# Linux Basics # Welcome to week 2; introduction to linux Welcome back! We have another important topic to explore. Previously, you learned aboutoperating systems and user interfaces. You learned how operating systems work and how resources are allocated in computers. We also reviewed several common operating systems. You may already have a favorite operating system. It's common to hear that people are fans of one over another, but in the security world, Linux is commonly used. In this section, you'll be learning more about the Linux operating system and how it's used in everyday tasks in security. First, you'll learn about the architecture of Linux. After this, we'll compare the different distributions of Linux that are available. Lastly, you'll explore the shell, a key Linux component that allows you to communicate with the system. I remember when I first learned about the Linux OS, and I'm really happy to explore it with you now. # Introduction to Linux
# Linux architecture
# Linux architecture explained Understanding the Linux architecture is important for a security analyst. When you understand how a system is organized, it makes it easier to understand how it functions. In this reading, you’ll learn more about the individual components in the Linux architecture. A request to complete a task starts with the user and then flows through applications, the shell, the Filesystem Hierarchy Standard, the kernel, and the hardware. ## User The **user** is the person interacting with a computer. They initiate and manage computer tasks. Linux is a multi-user system, which means that multiple users can use the same resources at the same time. ## Applications An **application** is a program that performs a specific task. There are many different applications on your computer. Some applications typically come pre-installed on your computer, such as calculators or calendars. Other applications might have to be installed, such as some web browsers or email clients. In Linux, you'll often use a package manager to install applications. A **package manager** is a tool that helps users install, manage, and remove packages or applications. A **package** is a piece of software that can be combined with other packages to form an application. ## Shell The **shell** is the command-line interpreter. Everything entered into the shell is text based. The shell allows users to give commands to the kernel and receive responses from it. You can think of the shell as a translator between you and your computer. The shell translates the commands you enter so that the computer can perform the tasks you want. ## Filesystem Hierarchy Standard (FHS) The **Filesystem Hierarchy Standard (FHS)** is the component of the Linux OS that organizes data. It specifies the location where data is stored in the operating system. A **directory** is a file that organizes where other files are stored. Directories are sometimes called “folders,” and they can contain files or other directories. The FHS defines how directories, directory contents, and other storage is organized so the operating system knows where to find specific data. ## Kernel The **kernel** is the component of the Linux OS that manages processes and memory. It communicates with the applications to route commands. The Linux kernel is unique to the Linux OS and is critical for allocating resources in the system. The kernel controls all major functions of the hardware, which can help get tasks expedited more efficiently. ## Hardware The **hardware** is the physical components of a computer. You might be familiar with some hardware components, such as hard drives or CPUs. Hardware is categorized as either peripheral or internal. ### **Peripheral devices** **Peripheral devices** are hardware components that are attached and controlled by the computer system. They are not core components needed to run the computer system. Peripheral devices can be added or removed freely. Examples of peripheral devices include monitors, printers, the keyboard, and the mouse. ### **Internal hardware** **Internal hardware** are the components required to run the computer. Internal hardware includes a main circuit board and all components attached to it. This main circuit board is also called the motherboard. Internal hardware includes the following:
- The **Central Processing Unit (CPU)** is a computer’s main processor, which is used to perform general computing tasks on a computer. The CPU executes the instructions provided by programs, which enables these programs to run. - **Random Access Memory (RAM)** is a hardware component used for short-term memory. It’s where data is stored temporarily as you perform tasks on your computer. For example, if you’re writing a report on your computer, the data needed for this is stored in RAM. After you’ve finished writing the report and closed down that program, this data is deleted from RAM. Information in RAM cannot be accessed once the computer has been turned off. The CPU takes the data from RAM to run programs. - The **hard drive** is a hardware component used for long-term memory. It’s where programs and files are stored for the computer to access later. Information on the hard drive can be accessed even after a computer has been turned off and on again. A computer can have multiple hard drives.
