Security administration · Lesson 33 of 35 · 8 minutes

Exposed service inventory

Compare listeners, firewall policy, and enabled service units.

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Your objectives

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1
List network listeners
Run ss -tulpn.
Hint & worked example
Inspect simulated listening sockets and connection information.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
ss -tulpn
```
Remember: A listening socket is not proof of correct application responses or external reachability.
2
Read firewall policy
Run ufw status verbose.
Hint & worked example
Inspect or adjust the training firewall rule list. No real firewall changes occur.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
ufw status verbose
```
Remember: Firewall rules should be scoped and reviewed; simulator access is not a production change approval.
3
List service units
Run systemctl list-units.
Hint & worked example
Inspect or change a simulated systemd service. Status, active state, and unit configuration reveal different evidence.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
systemctl list-units
```
Remember: A service can be active while an application endpoint is unhealthy; verify both layers.

Understand the pattern

Reconciling exposed ports with intended services helps operators explain what they know before they change anything.

ss: Inspect simulated listening sockets and connection information.
A listening socket is not proof of correct application responses or external reachability.
ufw: Inspect or adjust the training firewall rule list. No real firewall changes occur.
Firewall rules should be scoped and reviewed; simulator access is not a production change approval.
systemctl: Inspect or change a simulated systemd service. Status, active state, and unit configuration reveal different evidence.
A service can be active while an application endpoint is unhealthy; verify both layers.

Worked example and expected result

$ ss -tulpn

Netid State  Local Address:Port  Process
udp   UNCONN 0.0.0.0:68          lab-dhcp
tcp   LISTEN 0.0.0.0:22          sshd
tcp   LISTEN 0.0.0.0:80          nginx
tcp   LISTEN 0.0.0.0:443         nginx

Exit status: 0. The command completed successfully in the training fixture.

$ ufw status verbose

Status: active
Logging: on (simulated)
Default: deny incoming, allow outgoing
- allow 22/tcp
- allow 80/tcp
- allow 443/tcp
- deny 23/tcp

Exit status: 0. The command completed successfully in the training fixture.

$ systemctl list-units

UNIT                  LOAD   ACTIVE
nginx.service loaded active simulated serving the simulated static learn site
ssh.service loaded active simulated accepting key-only training logins
cron.service loaded active simulated running scheduled simulated maintenance
backup.service loaded inactive simulated waiting for a configured backup target
database.service loaded inactive simulated not installed in this lab

Exit status: 0. The command completed successfully in the training fixture.

Try a variation

Repeat this workflow in the sandbox with a different scratch filename. Keep the system fixtures unchanged and compare the observed output with your expectation before moving on.

Explain it

In “Exposed service inventory”, which interpretation is safe?A successful first check guarantees that every dependent service is healthy.Firewall rules should be scoped and reviewed; simulator access is not a production change approval.A command appearing in history proves it completed successfully.

Apply it elsewhere

Before adapting the ufw workflow from “Exposed service inventory” to another server, what should you do?Confirm the current directory, target identity, permissions, and the installed command behavior first.Paste the training paths unchanged into production.Skip output inspection whenever the command is familiar.

Keep the momentum.

Complete the lab, then explain and apply the pattern.

Next: Privileged boundary review Try an incident drill

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