Scheduled data collection with cron in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this cron schedule?

Given the cron expression 30 2 * * 1-5, when will the scheduled task run?

A At 2:30 AM every weekday (Monday to Friday)

B At 2:30 PM every day

C At 2:00 AM every Monday to Friday

D At 30 minutes past every hour on weekdays

💡 Hint

Remember the order of fields in a cron expression: minute, hour, day of month, month, day of week.

The cron expression means: minute 30, hour 2, every day of month, every month, days Monday to Friday (1-5). So it runs at 2:30 AM on weekdays.

📝 Syntax

intermediate

Identify the syntax error in this cron job entry

Which option shows a syntax error in a cron job entry?

A 0 25 * * * /home/pi/script.sh

B 0 0 * * 0 /home/pi/script.sh

C 15 14 1 * * /home/pi/script.sh

D */10 * * * * /home/pi/script.sh

💡 Hint

Check the valid range for the hour field in cron.

The hour field must be between 0 and 23. '25' is invalid and causes a syntax error.

❓ optimization

advanced

Optimize this cron schedule for hourly data collection

You want to collect data every hour at 15 minutes past the hour. Which cron expression is the most efficient and correct?

A */15 * * * * /home/pi/collect_data.sh

B 0 15 * * * /home/pi/collect_data.sh

C 15 * * * * /home/pi/collect_data.sh

D 15 0-23 * * * /home/pi/collect_data.sh

💡 Hint

Remember the order: minute, hour, day, month, weekday.

Option C runs the script at minute 15 of every hour, every day, which matches the requirement.

🔧 Debug

advanced

Why does this cron job not run as expected?

A cron job entry is: 0 6 * * * /home/pi/data_collect.sh. The script runs fine manually but does not run at 6 AM. What is the most likely cause?

A The script path is incorrect because cron uses a different working directory

B Cron does not support running scripts at 6 AM

C The cron daemon is not installed on Raspberry Pi

D The script lacks execute permissions for the user running cron

💡 Hint

Check permissions and environment differences between manual and cron runs.

If the script is not executable by the cron user, it won't run even if scheduled correctly.

🧠 Conceptual

expert

How to ensure data collection runs even if the previous run is still active?

You schedule a data collection script every 10 minutes with cron. Sometimes the script takes longer than 10 minutes. Which approach ensures no overlapping runs?

A Run multiple instances in parallel to speed up data collection

B Use a lock file in the script to check if a previous instance is running and exit if so

C Restart the Raspberry Pi before each scheduled run

D Schedule the cron job every 5 minutes instead of 10

💡 Hint

Think about how to prevent multiple script instances from running simultaneously.

Using a lock file prevents overlapping runs by letting the script detect if another instance is active.