## Key takeaways It’s important for security analysts to understand the Linux architecture and how these components are organized. The components of the Linux architecture are the user, applications, shell, Filesystem Hierarchy Standard, kernel, and hardware. Each of these components is important in how Linux functions. # Linux distributions
# KALI LINUX ™
# More Linux distributions Previously, you were introduced to the different distributions of Linux. This included KALI LINUX ™. (KALI LINUX ™ is a trademark of OffSec.) In addition to KALI LINUX ™, there are multiple other Linux distributions that security analysts should be familiar with. In this reading, you’ll learn about additional Linux distributions. ## KALI LINUX ™ **KALI LINUX ™** is an open-source distribution of Linux that is widely used in the security industry. This is because KALI LINUX ™, which is Debian-based, is pre-installed with many useful tools for penetration testing and digital forensics. A **penetration test** is a simulated attack that helps identify vulnerabilities in systems, networks, websites, applications, and processes. **Digital forensics** is the practice of collecting and analyzing data to determine what has happened after an attack. These are key activities in the security industry. However, KALI LINUX ™ is not the only Linux distribution that is used in cybersecurity. ## Ubuntu **Ubuntu** is an open-source, user-friendly distribution that is widely used in security and other industries. It has both a command-line interface (CLI) and a graphical user interface (GUI). Ubuntu is also Debian-derived and includes common applications by default. Users can also download many more applications from a package manager, including security-focused tools. Because of its wide use, Ubuntu has an especially large number of community resources to support users. Ubuntu is also widely used for cloud computing. As organizations migrate to cloud servers, cybersecurity work may more regularly involve Ubuntu derivatives. ## Parrot **Parrot** is an open-source distribution that is commonly used for security. Similar to KALI LINUX ™, Parrot comes with pre-installed tools related to penetration testing and digital forensics. Like both KALI LINUX ™ and Ubuntu, it is based on Debian. Parrot is also considered to be a user-friendly Linux distribution. This is because it has a GUI that many find easy to navigate. This is in addition to Parrot’s CLI. ## Red Hat® Enterprise Linux® **Red Hat Enterprise Linux** is a subscription-based distribution of Linux built for enterprise use. Red Hat is not free\*, which is a major difference from the previously mentioned distributions. Because it’s built and supported for enterprise use, Red Hat also offers a dedicated support team for customers to call about issues. with my personal experience, you can use RHEL9 for personal use. also as of July of 2023, its parent company may be trying to break copyright law by limiting access to source code, and close sourcing the project. if they succeed many other distros might die or become less secure or die, like centOS. I likely wont update this but you can google it yourself to see how that went. ## CentOS **CentOS** is an open-source distribution that is closely related to Red Hat. It uses source code published by Red Hat to provide a similar platform. However, CentOS does not offer the same enterprise support that Red Hat provides and is supported through the community. p.s. CentOS may be dead because its parent company is trying to kill it at the time of posting this page, google it to see if it has died LOL ### Arch Linux **Arch Linux** is an open-source distribution known for its simplicity and user-focused design. It adheres to the "Keep It Simple, Stupid" (KISS) principle, offering a minimal base system that users can customize to their needs, reducing potential security risks, provides more control over the system, rolling-release model ensures up-to-date security updates. A key feature is the Arch User Repository (AUR), a community-driven repository that lets users compile and install packages from source using the Arch package manager, pacman. ## Key takeaways KALI LINUX ™, Ubuntu, Parrot, Red Hat, and CentOS are all widely used Linux distributions. It’s important for security analysts to be aware of these distributions that they might encounter in their career. # Package managers for installing applications Previously, you learned about Linux distributions and that different distributions derive from different sources, such as Debian or Red Hat Enterprise Linux distribution. You were also introduced to package managers, and learned that Linux applications are commonly distributed through package managers. In this reading, you’ll apply this knowledge to learn more about package managers. ## Introduction to package managers A **package** is a piece of software that can be combined with other packages to form an application. Some packages may be large enough to form applications on their own. Packages contain the files necessary for an application to be installed. These files include dependencies, which are supplemental files used to run an application. Package managers can help resolve any issues with dependencies and perform other management tasks. A **package manager** is a tool that helps users install, manage, and remove packages or applications. Linux uses multiple package managers. **Note:** It’s important to use the most recent version of a package when possible. The most recent version has the most up-to-date bug fixes and security patches. These help keep your system more secure. ## Types of package managers Many commonly used Linux distributions are derived from the same parent distribution. For example, KALI LINUX ™, Ubuntu, and Parrot all come from Debian. CentOS comes from Red Hat. This knowledge is useful when installing applications because certain package managers work with certain distributions. For example, the Red Hat Package Manager (RPM) can be used for Linux distributions derived from Red Hat, and package managers such as dpkg can be used for Linux distributions derived from Debian. Different package managers typically use different file extensions. For example, Red Hat Package Manager (RPM) has files