Week 1 Day 3 — NETW-0001 Operating Systems Fundamentals

0:00–0:10
Recap

0:10–0:40
Lecture

0:40–1:50
Lab 2 Pt 1–2

1:50–2:00
Debrief

0:00 – 0:10 Recap · 10 min

Verify desktop2 and collect research answers

Confirm desktop2 is fully installed and booting. Anyone who didn't finish gets 5 minutes now — start the VM and confirm it reaches the login screen. Both VMs must be working before Lab 2 begins.
Quickly call on two or three students for their Day 2 research: what is /var typically used for? What makes ext4 the standard choice for Linux partitions? What were the AI tool examples of Linux in the real world?
Ask: "In Windows, when you open File Explorer, you see C:\, D:\, etc. In Linux, what do you think you'd see instead?" Take answers — bridge to today's lecture on the filesystem hierarchy.

0:10 – 0:40 Lecture · 30 min

The terminal, TTY, the Linux filesystem hierarchy, and paths

Part 1 — Terminal vs. shell, and why bother (8 min)

Two separate things people call "the terminal": the terminal is the window or interface you type into. The shell is the program running inside it that interprets your commands. In Ubuntu, the default shell is bash (Bourne Again Shell). When you press Ctrl+Alt+T, you get a terminal emulator running bash.
Why use the CLI at all? Take a few guesses from the class, then fill in:
· Chain two commands together with a pipe — doing things the GUI simply cannot do
· Some switches and tools only work in the shell
· SSH sessions to remote servers have no GUI — the terminal is all you have
· Scripting and automation — the terminal is programmable
· Speed — once you know the commands, the keyboard is faster than the mouse for system tasks
TTY — what it actually is: TTY stands for TeleTYpewriter — a real physical terminal from the 1970s. Linux still models its terminal system on those devices. Ubuntu gives you 6 TTYs, accessed with Ctrl+Alt+F1 through F6. TTY1 and TTY2 are reserved for the graphical desktop (the X Window System running your GUI). TTY3 through TTY6 are pure text terminals — no GUI, no mouse, just a login prompt and bash. Bridge: this is like Windows Safe Mode with Command Prompt — a minimal text-only environment, but on Linux it's always there, always available, and doesn't require a special boot mode.

Part 2 — The Linux filesystem hierarchy (12 min)

Everything is one tree: In Windows, each drive gets a letter (C:\, D:\, F:\). In Linux, there is exactly one root: /. Everything — drives, USB sticks, network shares, even running processes — appears somewhere under /. Additional storage is "mounted" as a subdirectory, not given a new letter.
Draw the hierarchy on the board as you explain each directory. This is the same across virtually all Linux distributions:

Directory	Purpose	Windows equivalent
`/`	The root — top of the entire filesystem tree	C:\ (roughly)
`/bin`	Essential user binaries — ls, cp, mv, cat, grep. Must be available even in single-user mode	C:\Windows\System32 (partly)
`/sbin`	System binaries for admin tasks — fdisk, ifconfig, mount. Root-only tools	Elevated system utilities
`/home`	User home directories — /home/student, /home/alice, etc. Personal files live here	C:\Users\
`/root`	Home directory of the root user — separate from /home for security	C:\Users\Administrator
`/etc`	Configuration files — editable text files that control system and application behaviour	Registry (conceptually)
`/var`	Variable data — logs, mail, package manager data, print spool. Changes constantly	C:\Windows\Logs + C:\ProgramData
`/tmp`	Temporary files — cleared on reboot. World-writable	C:\Windows\Temp
`/usr`	User-installed programs and their support files — most applications live here	C:\Program Files
`/opt`	Optional/third-party software that doesn't follow standard layout	C:\Program Files (non-standard installs)
`/dev`	Device files — every hardware device appears as a file here. /dev/sda = first disk	No direct equivalent
`/proc`	Virtual filesystem — shows running processes and kernel info as files. Not on disk	Task Manager data, roughly
`/lib`	Shared libraries required by /bin and /sbin — like .dll files	C:\Windows\System32 .dll files
`/media`	Mount point for removable media — USB drives, DVDs auto-mount here	D:\ (removable drives)

Part 3 — Absolute vs. relative paths (10 min)

Absolute path: Starts with / — specifies the complete location from the root of the filesystem. It is always the same, regardless of where you currently are. Example: /home/student/lab2/notes.txt — this path works from anywhere on the system.
Relative path: Does not start with / — specifies a location relative to your current directory. Example: if you are currently in /home/student, then lab2/notes.txt refers to the same file. If you move to /etc, the same relative path lab2/notes.txt now points to /etc/lab2/notes.txt — which probably doesn't exist.
Special path shortcuts:
· ~ — your home directory (/home/student). cd ~ always takes you home.
· . — the current directory. ./script.sh means "run script.sh in the current directory."
· .. — the parent directory. cd .. goes up one level.
· - — the previous directory. cd - toggles between the last two locations.
Rule of thumb: Use absolute paths in scripts (they work regardless of where the script is run from). Use relative paths at the command line when navigating interactively (shorter to type). Bridge: Windows paths work the same way — C:\Users\Student is absolute, .\Documents is relative.

0:40 – 1:50 Lab 2 Parts 1–2 · 70 min

Lab 2 — The Terminal: TTY, navigation, and directory operations

All lab work today is on desktop1. Log in as student. The goal by end of session is confident navigation — moving around the filesystem, creating and removing directories, and understanding the difference between absolute and relative paths without having to think about it.

