Phase 5 — Student Handouts

Sessions 65 + 68 · Week 17 · Handout R

Networking — commands, concepts, and exercises

Name

Date

Interface and addresses

ip addr showall interfaces + IPs

hostname -Imachine's IP addresses

ip route showrouting table, gateway

ss -tulpnlistening ports + services

Testing and diagnostics

ping -c 4 hosttest reachability

traceroute hosttrace route to host

dig hostnameDNS lookup details

nslookup hostsimple DNS resolution

curl

curl urlfetch and print

curl -o file urlsave to file

curl -I urlheaders only

curl -L urlfollow redirects

curl -X POST -d dataPOST request

DNS configuration files

/etc/hostslocal DNS overrides

/etc/resolv.confDNS server addresses

cat /etc/hostsread current overrides

Exercises — fill in commands and answers

1.What is your machine's local IP address? Which interface carries it?

Command

IP address

Interface name

2.What is the default gateway? What does that device do?

Command

Gateway IP

Its role

3.Run curl https://api.ipify.org — what IP does it return? How does it differ from your local IP?

Returned IP

Why different

What is NAT?

4.Use ss -tulpn. List 3 services listening on your machine — port, protocol, service name.

Port	Protocol	Service	What it does

5.Add an entry to /etc/hosts mapping "mycomputer" to 127.0.0.1. Test it with ping. Write the entry you added.

hosts entry

ping result

Sessions 66 + 67 · Week 17 · Handout S

SSH — connection and key authentication setup

Name

Date

Work through these steps in sequence. Each step builds on the last. Record every command you run and the key results. Partner A = server, Partner B = client — then swap.

Step 1Install and start SSH server (server machine)

Install: sudo apt install openssh-server

Enable and start: sudo systemctl enable --now ssh

Verify running: systemctl status ssh — shows "active (running)"

Find IP: ip addr show

Server IP: Username:

Step 2Connect with password (client machine)

Connect: ssh username@server_ip

Accept host key fingerprint (type "yes")

Run hostname — does it show the server's hostname?

Run who — can you see your session listed?

who output shows:

Disconnect: exit or Ctrl+D

Step 3Generate SSH key pair (client machine)

Generate: ssh-keygen -t ed25519 -C "yourname-course"

Accept default path (~/.ssh/id_ed25519)

Set a passphrase (recommended) or press Enter for none

View public key: cat ~/.ssh/id_ed25519.pub

Public key starts with:

Step 4Copy public key to server

Copy: ssh-copy-id username@server_ip

SSH again — are you prompted for a password? (Should not be)

Check permissions: ls -la ~/.ssh/

File	Required permissions	Actual permissions
~/.ssh/	700
id_ed25519	600
id_ed25519.pub	644

Test: set private key to 644, try SSH — read the error. Set it back to 600.

Step 5SSH config shortcut

Create or edit ~/.ssh/config with nano

Host partner
    HostName server_ip
    User username
    IdentityFile ~/.ssh/id_ed25519

Test: ssh partner — does it connect?

Transfer a file: scp ~/scripts/greet.sh partner:/tmp/

Key concepts — answer without notes

Why is SSH key authentication more secure than password authentication?

What is the difference between the public key and the private key? What happens if someone gets your private key?

Session 72 · Week 19 · Handout T

Debugging — diagnosing and fixing broken systems

Name

Date

For each scenario: describe the problem precisely, list every diagnostic command you run (with output), identify the root cause (not the symptom), apply the fix, and verify it worked.

Debugging method: (1) describe precisely, (2) reproduce reliably, (3) gather information, (4) hypothesise, (5) test one change, (6) find root cause not symptom

Scenario 1 — broken service

A service unit file has a syntax error. systemctl start fails.

Precise problem description

Diagnostic commands run

Root cause (specific, not "syntax error")

Fix applied + verification command

Scenario 2 — permission denied

A script exists. The path is correct. Running it gives "permission denied."

Diagnostic commands run

What ls -l shows about the file

Root cause

Fix + verification

Scenario 3 — missing command

A script calls a command that is not installed. "Command not found."

Command that was missing

How you found the package name

Install command

Verification

Scenario 4 — SSH service config error

SSH will not start after editing sshd_config. Use the built-in config tester.

Built-in config test command

Error output (exact)

Line with error + what was wrong

Fix + verification

Reflection

What is the difference between a symptom and a root cause? Give one example from today's scenarios.

Sessions 74 + 75 · Week 20 · Handout U

Cron and git — reference and exercises

Name

Date

Cron syntax

MIN HOUR DOM MON DOW command
 *    *    *   *   *  every minute
 0    3    *   *   *  3am daily
 0    3    *   *   0  3am every Sunday
*/5   *    *   *   *  every 5 minutes
 0   9-17  *   *  1-5 9am-5pm weekdays

crontab -eedit your crontab

crontab -llist current crontab

crontab -rremove all (careful)

Always use absolute paths. Always redirect: >> /log 2>&1

Core git workflow

git initcreate repository

git statuswhat changed

git add .stage all changes

git commit -m "msg"save snapshot

git log --onelinecompact history

git diffunstaged changes

git checkout -- fileundo file changes

git show HASHview a commit

Cron exercises

1.Write a crontab entry to run your backup script at 2:30am every day.

Entry

2.Decode these cron entries — when does each run?

0 0 1 * *

*/10 * * * 1-5

30 8 * * 1

3.Why must cron jobs use absolute paths? Give a real example of what breaks without them.

Git exercises

4.Initialise a git repo in ~/dotfiles. Add and commit your .bashrc. Show the log entry.

Commands

git log shows

5.Accidentally delete 2 lines from .bashrc. Use git to recover the file. Show the command.

Recovery command

Why this works

6.What are the three areas in git? What command moves changes from area 1 to area 2? From area 2 to area 3?

Area 1

→

Area 2

→

Area 3

Session 80 · Week 20 · Handout V

Phase 5 vocabulary checklist

Name

Date

Tick the green box if you can explain the term clearly. Tick the red box if you need to review it.

I can explain this

I need to review

Week 16 — bash scripting depth

case statement

bash array

string manipulation ${}

$(( arithmetic ))

getopts / OPTARG

heredoc (EOF)

set -euo pipefail

trap EXIT / ERR

lockfile pattern

Week 17 — networking and SSH

IP address / IPv4

private IP / NAT

port number

DNS / TTL

ip addr / ip route

ping / traceroute

ss -tulpn

SSH / port 22

host key fingerprint

scp

public key / private key

authorized_keys

ssh-keygen -t ed25519

~/.ssh/config

curl / wget

Week 18 — processes and services

process / PID

process state (R/S/D/Z)

ps aux / htop

SIGTERM / SIGKILL

background (&)

systemd / PID 1

unit file

systemctl

journalctl -u

Weeks 19–20 — logs, archives, cron, git, disk

/var/log/syslog

/var/log/auth.log

journalctl -p err

root cause vs symptom

tar -czf / -xzf

gzip / zip

crontab -e / -l

cron time syntax

cron minimal environment

git init / add / commit

git log / diff / show

git branch / merge

df -h / du -sh

apt clean / autoremove

sudoers / visudo

Phase 5 reflection

1. What is the single most useful skill you learned in Phase 5? Why?

2. Describe your health-check script: what it monitors, one interesting implementation, one problem you debugged.

3. What do you plan to build for the Phase 6 final project? Why?