Scheduled data collection with cron in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to schedule a script to run every minute using cron syntax.

Raspberry Pi

* * * * [1] /home/pi/data_collect.sh

Drag options to blanks, or click blank then click option'

A*

B1

C0

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number instead of * causes the job to run only on that specific day.

The asterisk (*) means 'every' in cron syntax. Here, the last asterisk means every day of the week.

2fill in blank

medium

Complete the cron schedule to run a script every hour at minute 30.

Raspberry Pi

30 [1] * * * /home/pi/data_collect.sh

Drag options to blanks, or click blank then click option'

A0

B1

C*

D30

Attempts:

3 left

💡 Hint

Common Mistakes

Putting 30 in the hour field causes the script to run only at 30:00 which is invalid.

The asterisk (*) in the hour field means every hour. So the script runs at minute 30 of every hour.

3fill in blank

hard

Fix the error in the cron command to run a script every day at 6 AM.

Raspberry Pi

[1] 6 * * * /home/pi/data_collect.sh

Drag options to blanks, or click blank then click option'

A6

B30

C*

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting minutes to 6 causes the script to run at 6 minutes past every hour.

The first field is minutes. To run at 6:00 AM, minutes should be 0 and hour 6.

4fill in blank

hard

Fill both blanks to schedule a script to run every Monday at 7 AM.

Raspberry Pi

0 [1] * * [2] /home/pi/data_collect.sh

Drag options to blanks, or click blank then click option'

A7

B1

C0

D6

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 for day of week runs on Sunday, not Monday.

The hour is 7 for 7 AM, and 1 in the day-of-week field means Monday.

5fill in blank

hard

Fill all three blanks to schedule a script to run at 5:15 PM on the 10th day of every month.

Raspberry Pi

[1] [2] [3] * * /home/pi/data_collect.sh

Drag options to blanks, or click blank then click option'

A15

B17

C10

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 5 for hour runs at 5 AM, not 5 PM.

Minute is 15, hour is 17 (5 PM in 24-hour format), and day of month is 10.

Practice

1. What is the main purpose of using cron on a Raspberry Pi for database tasks?

easy

A. To create database backups only when the Pi is restarted

B. To manually start database queries

C. To store data permanently

D. To automatically run scripts at scheduled times

Solution

1. Step 1: Understand cron's role

   Cron is a tool that runs commands or scripts automatically at set times without user intervention.

2. Step 2: Connect cron to database tasks

   Using cron, you can schedule database scripts to run regularly, like collecting data or backups.

3. Final Answer:

   To automatically run scripts at scheduled times -> Option D

4. Quick Check:

   Cron automates tasks = A [OK]

Hint: Cron schedules tasks automatically, no manual start needed [OK]

Common Mistakes:

• Thinking cron runs scripts only manually
• Confusing cron with data storage
• Assuming cron runs only at reboot

2. Which of the following is the correct command to edit the cron jobs on a Raspberry Pi?

easy

A. crontab -e

B. cronedit

C. cron -edit

D. editcron

Solution

1. Step 1: Recall the standard cron command

   The command to edit cron jobs is crontab -e, which opens the cron table for editing.

2. Step 2: Verify other options

   Other options like cronedit, cron -edit, and editcron are not valid commands.

3. Final Answer:

   crontab -e -> Option A

4. Quick Check:

   Edit cron jobs = crontab -e [OK]

Hint: Use 'crontab -e' to edit cron jobs every time [OK]

Common Mistakes:

• Typing 'cronedit' instead of 'crontab -e'
• Using wrong command syntax
• Confusing cron commands with other tools

3. Given this cron job entry:
0 * * * * /home/pi/scripts/collect_data.sh
What does this cron job do?

medium

A. Runs the script every minute

B. Runs the script every hour at minute 0

C. Runs the script once a day at midnight

D. Runs the script every day at noon

Solution

1. Step 1: Understand cron time format

   The five fields represent minute, hour, day of month, month, and day of week. '0 * * * *' means minute 0 of every hour.

2. Step 2: Interpret the schedule

   This means the script runs at the start of every hour (e.g., 1:00, 2:00, 3:00, etc.).

3. Final Answer:

   Runs the script every hour at minute 0 -> Option B

4. Quick Check:

   Minute 0 every hour = hourly run [OK]

Hint: Minute 0 with * hour means hourly at start [OK]

Common Mistakes:

• Thinking it runs every minute
• Confusing hour and minute fields
• Assuming daily or noon run

4. A user added this cron job:
*/15 * * * * collect_data.sh
But the script does not run. What is the most likely problem?

medium

A. The script path is missing; cron needs full path

B. The cron syntax is invalid

C. The script runs only once a day

D. Cron does not support scripts with .sh extension

Solution

1. Step 1: Check cron job command

   The command collect_data.sh lacks a full path. Cron requires full paths to scripts.

2. Step 2: Understand cron environment

   Cron runs with a minimal environment and does not know where to find scripts without full paths.

3. Final Answer:

   The script path is missing; cron needs full path -> Option A

4. Quick Check:

   Always use full script path in cron [OK]

Hint: Always specify full script path in cron jobs [OK]

Common Mistakes:

• Assuming cron finds scripts in current directory
• Thinking .sh extension is unsupported
• Believing syntax is wrong when it is correct

5. You want to collect sensor data every day at 6:30 AM and save it to a database using a script at /home/pi/scripts/save_data.sh. Which cron entry correctly schedules this?

hard

A. 30 06 * * 1-5 /home/pi/scripts/save_data.sh

B. 6 30 * * * /home/pi/scripts/save_data.sh

C. 30 6 * * * /home/pi/scripts/save_data.sh

D. 0 6 * * * /home/pi/scripts/save_data.sh

Solution

1. Step 1: Understand cron time fields

   The format is: minute hour day month weekday. To run at 6:30 AM daily, minute=30 and hour=6.

2. Step 2: Check each option

   30 6 * * * /home/pi/scripts/save_data.sh uses '30 6 * * *' which means 6:30 AM every day. 6 30 * * * /home/pi/scripts/save_data.sh reverses minute and hour. 30 06 * * 1-5 /home/pi/scripts/save_data.sh restricts to weekdays only. 0 6 * * * /home/pi/scripts/save_data.sh runs at 6:00 AM.

3. Final Answer:

   30 6 * * * /home/pi/scripts/save_data.sh -> Option C

4. Quick Check:

   Minute 30, hour 6 daily = 30 6 * * * /home/pi/scripts/save_data.sh [OK]

Hint: Minute first, then hour in cron time fields [OK]

Common Mistakes:

• Swapping hour and minute fields
• Forgetting to specify full script path
• Limiting days unintentionally