Operating System Fundamentals: Linux & Command Line Basics

Comprehensive vocabulary flashcards covering Linux history, kernel structure, UNIX distributions, networking concepts, shell commands, and text processing utilities.

Kernel (Linux)

The core component of the operating system loaded at boot that directly controls hardware (such as keyboard, mouse, disk, and network) and manages processes, memory, and files.

System Architecture Schematic (Linux/GNU)

A layered model showing computer architecture hardware (processor, memory, devices) managed by the Linux kernel, which interfaces with user space applications, compilers (gcc), and shells (bash).

UNIX Taxonomy Chart

A structural classification of UNIX operating systems divided into Proprietary lines (AIX, SunOS, HP/UX) and Open Source lines (GNU/Linux, BSD), with GNU/Linux further branching into distributions like Debian, Red Hat, and Slackware.

Ken Thompson and Dennis Ritchie

The computer scientists who created UNIX and developed the C programming language in 1969.

Richard Stallman

The founder of the GNU Project and open-source software movement between 1985 and 1989.

Andrew S. Tanenbaum

The creator of Minix in 1987, a minimalist educational operating system that influenced the creation of Linux.

Linus Torvalds

The developer who created and announced the Linux kernel on August 25, 1991.

GNU General Public License (GPL)

A free software license granting four core freedoms: freedom 0 (run for any purpose), freedom 1 (study and adapt source code), freedom 2 (redistribute copies), and freedom 3 (improve and release improvements).

Red Hat Enterprise Linux (RHEL)

A production-ready, commercially supported Linux distribution widely used as an enterprise platform for open-source computing.

Headless Server

A server operating without attached monitor, keyboard, or mouse hardware, managed entirely across a network using remote shell commands.

IPv4 Address

A 32-bit network address format consisting of four decimal numbers separated by dots, each ranging from 0 to 255 (e.g., 192.168.1.10).

IPv6 Address

A 128-bit network address format consisting of eight groups of hexadecimal digits separated by colons (e.g., 2001:0db8:85a3::8a2e:0370:7334).

Loopback Address (127.0.0.1)

A specialized IPv4 address used by a system to establish network communication back to itself on the local host.

Domain Name Server (DNS)

A network service that acts like a dictionary to translate human-readable domain hostnames (e.g., www.kdg.be) into numeric IP addresses.

Secure Shell (SSH)

A network protocol running on port 22 that enables encrypted, text-based remote login and command administration on a remote system.

Default Bash Prompt

A command-line prompt structured as username@hostname:current_directory$ where a $ represents a regular user and a # represents the root user.

Command Syntax Breakdown

The standard structure of a shell command composed of three space-separated elements: command name, option(s), and argument(s).

file (command)

A Linux utility command used to determine and output the file type of a given file independently of its extension.

stat (command)

A command that displays detailed metadata for a file or directory, including byte size on disk and access, modified, changed, and birth timestamps.

cat (command)

A Linux utility (short for concatenate) used to display the complete text contents of a file directly to standard output.

less (command)

A terminal pager command that displays text file contents screen-by-screen, supporting both forward and backward navigation with arrow keys.

head (command)

A command used to output the beginning lines of a text file, defaulting to 10 lines unless specified otherwise with -n.

tail (command)

A command used to output the ending lines of a text file, defaulting to 10 lines or modified with options like -n or -n+.

wc (command)

A word count utility command that tallies lines (-l), words (-w), bytes (-c), or characters (-m) in a text file.

Command Separator (;)

A semicolon character in bash that enables multiple distinct commands to be typed and executed sequentially on a single line.

Line Continuation Character ()

A trailing backslash symbol entered at the end of a line in bash to split a single long command across multiple physical lines.

history (command)

A bash command that lists previously executed terminal commands, which can be cleared completely using history -c.

Keyboard Shortcut ctrl-C

A key combination in the terminal used to send an interrupt signal that stops the execution of the currently running command.

Keyboard Shortcut ctrl-D

A key combination in the terminal that sends an end-of-file (EOF) marker to terminate input or exit the active shell session.

Keyboard Shortcut ctrl-R

A key combination in bash that triggers an interactive reverse search through previously executed commands in history.

whoami (command)

A command that outputs the effective user name of the currently logged-in user in the terminal session.

date (command)

A command that displays or formats system date and time using specifiers like +%R (time) or +%x (local date format).

RH124

The official course identifier for Red Hat System Administration I, focusing on core administration competences.

df (command)

A Linux utility command used to check file system disk space usage, commonly combined with -h or --human-readable.

free (command)

A Linux utility command that displays available and used physical RAM and swap memory space on the system.

uptime (command)

A Linux command showing how long the system has been continuously running, supporting readable output with -p or --pretty.