Part 1 — Terminals and TTY (15 min)

Log in to desktop1 as student. Open a terminal from the dock or with Ctrl+Alt+T. This is a virtual terminal — a terminal emulator running inside the GUI session.
Switch to a real TTY: press Ctrl+Alt+F3. The screen goes black and shows a login prompt — no GUI, no mouse. Log in as student. You are now in TTY3, a genuine text terminal.
Answer in your lab notes: How many real TTY terminals are there on this system? (Hint: try Ctrl+Alt+F1 through F6 — observe which ones are login prompts vs. GUI sessions. F1 and F2 will show the graphical desktop.)
In TTY3, run the command who. Record the output and explain what each column means in your lab notes. You should see at least two entries — your GUI session on TTY1 or TTY2, and your current TTY3 session.
Switch back to the GUI: press Ctrl+Alt+F2 (or F1). Verify your desktop is still there — the GUI session keeps running while you use TTYs. Return to your virtual terminal for the rest of the lab.

Key insight: The GUI is just another process running in a TTY. If the desktop crashes, Ctrl+Alt+F3 gets you to a working terminal to diagnose and fix it. This is one of the most practically useful things about Linux — you always have a way in.

Part 2 — Navigation and directory operations (55 min)

Where am I? In your virtual terminal, run pwd (print working directory). Record the output in your lab notes — this is your starting location. It should be /home/student. Every time you open a terminal, this is where you begin.
Create your lab directory: Run mkdir lab2. Verify it was created with ls. Note: mkdir creates the directory in your current location — you didn't need to specify the full path because you're already in /home/student.
Navigate to root and create a directory using an absolute path:
· Run cd / — you are now at the root of the filesystem.
· Create a directory inside lab2 using an absolute path: mkdir /home/student/lab2/documents2
· You created a directory in /home/student/lab2 without leaving /. That's the power of absolute paths.
· Verify: ls /home/student/lab2 — you should see documents2.
Navigate to /etc and create a directory using a relative path:
· Run cd /etc
· You need to create a "backups" directory inside /home/student/lab2. From /etc, the relative path is: ../../home/student/lab2
· Create it: mkdir ../../home/student/lab2/backups
· Verify from /etc: ls ../../home/student/lab2 — you should see both documents2 and backups.
· Record in your notes: how many ../ did you need and why?
Remove a directory:
· Run rmdir /home/student/lab2/documents2 to remove the documents2 directory.
· Verify it's gone: ls ~/lab2
· Note: rmdir only works on empty directories. Try creating a file inside a directory and then removing it with rmdir — observe the error. You will need rm -r for non-empty directories (covered in Part 4).
Return home and explore the ~ shortcut:
· Run cd ~ — you are back in /home/student.
· Run cd /var/tmp, then cd - — observe where you end up. cd - toggles between your last two locations.
Create a directory with a space in the name:
· Try: mkdir my docs — observe what happens. (It creates two directories: "my" and "docs".)
· Remove them both: rmdir my docs
· Create it correctly using quotes: mkdir "my docs"
· Or using an escape character: mkdir my\ docs
· Record in your lab notes: what is the absolute path of "my docs"? What is its relative path from /home/? What is its relative path from /var/tmp/?
Compare Windows dir vs. Linux ls:
· Change to the root: cd /
· Run ls — a simple listing of contents, colour-coded by type.
· Run ls -l — long format. For the /bin directory entry, record in your lab notes: Permissions · Owner · Group · Size · Date.
· Run ls -la — long format including hidden files (those starting with .).
· Run ls -lh — human-readable file sizes (KB, MB, GB instead of bytes).
· Bridge: dir in Windows is the rough equivalent of ls. But Linux flags give you far more control over the output.

⭐ Early finisher — OverTheWire Bandit Level 0

You now know enough to attempt Bandit Level 0. Open a terminal and run: ssh bandit0@bandit.labs.overthewire.org -p 2220 — password is bandit0
Level 0: the password for Level 1 is stored in a file called readme in the home directory. Find it and connect to bandit1. Record the password somewhere safe — you will need it to reconnect.
Level 1: the password is in a file called - (a dash). How do you read a file with that name? Think about how the shell interprets a leading dash...

1:50 – 2:00 Debrief · 10 min

Paths, TTY, and what's coming tomorrow

Quick check: write a path challenge on the board. Given: current directory is /var/log. Target: /home/student/lab2/backups. Ask for the relative path — take hands. Answer: ../../home/student/lab2/backups. Ask for the absolute — anyone: /home/student/lab2/backups. Point out that the absolute is always the same; the relative changes depending on where you are.
Ask: "What happened when you tried to mkdir my docs without quotes?" — two directories. This is why spaces in filenames are annoying in Linux. Convention: use underscores or hyphens in filenames. You'll thank yourself later when scripting.
Preview Day 4: Tomorrow — searching the filesystem with find, searching file contents with grep, and creating and manipulating text files. These are the three commands that make the Linux terminal genuinely powerful for a sysadmin. Also: why sudo exists, and when to use it.

Learning outcomes — by end of Day 3, students can…

Explain terminal vs. shellDescribe the difference between a terminal emulator and bash, and why the distinction matters

Navigate between TTYsSwitch between GUI and text TTYs using keyboard shortcuts and explain what each is

Name filesystem hierarchy dirsState the purpose of /, /bin, /etc, /home, /var, /tmp, /opt, /dev, and /proc from memory

Write absolute and relative pathsGiven a current directory and a target, produce both the absolute and relative path correctly

Use mkdir, rmdir, cd, lsCreate and remove directories, navigate the filesystem, and interpret ls -l output

Handle filenames with spacesCreate and reference files and directories whose names contain spaces using quotes or escaping

What to have ready before class

Lab 2 handout printed (Parts 1–2 today, Parts 3–5 tomorrow) Filesystem hierarchy table on whiteboard or projector Both student VMs confirmed working at start of class

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