Cron jobs for scheduled tasks in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to schedule a cron job that runs every minute.

Raspberry Pi

*/1 * * * * [1]

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

Arun script.py

B/usr/bin/python3 /home/pi/script.py

Cpython script.py

Dexecute script.py

Attempts:

3 left

💡 Hint

Common Mistakes

Using just 'python script.py' without full path causes cron to fail.

The cron job needs the full path to the Python interpreter and the script to run every minute.

2fill in blank

medium

Complete the cron schedule to run a job every day at 2:30 AM.

Raspberry Pi

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

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

A2

B14

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 14 instead of 2 runs at 2 PM, not 2 AM.

The hour field should be 2 for 2 AM in 24-hour format.

3fill in blank

hard

Fix the error in the cron job that should run every Sunday at midnight.

Raspberry Pi

0 0 * * [1] /home/pi/weekly_report.sh

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

A7

B0

CSun

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or 7 can be ambiguous depending on cron version.

Using 'Sun' is the correct way to specify Sunday in the day-of-week field for cron.

4fill in blank

hard

Fill both blanks to create a cron job that runs every 15 minutes and logs output.

Raspberry Pi

[1]/15 * * * * /home/pi/script.sh > [2] 2>&1

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

A*/

B/var/log/script.log

C/tmp/script.log

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' instead of '*/' causes the job to run every minute.

The '*/15' means every 15 minutes. Redirecting output to /tmp/script.log saves logs.

5fill in blank

hard

Fill all three blanks to create a cron job that runs at 5:45 PM on weekdays and emails output.

Raspberry Pi

[1] 45 17 [2] [3] /home/pi/daily_report.sh | mail -s "Report" [e-mail]

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

A1-5

B1,2,3,4,5

C1-7

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing day of month and day of week fields.

The minute field is '*', day of month is '1-5' for weekdays, and day of week is '1,2,3,4,5' for Monday to Friday.

Practice

1. What is the main purpose of a cron job on a Raspberry Pi?

easy

A. To update the Raspberry Pi operating system

B. To manually execute commands in the terminal

C. To schedule tasks to run automatically at specific times

D. To install new software packages

Solution

1. Step 1: Understand what cron jobs do

   Cron jobs are used to automate tasks by running commands or scripts at scheduled times without manual intervention.

2. Step 2: Compare options with cron job purpose

   Only To schedule tasks to run automatically at specific times describes scheduling tasks automatically, which matches the purpose of cron jobs.

3. Final Answer:

   To schedule tasks to run automatically at specific times -> Option C

4. Quick Check:

   Cron job purpose = schedule tasks automatically [OK]

Hint: Cron jobs run commands automatically on schedule [OK]

Common Mistakes:

• Confusing cron jobs with manual command execution
• Thinking cron updates the system automatically
• Assuming cron installs software

2. Which of the following is the correct syntax to edit the cron jobs for the current user on a Raspberry Pi?

easy

A. cronedit

B. cron -edit

C. editcron

D. crontab -e

Solution

1. Step 1: Recall the command to edit cron jobs

   The standard command to edit cron jobs for the current user is crontab -e.

2. Step 2: Verify other options

   Options A, B, and D are not valid Linux commands for editing cron jobs.

3. Final Answer:

   crontab -e -> Option D

4. Quick Check:

   Edit cron jobs command = crontab -e [OK]

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

Common Mistakes:

• Typing incorrect commands like 'cronedit'
• Using 'cron -edit' which is invalid
• Assuming 'editcron' is a command

3. Given the cron job entry 30 2 * * * /home/pi/backup.sh, what does it do?

medium

A. Runs backup.sh every day at 2:30 AM

B. Runs backup.sh every 30 minutes

C. Runs backup.sh every day at 2:00 PM

D. Runs backup.sh every 2 hours and 30 minutes

Solution

1. Step 1: Understand cron time fields

   The fields are: minute (30), hour (2), day of month (*), month (*), day of week (*). This means the command runs at 2:30 AM every day.

2. Step 2: Match the time to options

   Runs backup.sh every day at 2:30 AM correctly states it runs daily at 2:30 AM. Other options misunderstand the timing.

3. Final Answer:

   Runs backup.sh every day at 2:30 AM -> Option A

4. Quick Check:

   Cron time 30 2 * * * = 2:30 AM daily [OK]

Hint: Minute then hour in cron means 30 2 is 2:30 AM [OK]

Common Mistakes:

• Confusing AM and PM hours
• Thinking it runs every 30 minutes
• Misreading the asterisks as specific days

4. You added this cron job: 0 25 * * * /home/pi/script.sh but it never runs. What is the problem?

medium

A. The hour value 25 is invalid in cron syntax

B. The script path is incorrect

C. The minute value 0 is invalid

D. Cron jobs cannot run scripts

Solution

1. Step 1: Check the hour field in cron syntax

   The hour field must be between 0 and 23. 25 is invalid and causes the job not to run.

2. Step 2: Verify other options

   The script path might be correct, minute 0 is valid, and cron can run scripts, so only the hour value is the problem.

3. Final Answer:

   The hour value 25 is invalid in cron syntax -> Option A

4. Quick Check:

   Cron hour must be 0-23, 25 is invalid [OK]

Hint: Hour in cron is 0-23, not 25 [OK]

Common Mistakes:

• Using invalid hour values above 23
• Assuming minute 0 is wrong
• Thinking cron can't run scripts

5. You want to run a Python script every weekday at 7:15 AM on your Raspberry Pi. Which cron job entry is correct?

hard

A. 7 15 * * 1-5 /usr/bin/python3 /home/pi/script.py

B. 15 7 * * 1-5 /usr/bin/python3 /home/pi/script.py

C. 15 7 * * 6,7 /usr/bin/python3 /home/pi/script.py

D. 15 7 1-5 * * /usr/bin/python3 /home/pi/script.py

Solution

1. Step 1: Understand cron fields for time and days

   The format is minute hour day_of_month month day_of_week. To run at 7:15 AM, minute=15, hour=7. Weekdays are days 1-5 (Monday to Friday).

2. Step 2: Check each option

   15 7 * * 1-5 /usr/bin/python3 /home/pi/script.py correctly uses '15 7 * * 1-5' for 7:15 AM on weekdays. 7 15 * * 1-5 /usr/bin/python3 /home/pi/script.py swaps hour and minute. 15 7 * * 6,7 /usr/bin/python3 /home/pi/script.py uses weekend days (6,7). 15 7 1-5 * * /usr/bin/python3 /home/pi/script.py uses day_of_month 1-5, not weekdays.

3. Final Answer:

   15 7 * * 1-5 /usr/bin/python3 /home/pi/script.py -> Option B

4. Quick Check:

   Weekday cron = 1-5, time 7:15 = 15 7 [OK]

Hint: Weekdays are 1-5 in cron day_of_week field [OK]

Common Mistakes:

• Swapping hour and minute fields
• Using day_of_month instead of day_of_week for weekdays
• Confusing weekend days with weekdays