which use the .rpm file extension, such as Package-Version-Release\_Architecture.rpm. Package managers for Debian-derived Linux distributions, such as dpkg, have files which use the .deb file extension, such as Package\_Version-Release\_Architecture.deb. ## Package management tools In addition to package managers like RPM and dpkg, there are also package management tools that allow you to easily work with packages through the shell. Package management tools are sometimes utilized instead of package managers because they allow users to more easily perform basic tasks, such as installing a new package. Two notable tools are the Advanced Package Tool (APT) and Yellowdog Updater Modified (YUM). ### **Advanced Package Tool (APT)** APT is a tool used with Debian-derived distributions. It is run from the command-line interface to manage, search, and install packages. ### **Yellowdog Updater Modified (YUM)** YUM is a tool used with Red Hat-derived distributions. It is run from the command-line interface to manage, search, and install packages. YUM works with .rpm files. ## Key takeaways A package is a piece of software that can be combined with other packages to form an application. Packages can be managed using a package manager. There are multiple package managers and package management tools for different Linux distributions. Package management tools allow users to easily work with packages through the shell. Debian-derived Linux distributions use package managers like dpkg as well as package management tools like Advanced Package Tool (APT). Red Hat-derived distributions use the Red Hat Package Manager (RPM) or tools like Yellowdog Updater Modified (YUM). # Vanilla os i came accross vanilla os in a yt video and it appears to be realy interesting. i quite like gnome as a base and im thinking this is potentially one of the best options in the future if they stick with it. also theres only two updates per year and a roling release but you have to manually enable rolling releases tl;dr its stable asf, and you can run any app on it! **Vanilla OS: A Unique Solution to Distro Hopping and the Future of Software Installation** Vanilla OS is a Linux distribution that aims to resolve the common practice of distro hopping. This term refers to the habit among Linux users of switching between different Linux distributions to find the perfect balance of stability, hardware support, and application access. Vanilla OS offers all these features within a single, highly stable base. What sets Vanilla OS apart is its approach to software installation. It introduces 'apx', a package manager that allows software installation from any source by installing them onto distro containers. This means that Vanilla OS can run virtually any software developed for Linux, effectively addressing the issue of distro packaging fragmentation. This unique combination of features positions Vanilla OS as a potential game-changer in the Linux ecosystem. **Intuitive User Experience** Vanilla OS prioritizes user-friendliness in its design. The intuitive installer guides users through the necessary steps, and post-installation, users can customize their experience, choosing between dark and light mode, enabling support for Flatpak and AppImage, and selecting their preferred apps. This user-centric approach makes Vanilla OS accessible to both beginners and technically inclined users. **Immutability and Atomicity: Enhancing Security and Stability** One of the distinguishing features of Vanilla OS is its immutable and atomic nature. The base system is locked down, preventing both applications and users from writing to it, except for certain directories like the home folder or partition and the /etc and /var directories. This design principle significantly bolsters the system's security. Updates in Vanilla OS are applied atomically, meaning each update either completes successfully or, if any issue arises, the entire operation is reverted, leaving the system unaltered. This ensures that any reboot will either return the system to its previous state or update it successfully. **Is Vanilla OS the Future of Linux Distributions?** Vanilla OS represents a promising concept that could potentially shape the future of Linux distributions. It provides access to virtually all Linux-developed software at native speeds within a highly stable base. However, it's not a one-size-fits-all solution. Users who only need software from FlatHub may not require Vanilla OS, and those unfamiliar with the command line or the concept of containers might find it challenging to use. However, with further development, such as a graphical layer on 'apx' for intuitive software installation from containers, Vanilla OS could become an optimal solution for users seeking extensive software access without compromising system stability for anyone who cares this one was written with ai, modified by me... # Nix OS make page on nix os, alternative to vanilla os? # Resources for completing Linux labs This course features hands-on lab activities where you’ll have the opportunity to practice Linux commands in the terminal. You’ll use a platform called Qwiklabs to complete these labs. In this reading, you’ll learn how to use Qwiklabs. This reading first provides a section on how to use Qwiklabs, which includes details on how to launch a lab, how to interact within the Qwiklabs environment, and how to end a lab. This is followed by another section on helpful navigation tips and keyboard shortcuts; these may be useful when working in the terminal. **Note**: You will not launch Qwiklabs directly from this reading and instead will do this through lab activities and exemplars that you encounter throughout the course. Im not posting the Qwiklabs, this is just how to use Qwiklabs, and if you use Qwiklabs thats on you. ## How to use Qwiklabs ### **Launching Qwiklabs** When you select a lab, you start from a Coursera page. You will need to click **Launch App** on that page. After you click **Launch App**, a new tab will open with a Qwiklabs page that contains instructions for that particular lab. ### **Start Lab button** On the Qwiklabs page, you must click **Start Lab** to open a temporary terminal. The instructions for the lab will move to the right side of the screen.
