Week 4 Overview — NETW-0001 Operating Systems Fundamentals

Week OverviewMon – Fri · 10 hours total

Redirects, pipes, text editors, compression, and cron — the vocabulary of Linux administration

Week 4 is deliberately placed before scripting because these tools are the vocabulary that makes scripting possible. A student who can't confidently redirect output to a file, pipe commands together, or edit a config file in nano will struggle to write meaningful Bash scripts in Week 5. By Friday every student can chain commands, schedule tasks with cron, compress archives three different ways, and edit files without leaving the terminal.

Week at a glance

Monday

Redirects & Pipes

>, >>, 2>, |, tee, xargs — chaining commands and capturing output

Tuesday

Text Editors & Environment

nano fluency, vim basics, $PATH, export, .bashrc, environment variables

Wednesday

Compression & Archives

tar, gzip, bzip2, lzma — create, list, extract, append, compare sizes

Thursday

Cron & Scheduling

crontab syntax, user and system crontabs, verify with syslog

Friday

Mini-Assessment 4

Written: cron syntax, compression theory. Practical: pipe/redirect challenge + cron job.

⭐ OverTheWire BanditStanding challenge — not assessed

Week 4 target: Levels 11–14

Level 11 uses tr for character rotation (ROT13). Level 12 involves a hex dump that must be decompressed multiple times using gzip, bzip2, and tar — a perfect match for Wednesday's compression lab. Level 13 introduces SSH private key authentication, which previews Week 6. Level 14 uses netcat for network communication.

Learning OutcomesBy end of Week 4, students can…

Use I/O redirectionRedirect stdout and stderr to files, append output, and discard error messages

Chain commands with pipesBuild multi-command pipelines; use tee to split output to file and screen

Edit files in the terminalNavigate and save files in nano; perform basic operations in vim (open, edit, save, quit)

Manage environment variablesInspect $PATH, export variables, modify .bashrc persistently

Create and extract archivesUse tar with gzip, bzip2, and lzma compression; compare sizes and explain trade-offs

Write and schedule cron jobsWrite correct crontab syntax, schedule tasks for student and root, verify execution

MondayLecture + guided lab · 2 hrs

I/O redirection and pipes — the glue that holds Linux together

0:00–0:10
Recap

0:10–0:40
Lecture

0:40–1:50
Guided lab

1:50–2:00
Debrief

Lecture (30 min): Every command has stdin (0), stdout (1), and stderr (2). Normally these connect to the terminal. Redirection changes that. > sends stdout to a file (overwrites). >> appends. 2> redirects errors. 2>&1 merges stderr into stdout. /dev/null — the black hole. Pipes (|) connect stdout of one command to stdin of the next — no temp files needed. tee splits: sends to file AND stdout simultaneously. xargs converts stdin into arguments for another command. Bridge: Windows PowerShell has pipes too (|) — same concept, but Linux pipes are older and more fundamental to the OS design.
Guided lab (70 min): Redirect ls -l /etc to a file. Append the date to the same file. Redirect errors from a permission-denied command to a separate error log. Build pipelines: ls /etc | grep conf | wc -l. Use tee to log output while still seeing it on screen. Use xargs to delete a list of files. Challenge: use a pipeline to find the five largest files in /var/log, sorted by size.

The pipeline mindset: Emphasise that Linux tools are designed to do one thing well and work together. grep doesn't need a sort feature — it pipes to sort. sort doesn't need a deduplicate feature — it pipes to uniq. This Unix philosophy is why pipes matter.

TuesdayLecture + guided lab · 2 hrs

Text editors and environment — nano, vim basics, PATH, and .bashrc

0:00–0:10
Recap

0:10–0:35
Lecture

0:35–1:50
Guided lab

1:50–2:00
Debrief

Lecture (25 min): Terminal text editors are essential — SSH sessions have no GUI. nano: beginner-friendly, keyboard shortcuts shown at the bottom. Open, navigate, edit, save (Ctrl+O), exit (Ctrl+X), search (Ctrl+W), cut line (Ctrl+K), paste (Ctrl+U). vim: modal editor — Normal mode for navigation, Insert mode (i) for typing, Command mode (:) for saving/quitting. Minimum survival kit: i to insert, Esc to normal, :w to write, :q! to quit without saving. Environment variables: $HOME, $USER, $PATH, $SHELL. echo $PATH — the colon-separated list of directories searched for commands. export VAR=value — make a variable available to child processes. .bashrc and .bash_profile — where persistent customisations live. which command — find where a command lives in PATH.
Guided lab (75 min): Edit /etc/hosts safely in nano — add a custom hostname entry, save, verify with ping. Open a file in vim, navigate, make a change, save, and quit. Inspect $PATH — identify which directories it contains. Add a custom directory to PATH in .bashrc and source it. Create a simple alias in .bashrc (alias ll='ls -la'). Verify it persists after opening a new terminal.

