Troubleshooting · Lesson 20 of 26 · 8 minutes

Incident nginx config mismatch

Compare active config and expected config examples.

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learner@clairos:~ $

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

Your objectives

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1
Read active config
Run cat /etc/nginx/sites-available/learn.conf.
Hint & worked example
Read one or more files to standard output without editing their contents.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
cat /etc/nginx/sites-available/learn.conf
```
Remember: Reading a source file should precede changing it; avoid printing real secrets.
2
Compare examples
Run diff data/config-a.conf data/config-b.conf.
Hint & worked example
Compare two text files; a difference is a meaningful nonzero status, not necessarily an execution error.
Inspect the differences. diff exits 1 when files differ and 0 when they match.
```
diff data/config-a.conf data/config-b.conf
```
Remember: Status 1 means differences for diff; shell status must be interpreted in command context.
3
Find changed listen
Run grep listen data/config-b.conf.
Hint & worked example
Select input lines that match a pattern; -i ignores case, -n adds line numbers, and -v inverts selection.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
grep listen data/config-b.conf
```
Remember: No matches is exit status 1, which is different from a malformed invocation.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

cat: Read one or more files to standard output without editing their contents.
Reading a source file should precede changing it; avoid printing real secrets.
diff: Compare two text files; a difference is a meaningful nonzero status, not necessarily an execution error.
Status 1 means differences for diff; shell status must be interpreted in command context.
grep: Select input lines that match a pattern; -i ignores case, -n adds line numbers, and -v inverts selection.
No matches is exit status 1, which is different from a malformed invocation.

Worked example and expected result

$ cat /etc/nginx/sites-available/learn.conf

server {
  listen 443 ssl;
  server_name learn.clairos.ai;
  root /srv/www;
  location ^~ /api/learn/ { proxy_pass http://127.0.0.1:8010; }
  location ^~ /api/ { return 404; }
  add_header Content-Security-Policy "default-src 'self'; connect-src 'self'" always;
  # training config only
}

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

$ diff data/config-a.conf data/config-b.conf

--- /home/learner/data/config-a.conf
+++ /home/learner/data/config-b.conf
-listen 443 ssl;
+listen 8443 ssl;

Exit status: 1. This nonzero result is an expected part of this exercise.

$ grep listen data/config-b.conf

listen 8443 ssl;

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 “Incident nginx config mismatch”, which interpretation is safe?A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.Status 1 means differences for diff; shell status must be interpreted in command context.

Apply it elsewhere

Before adapting the diff workflow from “Incident nginx config mismatch” 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: Incident resource spike Try an incident drill

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