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World L3: Phone Lines · Boss challenge

Why can't the customer reach the shop?

You will learn: to climb the can't-connect ladder on your own and fix four rungs.

Checked with Linux (Debian 13) on 1 Nov 2026

The problem

Boss! Customers phone in: “menu.kedai won’t open!” You log in to kedai. Which rung do you check first?

Try it

Rung 1, the name. Ask getent hosts menu.kedai, read /etc/hosts, then fix it. kedai’s own number is 10.0.0.5.

You are hereyou@kedai:~$

Folder ~

Empty folder

+ 3 hidden (ls -a)

Services

  • cronrunningstarts at boot
  • sshrunningstarts at boot
  • nginxrunningstarts at boot

Phone lines (network) Address 10.0.0.5

Listening ports

  • :22 sshd
  • :80 nginx

Watch

Rung 2, the door number. curl localhost is refused at once. Here is ss -tln. Tap where nginx answers now.

Tap the line for the web counter.

0 of 1 found

Try it

Move nginx back to port 80. Change the listen line, test with sudo nginx -t, then restart nginx.

You are hereyou@kedai:~$

Folder ~

Empty folder

+ 3 hidden (ls -a)

Services

  • cronrunningstarts at boot
  • sshrunningstarts at boot
  • nginxrunningstarts at boot

Phone lines (network) Address 10.0.0.5

Listening ports

  • :22 sshd
  • :8080 nginx

Watch

kedai
sudo ufw status
Status: active
To Action From
-- ------ ----
OpenSSH ALLOW Anywhere

Rung 3. From a laptop outside, curl says Connection timed out after 5004 milliseconds. Plain words: a guard drops the call. Port 80 is not on the guard’s list.

Try it

Build the command that lets web customers in, and keeps the guard on duty.

Tap the pieces in the right order.

…

Try it

Rung 4. Last night kedai rebooted, and nginx stayed off. Start it now, and make it start at every boot.

You are hereyou@kedai:~$

Folder ~

Empty folder

+ 3 hidden (ls -a)

Services

  • cronrunningstarts at boot
  • sshrunningstarts at boot
  • nginxstoppedoff at boot

Phone lines (network) Address 10.0.0.5

Listening ports

  • :22 sshd

Check

Write the night’s report. Put the fixes in ladder order.

First fix at the top. Put these in order. Use the arrows, or drag.

  • Allowed 80/tcp in ufw
  • Enabled and started nginx
  • Moved nginx back to port 80
  • Added menu.kedai to /etc/hosts

You did it!

You can now find and fix why customers can’t reach a server, rung by rung.

Go deeper (optional)

Your ladder card: getent hosts (name), ping (road), curl -v --connect-timeout 5 (door), sudo ss -tlnp and systemctl status (staff), the status code and journalctl (answer).

Real mission

  2. sudo systemctl stop nginx
  3. curl -sv --connect-timeout 5 http://YOUR-VM-IP
  4. sudo systemctl start nginx

0 of 4 steps done · Your ticks are saved.