Server operations · Lesson 28 of 36 · 8 minutes

Open file triage

Map open sockets and processes to services.

Open the lab Course map

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learner@clairos:~ $

↑ history · Tab complete · Ctrl+C cancel · Esc, Tab to leaveExit 0

Your objectives

Hints are always available. Wrong turns never cost XP.

1
Show 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.
2
Find nginx pid
Run pgrep nginx.
Hint & worked example
Find simulated process IDs by a name pattern.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
pgrep nginx
```
Remember: Verify a process identity before sending a signal.
3
Check nginx
Run systemctl status nginx.
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 status nginx
```
Remember: A service can be active while an application endpoint is unhealthy; verify both layers.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

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.
pgrep: Find simulated process IDs by a name pattern.
Verify a process identity before sending a signal.
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

$ 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.

$ pgrep nginx

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

$ systemctl status nginx

nginx.service - simulated nginx
   Loaded: loaded
   Active: active
   Notes: serving the simulated static learn site

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 “Open file triage”, which interpretation is safe?A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.Verify a process identity before sending a signal.

Apply it elsewhere

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

Keep the momentum.

Complete the lab, then explain and apply the pattern.

Next: Backup service note Try an incident drill

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