![Green button with text “Start Lab” and a maximum time limit of 20 minutes displayed.](https://d3c33hcgiwev3.cloudfront.net/imageAssetProxy.v1/bbLYK8KXTheEmp-pArlF-g_ef7afc94b9304f30844a19e45e922ff1_wPU2KdBxIZhEA0euFsDlhs_nHve2ceZ69LNUPx4ZE0Bb8jVXhx-Qq2dfRIK1a8IFwZ08_GkPEgh4NR_8yvGYvn0U4FTm6l8QGhpbBlTwXew2thU31_64Ivi7nwPKJNCtemriZhtJWAfZdc0dQ-tTfEo?expiry=1688688000000&hmac=Xs_PR-pKuEqZUuDwbTvXOG4xEqxiu8fZfNRcFei0SYc)
Read the instructions and complete all the tasks in the lab by entering commands in the terminal. **Note**: It may take a moment for the terminal to start. ### **Lab control dialog box** After you click **Start Lab**, the lab control dialog box opens. It contains the **End Lab** button, the **timer**, and the **Open Linux Console** button. You can hide or unhide the dialog box by clicking the following icon in the red box:
![Four rectangles spiraling next to each other to comprise one square surrounded by a red box in a screenshot of the lab.](https://d3c33hcgiwev3.cloudfront.net/imageAssetProxy.v1/9J3KUOFWRNWzekD6Uiykyg_f489a579c31c4a8b8c2f9b68467495f1_LuMypehj-sqYyJlYCJGk-0LPWQirKP_cVeCYhsw1ism9amvqsYDhZEdh-Wyzh1tW__cut8UToAifaNs6LRj3iXCr4ujUo_RA7h-qx4rJVs1CRjAwAwCGM-gnKcx4wIWeV2b9IqCRB14qOVyda1LeQDA?expiry=1688688000000&hmac=sUwVJcuIGXiK6OC-T6cB8nckcTeHRtnugLt3Wh56lAI)
### **The timer** The **timer** starts when the terminal has loaded. The timer keeps track of the amount of time you have left to complete a lab. The timer counts down until it reaches 00:00:00. When it does, your temporary terminal and resources are deleted. You will have ample time to complete the labs. But, stay focused on completing the tasks to ensure you use your time well. ### **Open Linux Console button** When you click the button to **Open Linux Console**, the terminal opens in a new browser window:
![A red square around a button with text “Open Linux Console”.](https://d3c33hcgiwev3.cloudfront.net/imageAssetProxy.v1/GL_lszqoS_SwMddGbzYgEQ_1bd87af68f5f46a0be668b190f51f6f1_tEIGaT6dW10ie3BjpmzvFivoi8feEG9-Iw7O_lAjvdvWpFXlZOm8HmiNc2c9OgRKvKUBjJhp8HfoR3qu9JPY4GzGbCSOvh_nC-pKywu_G0B7V_ULMpjKTT06CYfx4b7oS1HPZnudcST_D-LjQmdIwmY?expiry=1688688000000&hmac=vwiCV0cQqzvmvDv9YdaDCvAWu2lfLxRHEr1NoC1gp4Y)
Use this feature if you want a full-screen view of the terminal. You can close this window at any time. Closing the window does not end your lab, and you can continue working in the terminal in the original tab. ### **Check progress** You can check your progress by clicking **Check my progress** at the end of each task.
