Troubleshooting · Lesson 18 of 26 · 8 minutes

Incident cron failure

Connect cron schedule, service, and logs.

Open the lab Course map

Mastery 0/3Run itExplain itApply it

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
List cron
Run crontab -l.
Hint & worked example
Inspect the simulated user schedule. No task is scheduled outside the browser.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
crontab -l
```
Remember: A scheduled entry is not proof that its last run succeeded.
2
Check cron service
Run systemctl status cron.
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 cron
```
Remember: A service can be active while an application endpoint is unhealthy; verify both layers.
3
Search cron log
Run grep CRON /var/log/cron.log.
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 CRON /var/log/cron.log
```
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.

crontab: Inspect the simulated user schedule. No task is scheduled outside the browser.
A scheduled entry is not proof that its last run succeeded.
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.
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

$ crontab -l

# learner training crontab
*/15 * * * * /home/learner/scripts/health-check.sh

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

$ systemctl status cron

cron.service - simulated cron
   Loaded: loaded
   Active: active
   Notes: running scheduled simulated maintenance

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

$ grep CRON /var/log/cron.log

May 26 08:00:00 clairos-learn CRON[126]: health-check.sh completed
May 26 08:15:00 clairos-learn CRON[126]: health-check.sh completed

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 cron failure”, which interpretation is safe?A successful first check guarantees that every dependent service is healthy.A service can be active while an application endpoint is unhealthy; verify both layers.A command appearing in history proves it completed successfully.

Apply it elsewhere

Before adapting the systemctl workflow from “Incident cron failure” 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.

Next: Incident backup inactive Try an incident drill

Anonymous lesson and mastery progress lasts for this session. Sign in to keep synced lesson XP between sessions; mastery stays device-local. No speed bonus, lost lives, or hint penalties.

Keep learning

GNU Coreutils manual · GNU Bash manual