Security administration · Lesson 12 of 35 · 7 minutes

Log retention review

Review log size and line counts before cleanup decisions.

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Your objectives

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1
Size logs
Run du -sh /var/log.
Hint & worked example
Estimate usage attributed to files or directories; compare it with filesystem capacity when investigating storage.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
du -sh /var/log
```
Remember: du describes file usage, whereas df describes filesystem capacity.
2
Find logs
Run find /var/log -name log.
Hint & worked example
Search directory trees by criteria rather than relying on one shallow listing.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
find /var/log -name log
```
Remember: Quote wildcard patterns so find receives them instead of the shell expanding them first.
3
Count auth log
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

Retention decisions should be evidence-aware.

du: Estimate usage attributed to files or directories; compare it with filesystem capacity when investigating storage.
du describes file usage, whereas df describes filesystem capacity.
find: Search directory trees by criteria rather than relying on one shallow listing.
Quote wildcard patterns so find receives them instead of the shell expanding them first.
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

$ du -sh /var/log

3K	/var/log

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

$ find /var/log -name log

/var/log
/var/log/auth.log
/var/log/cron.log
/var/log/dpkg.log
/var/log/journal/backup.log
/var/log/journal/nginx.log
/var/log/journal/ssh.log
/var/log/kern.log
/var/log/nginx-access.log
/var/log/nginx-access.log.1
/var/log/nginx-error.log
/var/log/nginx-error.log.1
/var/log/syslog

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 “Log retention review”, which interpretation is safe?A successful first check guarantees that every dependent service is healthy.Quote wildcard patterns so find receives them instead of the shell expanding them first.A command appearing in history proves it completed successfully.

Apply it elsewhere

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

Keep the momentum.

Complete the lab, then explain and apply the pattern.

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