![Blue button with text “Check my progress” below a sample task.](https://d3c33hcgiwev3.cloudfront.net/imageAssetProxy.v1/IbOfFeajT2q9yZWHyXxHOA_e8b0749220334c5aa3ac5f0aa7070ef1_kN58Isr_cUeyITXiw1gAqBQeWHP4UIaMnQbwyVY6sRQre_L0gtmYjALeqKvApc1L8XchdZeLsfUaNwA9aQZL0Kir1h0c8BJjGsKWq8mfHEmrS0pVNBb4h5c-3hJ-__kbwaa0LN5U8CbJBLlqWToABF0?expiry=1688688000000&hmac=z0DH9eRfFA4-sNQbkhRuP2m3aJnXx6AtSwQHrTRBNgs)
If you haven’t yet completed a task, you’ll receive hints on what you must do to complete it. You can click **Check my progress** whenever you want to check the completion status of a task or receive a hint. ### **Using copy/paste commands** The first time you try to use copy or paste keyboard shortcuts (such as **CTRL + C**), you’ll receive a pop-up requesting permission to use your device’s clipboard: “**googlecoursera.qwiklabs.com wants to see text and images copied to the clipboard.**” Please click **Allow** if you would like to be able to use these shortcuts in the Qwiklabs platform. If you choose not to allow Qwiklabs access to your clipboard, you cannot use keyboard shortcuts but you can still complete the lab. ### **Code block** Certain steps may include a code block. Click the copy button to copy the code provided and then paste it into the terminal.
![Two layered rectangles surrounded by a red box on the right side of a sample code block to indicate copy.](https://d3c33hcgiwev3.cloudfront.net/imageAssetProxy.v1/tSaH4Zd2T9qHv2ALlr1fGA_a4c26fdc722a4b3c8f38f12e15c863f1_OhCX3BSN-yf0Nd8lnjLLk4t5hUVBbpR913lAp_yIdqsaOEgDIiV-p9N2nflw4o4ED_Fwxsg6Dez7gopRSYphMueEEoblkkIBY3ELnRDiqKhC6ZILGCJH1NSugmPxU2Y50M2sGk98kdv--GwRMchPRJU?expiry=1688688000000&hmac=BbUXv1jOAecIBgkFxB-BNnArWB5Mh4cP64x510LU_bc)
To paste code or other text content that you have copied from the instructions into the terminal, activate the terminal by clicking anywhere inside it. The terminal is active when the cursor in the terminal changes from a static empty outline to a flashing solid block.
![A dollar sign prompt and white rectangle cursor surrounded by a red box in the terminal.](https://d3c33hcgiwev3.cloudfront.net/imageAssetProxy.v1/cgjBaqtES0ayrgvTCk3QZQ_25005fa6300f4d1ba01ef6a768097ef1_NCn3RU6ab8eSTxYYo2V1zh5y2ehRWaP-OavQGkZpJgxI-K-JeeIL5QSJCMqQqMQ-09eapv_GCAub7jZG6zmqX3VZ3Vx59qV_qXdJVo4LUqGW2kQz36DXIGk17rzkSmMmPvVRlrMp3nfeoC9dbYjk98Q?expiry=1688688000000&hmac=fzzGgVZjDG9kHsL4nqHgUnecySZzEBUaJTrxqO_hR0g)
Once the terminal is active, use the keyboard shortcut **CTRL + V** (hold down the **CTRL** key and press the **V** key) to insert the copied text into the terminal at the location of the flashing cursor. ### **Scrolling** In certain situations, you may want to scroll within the terminal window. To do so, use the scroll wheel on your mouse or the touchpad of your computer. ### **End Lab button**
![A red button with text “End Lab” surrounded by a red box.](https://d3c33hcgiwev3.cloudfront.net/imageAssetProxy.v1/dN9wPgYMQl2fBxFAffoZjw_38694553980f42cd94d8906a1f2d1bf1_Mfw27huMPvdOZI21TbioE29m49cakKuRkC3cEtNpIUkdnVMw7P8r1N9ETGXSSloVpG_zhsBqeA4uj7RTVMTFLChkhBUdF4yYkeIfa5Y42X6AWHf7HrQqiBm9sPcDBpY2pxdpvQVQRQSvbQbmCS43wY8?expiry=1688688000000&hmac=CNDm4LP82u_528axrzmV1g9S7A6blmUT64A0P6CbPX8)
Finally, click **End Lab** when you’ve completed the tasks in the lab. **Note**: Don't click **End Lab** until you're finished; you'll lose access to the work you've done throughout the lab. ### **Tracking progress on Coursera** If you complete a lab but your progress hasn’t been tracked on Coursera, you may need to refresh the page for your progress to be registered. Once you complete the lab and refresh the page, the green check mark should appear. ## Helpful navigation tips and keyboard shortcuts The following contains a list of navigation tips and keyboard shortcuts you may find useful when completing your Linux labs. Your cursor must be in the terminal window to use these navigation tips and keyboard shortcuts.
