Glossary

100 terms that recur across the curriculum. Skim before starting; refer back as needed.

.bashrc

Script that runs every time you open a terminal - customize your environment

/dev

Device files representing hardware (disks, terminals, etc.)

/etc

Configuration files for system and applications

/etc/passwd

File containing user account information (not actual passwords)

/home

User home directories - your personal files live here

/var

Variable data - logs, caches, temporary files

/var/log

Directory containing log files for system and applications

~/.ssh/config

Configuration file for SSH connection shortcuts

Absolute Path

Full path from root: /home/user/file.txt

Activities

Top-left corner button to search apps, files, and switch windows

allow/deny

Firewall actions: allow permits traffic, deny blocks it

apt install

Download and install software packages

apt remove

Uninstall packages but keep configuration files

apt update

Command to refresh package list from repositories

Background Jobs

Processes running in background with & - terminal remains usable

cd

Change Directory - move to different folder

chmod

Change mode - command to modify file permissions using octal notation

chown

Change owner - command to change file ownership (requires root)

Commands

Instructions you type to tell the computer what to do

cp -r

Copy recursively - copies directories and all their contents

curl/wget

Command-line tools for downloading files from the internet

Customization

Linux lets you change everything; macOS/Windows limit modifications

daemon

Background service that runs without user interaction (like sshd, nginx)

Default Policy

What happens to traffic if no rule matches - usually deny

Device Drivers

Kernel modules that translate between hardware and OS abstractions

dig

DNS lookup tool - query nameservers for domain information

dmesg

Display kernel ring buffer - hardware and driver messages

DNS

Domain Name System - converts names like google.com to IP addresses

dpkg

Low-level package manager - apt uses this underneath

EFI Partition

512MB FAT32 partition that stores bootloader for UEFI systems

enable/disable

Control boot behavior - enable starts service at boot, disable prevents it

export

Make variable available to child processes - creates environment variable

ext4

Fourth Extended Filesystem - default Linux filesystem, journaled and reliable

FHS

Filesystem Hierarchy Standard - consistent layout across Linux distributions

Flags

Options that modify command behavior, like -l in 'ls -l'

for/while

Loops - repeat commands multiple times with different values

Functions

Reusable blocks of code with parameters - like mini-programs

GNOME

Default Ubuntu desktop environment - clean, modern graphical interface

GNU

GNU's Not Unix - recursive acronym for project creating free Unix-like tools

GPL License

GNU General Public License - ensures software remains free and improvements are shared

GPL vs Proprietary

GPL = open source, free to modify; Proprietary = closed, controlled by company

GRUB

GRand Unified Bootloader - shows OS selection menu at startup

if/then

Conditional execution - run code only if condition is true

ip addr

Modern command to show network interfaces and IP addresses

iptables

Low-level Linux firewall - ufw is a frontend for this

journalctl

Query systemd journal - view logs for services and system events

Kernel

Core of the OS that manages hardware and provides services to programs

kill -9

Force kill process - SIGKILL signal, cannot be ignored

Linus Torvalds

Finnish student who created the Linux kernel in 1991 as a hobby project

ln -s

Create symbolic link - like a shortcut to another file

Log Priorities

Severity levels: debug, info, notice, warning, error, critical

ls -la

List all files including hidden ones with detailed information

man pages

Manual pages - documentation for every Linux command

mkdir

Make directory - create new folders in filesystem

Monolithic

Kernel architecture where drivers run in kernel space for better performance

mv

Move or rename files - changes location or name

Octal Notation

Base-8 number system for permissions: r=4, w=2, x=1. Example: 755 = rwxr-xr-x

Open Source

Software with publicly available source code that anyone can study and modify

Owner/Group/Others

Three permission classes: file owner, group members, everyone else

Package Managers

Tools for installing software: apt (Ubuntu), brew (macOS), Windows Store

PATH

Environment variable listing directories where executable programs are found

PID

Process ID - unique number identifying each running program

ping

Test network connectivity by sending packets to a host

Port Filtering

Block or allow network traffic on specific ports

printenv

Print all environment variables - see what's configured

Prompt

Command interpreter showing username, hostname, and current directory

ps aux

List all processes with detailed information

pwd

Print Working Directory - shows your current location in filesystem

Relative Path

Path from current directory: ../file.txt or ./folder/file.txt

Repositories

Servers hosting software packages - Ubuntu's app store

rm -rf

Remove recursively and force - deletes directories and contents (dangerous!)

Root (/)

Top of filesystem hierarchy - everything starts here

Root Access

Linux gives full system control; macOS/Windows restrict for security

rwx

Read, Write, Execute permissions - the three actions you can control

scp

Secure Copy - copy files between computers over SSH

Shebang

#!/bin/bash at top of script - tells system which interpreter to use

Shrink Partition

Reduce Windows partition size to create free space for Ubuntu

source

Execute script in current shell - apply .bashrc changes without restart

ssh

Secure Shell - encrypted remote access to another computer

ssh-agent

Holds private keys in memory so you don't re-enter passphrase

ssh-keygen

Generate SSH key pairs for passwordless authentication

start/stop/restart

Control service state - start begins, stop ends, restart does both

sudo

SuperUser DO - temporarily run command as root with elevated privileges

Super Key

Windows key on keyboard - opens Activities overview

Swap

Disk space used as virtual RAM when physical memory is full

System Calls

API that programs use to request kernel services (open, read, write, etc.)

systemctl

System control - command to manage services on systemd-based Linux

Tab Completion

Press Tab to autocomplete file/command names - huge time saver

tail -f

Follow file in real-time - shows new lines as they're written

Terminal

Command-line interface where you type text commands

top/htop

Real-time process viewer - see CPU/memory usage live

touch

Create empty file or update timestamp of existing file

Transparency

Linux shows exactly what it's doing; others hide system internals

ufw

Uncomplicated Firewall - simple interface for managing firewall rules

UID/GID

User ID and Group ID - numerical identifiers for users and groups

Unix

Original operating system created at Bell Labs in 1969, grandfather of Linux

User Space

Protected area where applications run without direct hardware access

useradd

Command to create new user accounts on the system

usermod

Modify existing user accounts - change groups, home directory, shell

Variables

Named storage for values - no spaces around = sign