Common student trap: Students often get stuck in vim and can't exit. Demonstrate :q! before they start. "If you're ever stuck in vim, Esc Esc :q! Enter always gets you out."

WednesdayLecture + Lab 6 Part 1 · 2 hrs

Compression and archives — tar, gzip, bzip2, lzma

0:00–0:10
Recap

0:10–0:35
Lecture

0:35–1:50
Lab 6 Pt 1

1:50–2:00
Debrief

Lecture (25 min): Windows uses .zip by default; Linux has multiple formats. tar (tape archive) collects files into one archive — no compression by default. Compression is layered on top: -z for gzip (.tar.gz), -j for bzip2 (.tar.bz2), -J for lzma/xz (.tar.xz). Key tar switches: -c create, -x extract, -t list, -f file, -v verbose, -r append (uncompressed only), --delete remove from archive. Relative vs. absolute paths in archives — leading / stripped by default for safety. Compression comparison: gzip is fastest, bzip2 better compression, lzma/xz best compression but slowest.
Lab 6 Part 1 (75 min): Create test files with specific content. Build foo.tar from three files. List the archive. Create foo2.tar from a fourth file. Append foo2.tar contents to foo.tar. Delete a file from the archive. Extract a single file, edit it, put it back. Create three tarballs of /usr/src/* using gzip, bzip2, and lzma — compare resulting sizes and determine which compresses best for that data.

Lab highlight: The movie quote in file4 ("Ministers, more sinister than ministers!") is from The Rocky Horror Picture Show — the lab notes say the instructor will be impressed if a student gets it. Keep it in. It makes lab marking memorable.

ThursdayLecture + Lab 6 Part 2 · 2 hrs

Cron — scheduling automated tasks

0:00–0:10
Recap

0:10–0:35
Lecture

0:35–1:45
Lab 6 Pt 2

1:45–1:55
Bonus

1:55–2:00
Wrap

Lecture (25 min): Cron runs commands on a schedule — like Windows Task Scheduler. crontab -e edits the current user's cron jobs. crontab -l lists them. crontab -r removes all (dangerous — warn students). Cron syntax: five fields — minute (0–59), hour (0–23), day of month (1–31), month (1–12), day of week (0–6, 0=Sunday). Special values: * any, */5 every 5, 1,15 first and fifteenth. System-wide crontabs live in /etc/crontab and /etc/cron.d/ — these have an extra user field. Cron output goes to the user's mail by default; redirect to a file with >> and 2>&1. Verify execution with grep CRON /var/log/syslog.
Lab 6 Part 2 (70 min): Check existing cron jobs for student, root, and system-wide. Create cron jobs: run a script every minute (for testing), run a backup script every day at 2am, run a cleanup every first of the month. Verify execution by watching syslog. Create a root cron job using sudo crontab -e. Answer: what command shows current time in terminal? (date)
Bonus (10 min): anacron vs. cron — what happens to missed jobs when the system was off? Introduce /etc/cron.daily, /etc/cron.weekly drop-in directories.

FridayMini-Assessment 4 · 2 hrs

Mini-Assessment 4 — CLI Power Tools

0:00–0:25
Written

0:25–1:50
Practical

1:50–2:00
Review

Written (25 min, 30%): Given a cron line, state exactly when it runs. Convert a cron schedule description to cron syntax. Explain the difference between > and >>. Name the three compression formats covered this week and state one advantage of each. Explain what $PATH is and what happens when a command is not found.
Practical (85 min, 70%): Pipeline challenge — given a series of tasks (find files meeting criteria, count unique occurrences, format output to a file), students build pipelines using the tools from Monday. Compression task — archive a specified directory with each compression method and report sizes. Cron task — write two cron jobs to a specification and demonstrate they run correctly using syslog.

Topic	Weight	Format
Cron syntax reading and writing	15%	Written + Practical
Redirection operators (>, >>, 2>, 2>&1)	10%	Written
Compression formats and trade-offs	5%	Written
Pipeline construction challenge	30%	Practical
Compression/archive tasks	20%	Practical
Cron job creation and verification	20%	Practical

What you need ready before Monday

Lab 6 handout printed Mini-Assessment 4 printed (Friday) /usr/src/ populated on student VMs for compression lab

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