Text and logs · Lesson 36 of 38 · 8 minutes

Rotated access comparison

Compare active and rotated access logs before summarizing traffic.

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learner@clairos:~ $

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Your objectives

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1
Compare active and rotated logs
Run diff /var/log/nginx-access.log /var/log/nginx-access.log.1.
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 /var/log/nginx-access.log /var/log/nginx-access.log.1
```
Remember: Status 1 means differences for diff; shell status must be interpreted in command context.
2
Read recent rotated entries
Run tail -n 2 /var/log/nginx-access.log.1.
Hint & worked example
Show the end of an input; -n selects the number of lines.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
tail -n 2 /var/log/nginx-access.log.1
```
Remember: This browser lab snapshots output; it does not keep a live tail -f stream.
3
Number the active log
Run nl /var/log/nginx-access.log.
Hint & worked example
Number input lines for a readable evidence reference.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
nl /var/log/nginx-access.log
```
Remember: Line numbers depend on the exact file version and numbering mode.

Understand the pattern

Comparing current and rotated log evidence helps operators explain what they know before they change anything.

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.
tail: Show the end of an input; -n selects the number of lines.
This browser lab snapshots output; it does not keep a live tail -f stream.
nl: Number input lines for a readable evidence reference.
Line numbers depend on the exact file version and numbering mode.

Worked example and expected result

$ diff /var/log/nginx-access.log /var/log/nginx-access.log.1

--- /var/log/nginx-access.log
+++ /var/log/nginx-access.log.1
-127.0.0.1 GET / 200
+127.0.0.1 GET /unix/ 200
-127.0.0.1 GET /assets/learn-terminal.js 200
+127.0.0.1 GET /unix/courses/ 200
-127.0.0.1 GET /api/test 404
+127.0.0.1 GET /missing 404
-127.0.0.1 POST / 405
+

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

$ tail -n 2 /var/log/nginx-access.log.1

127.0.0.1 GET /unix/courses/ 200
127.0.0.1 GET /missing 404

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

$ nl /var/log/nginx-access.log

     1	127.0.0.1 GET / 200
     2	127.0.0.1 GET /assets/learn-terminal.js 200
     3	127.0.0.1 GET /api/test 404
     4	127.0.0.1 POST / 405

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 “Rotated access comparison”, which interpretation is safe?A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.This browser lab snapshots output; it does not keep a live tail -f stream.

Apply it elsewhere

Before adapting the tail workflow from “Rotated access comparison” 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 template numbering Try an incident drill

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