Text and logs · Lesson 31 of 38 · 8 minutes

Numbered log reading

Add stable line numbers to a short authentication-log view.

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learner@clairos:~ $

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Your objectives

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1
Number the auth log
Run nl /var/log/auth.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/auth.log
```
Remember: Line numbers depend on the exact file version and numbering mode.
2
Read the first numbered lines
Run nl /var/log/auth.log | head -n 3.
Hint & worked example
Number input lines for a readable evidence reference. Show the beginning of an input; -n sets how many lines to include.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
nl /var/log/auth.log | head -n 3
```
Remember: Line numbers depend on the exact file version and numbering mode. A small sample may omit the failure. Choose the time window you actually need.
3
Count the source lines
Run wc -l /var/log/auth.log.
Hint & worked example
Count input. -l counts newline characters, -w counts whitespace-delimited words, and -c counts bytes.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
wc -l /var/log/auth.log
```
Remember: Text without a final newline may have fewer counted lines than visible rows.

Understand the pattern

Citing exact lines from log evidence helps operators explain what they know before they change anything.

nl: Number input lines for a readable evidence reference.
Line numbers depend on the exact file version and numbering mode.
head: Show the beginning of an input; -n sets how many lines to include.
A small sample may omit the failure. Choose the time window you actually need.
wc: Count input. -l counts newline characters, -w counts whitespace-delimited words, and -c counts bytes.
Text without a final newline may have fewer counted lines than visible rows.

Worked example and expected result

$ nl /var/log/auth.log

     1	May 26 08:14:02 clairos-learn sshd[104]: accepted publickey for learner
     2	May 26 08:18:33 clairos-learn sshd[118]: denied password for root
     3	May 26 08:19:10 clairos-learn sudo[126]: learner : command=list services
     4	May 26 08:21:44 clairos-learn sshd[141]: denied password for admin

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

$ nl /var/log/auth.log | head -n 3

     1	May 26 08:14:02 clairos-learn sshd[104]: accepted publickey for learner
     2	May 26 08:18:33 clairos-learn sshd[118]: denied password for root
     3	May 26 08:19:10 clairos-learn sudo[126]: learner : command=list services

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

$ wc -l /var/log/auth.log

3 /var/log/auth.log

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 “Numbered log reading”, which interpretation is safe?Line numbers depend on the exact file version and numbering mode.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 nl workflow from “Numbered log reading” 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.

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