- CTRL + C: Terminates a command that is currently running; from the instructions portion of Qwiklabs, you can use CTRL + C to copy, but within the terminal, it will only terminate a command and if one isn't running, it will display ^C at the prompt - CTRL + V: Pastes text - clear: Clears the terminal screen; this can also be done by entering CTRL + L - CTRL + A: Sets your cursor at the beginning of a command - CTRL + E: Sets your cursor at the end of a command - Left arrow **key**: Moves left within a command - Right arrow **key**: Moves right within a command - Up arrow **key**: Provides the last command you entered into the command line; can be entered multiple times to go through multiple commands from the command history - Down arrow **key**: Provides the next command in the command history; must be after using the up arrow key - Tab **key**: Provides available suggestions for completing your text
## Key takeaways Knowing how to navigate Qwiklabs will be useful as you complete the labs throughout this course. These labs can help you practice what you’ve learned in an interactive environment. # Introduction to the shell
# Different types of shells Knowing how to work with Linux shells is an important skill for cybersecurity professionals. Shells can be used for many common tasks. Previously, you were introduced to shells and their functions. This reading will review shells and introduce you to different types, including the one that you'll use in this course. ## Communicate through a shell As you explored previously, the **shell** is the command-line interpreter. You can think of a shell as a translator between you and the computer system. Shells allow you to give commands to the computer and receive responses from it. When you enter a command into a shell, the shell executes many internal processes to interpret your command, send it to the kernel, and return your results. ## Types of shells The many different types of Linux shells include the following:
- Bourne-Again Shell (bash) - C Shell (csh) - Korn Shell (ksh) - Enhanced C shell (tcsh) - Z Shell (zsh) - PowerShell (by microsoft also on windows)
All Linux shells use common Linux commands, but they can differ in other features. For example, ksh and bash use the dollar sign ($) to indicate where users type in their commands. Other shells, such as zsh, use the percent sign (%) for this purpose. ## Bash **Bash** is the default shell in most Linux distributions. It’s considered a user-friendly shell. You can use bash for basic Linux commands as well as larger projects. Bash is also the most popular shell in the cybersecurity profession. You’ll use bash throughout this course as you learn and practice Linux commands. ## Key takeaways Shells are a fundamental part of the Linux operating system. Shells allow you to give commands to the computer and receive responses from it. They can be thought of as a translator between you and your computer system. There are many different types of shells, but the bash shell is the most commonly used shell in the cybersecurity profession. You’ll learn how to enter Linux commands through the bash shell later in this course. # Input and output in the shell
# Linux basics Wrap-up; Glossary terms from week 2
--- ## Terms and definitions from Course 4, Week 2 **Application:** A program that performs a specific task **Bash:** The default shell in most Linux distributions **CentOS:** An open-source distribution that is closely related to Red Hat **Central Processing Unit (CPU):** A computer’s main processor, which is used to perform general computing tasks on a computer **Command:** An instruction telling the computer to do something **Digital forensics:** The practice of collecting and analyzing data to determine what has happened after an attack **Directory:** A file that organizes where other files are stored **Distributions:** The different versions of Linux **File path:** The location of a file or directory **Filesystem Hierarchy Standard (FHS):** The component of the Linux OS that organizes data **Graphical user interface (GUI):** A user interface that uses icons on the screen to manage different tasks on the computer **Hard drive:** A hardware component used for long-term memory **Hardware**: The physical components of a computer **Internal hardware:** The components required to run the computer **Kali Linux ™**: An open-source distribution of Linux that is widely used in the security industry **Kernel:** The component of the Linux OS that manages processes and memory **Linux:** An open source operating system **Package:** A piece of software that can be combined with other packages to form an application **Package manager:** A tool that helps users install, manage, and remove packages or applications **Parrot:** An open-source distribution that is commonly used for security **Penetration test (pen test):** A simulated attack that helps identify vulnerabilities in systems, networks, websites, applications, and processes **Peripheral devices:** Hardware components that are attached and controlled by the computer system **Random Access Memory (RAM):** A hardware component used for short-term memory **Red Hat® Enterprise Linux®** (also referred to simply as Red Hat in this course)**:** A subscription-based distribution of Linux built for enterprise use **Shell:** The command-line interpreter **Standard error:** An error message returned by the OS through the shell **Standard input:** Information received by the OS via the command line **Standard output:** Information returned by the OS through the shell **String data:** Data consisting of an ordered sequence of characters **Ubuntu:** An open-source, user-friendly distribution that is widely used in security and other industries **User:** The person interacting with a computer