Capstone labs · Lesson 3 of 18 · 8 minutes

Capstone service map

Map service status, units, and listeners.

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Your objectives

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1
List 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.
2
Show sockets
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.
3
Show open sockets
Run lsof -i.
Hint & worked example
Inspect a synthetic association between processes and open files or sockets.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
lsof -i
```
Remember: Combine process and socket evidence rather than assuming a service from its port number.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

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.
ss: Inspect simulated listening sockets and connection information.
A listening socket is not proof of correct application responses or external reachability.
lsof: Inspect a synthetic association between processes and open files or sockets.
Combine process and socket evidence rather than assuming a service from its port number.

Worked example and expected result

$ 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.

$ 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.

$ lsof -i

COMMAND PID USER   FD  TYPE NAME
nginx    42 www    6u  IPv4 *:80 (LISTEN)
nginx    42 www    7u  IPv4 *:443 (LISTEN)
sshd     77 root   3u  IPv4 *:22 (LISTEN)

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 “Capstone service map”, which interpretation is safe?A listening socket is not proof of correct application responses or external reachability.A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.

Apply it elsewhere

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

Keep the momentum.

Complete the lab, then explain and apply the pattern.

Next: Capstone web config Try an incident drill

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