible-browser
Most commands accept options, also known as flags or switches, that modify the behavior of the command. Options follow a command, and are indicated by a single
- character followed by one or more options, which are represented by individual upper- or lower-case letters. Some multi-word options can start with
--, followed by the flag text.
For an example of how options work, let’s look at the
ls command. Here are a couple of common options that come in handy when using
-l: print a “long listing”, which includes extra details such as permissions, ownership, file sizes, and timestamps
-a: list all of a directory’s files, including hidden ones (that start with
To use the
-l flag with
ls, use this command:
- ls -l
Note that the listing includes the same files as before, but with additional information about each file.
As mentioned earlier, options can often be grouped together. If you want to use the
-a option together, you could run
ls -l -a, or just combine them like in this command:
- ls -la
Note that the listing includes the hidden
.. directories in the listing, because of the
Options and arguments can almost always be combined, when running commands.
For example, you could check the contents of
/home, regardless of your current directory, by running this
ls -la /home
ls is the command,
-la are the options, and
/home is the argument that indicates which file or directory to list. This should print a detailed listing of the
/home directory, which should contain the home directories of all of the normal users on the server.
Environment variables are named values that are used to change how commands and processes are executed. When you first log in to a server, several environment variables will be set according to a few configuration files by default.
To view all of the environment variables that are set for a particular terminal session, run the
There will likely be a lot of output. Look for the
PATH environment variable is a colon-delimited list of directories where the shell will look for executable programs or scripts when a command is issued. For example, the
env command is located in
/usr/bin, and you are able to run it without specifying its full path because its path is in the
PATH environment variable.
The value of an environment variable can be retrieved by prefixing the variable name with a
$. This will expand the referenced variable to its value.
For example, to print out the value of the
PATH variable, you may use the
Or you could use the
HOME variable, which is set to your user’s home directory by default, to change to your home directory like this:
If you try to access an environment variable that hasn’t been set, it will be expanded to nothing; an empty string.
Now that you know how to view your environment variables, you should learn how to set them.
To set an environment variable, all you need to do is start with a variable name, followed immediately by an
= sign, followed immediately by its desired value:
Note that if you set an existing variable, the original value will be overwritten. If the variable did not exist in the first place, it will be created.
Bash includes a command called
export which exports a variable so it will be inherited by child processes. This allows you to use scripts that reference an exported environment variable from your current session.
You can also reference existing variables when setting a variable. For example, if you installed an application to
/opt/app/bin, you could add that directory to the end of your
PATH environment variable with this command:
Now verify that
/opt/app/bin has been added to the end of your
PATH variable with
Keep in mind that setting environment variables in this way only sets them for your current session. This means if you log out or otherwise change to another session, the changes you made to the environment will not be preserved. There is a way to permanently change environment variables, but this will be covered in a later tutorial.
Now that you have begun to learn about the Linux terminal (and a few commands), you should have a good foundation for expanding your knowledge of Linux commands. Read the next tutorial in this series to learn how to navigate, view, and edit files and their permissions.
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If you are new to Linux and its command line interface, it may seem like a daunting task to get started with it. This series will bring you up to speed with essential Linux basics, and provide a solid foundation for working with Linux servers. If you have little to no knowledge about using Linux, this is where you will want to start.
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