Editing crontab (crontab -e) in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to open the crontab editor for the current user.

Linux CLI

crontab [1]

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

A-r

B-l

C-e

D-v

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-l' which lists the crontab instead of editing it.

Using '-r' which removes the crontab instead of editing.

The '-e' option opens the crontab editor for the current user.

2fill in blank

medium

Complete the crontab line to run a script every day at 5 AM.

Linux CLI

[1] 5 * * * /home/user/script.sh

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

A0

B5

C30

D15

Attempts:

3 left

💡 Hint

Common Mistakes

Putting 5 in the minutes field instead of the hour field.

Using 30 or 15 which run at 5:15 or 5:30 instead of 5:00.

The first field is minutes, so '0' means at minute zero of the hour (5:00 AM).

3fill in blank

hard

Fix the error in this crontab line to run a backup script every Sunday at midnight.

Linux CLI

0 0 * * [1] /usr/local/bin/backup.sh

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

A7

Bsun

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 7 which may not be supported on all systems.

Using 0 which can mean Sunday but is less readable.

The day of week field can be 'sun' to represent Sunday, which is clearer and valid.

4fill in blank

hard

Fill both blanks to run a cleanup script every 15 minutes.

Linux CLI

*/[1] * * * [2] /home/user/cleanup.sh

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

A15

B*

D*/15

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*/15' in the hour field which is invalid.

Using '*' in the minutes field which runs every minute.

The minutes field uses '*/15' for every 15 minutes, so '15' is correct for the first blank and '*' for the day-of-week field means every day of the week.

5fill in blank

hard

Fill all three blanks to run a script at 2:30 PM on the first day of every month.

Linux CLI

[1] [2] [3] * * /home/user/monthly_report.sh

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

A30

B14

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 instead of 14 for the hour field.

Using 0 for the day of month which is invalid.

The minutes field is 30, hour is 14 (2 PM in 24-hour format), and day of month is 1 for the first day.

Practice

1. What does the command crontab -e do in Linux?

easy

A. It deletes all cron jobs for the current user.

B. It lists all scheduled cron jobs for all users.

C. It runs the cron daemon immediately.

D. It opens the current user's cron jobs for editing.

Solution

1. Step 1: Understand the purpose of crontab -e

   This command opens the cron table for the current user in an editor so you can add or change scheduled tasks.

2. Step 2: Compare with other options

   crontab -l lists jobs, not edits. Deleting or running the daemon are different commands.

3. Final Answer:

   It opens the current user's cron jobs for editing. -> Option D

4. Quick Check:

   crontab -e = edit cron jobs [OK]

Hint: Remember: '-e' means edit your cron jobs [OK]

Common Mistakes:

• Confusing '-e' with '-l' which lists jobs
• Thinking it deletes cron jobs
• Assuming it runs cron immediately

2. Which of the following is the correct syntax to schedule a cron job to run every day at 3:30 AM using crontab -e?

easy

A. 30 3 * * * /path/to/script.sh

B. 3 30 * * * /path/to/script.sh

C. * 3 30 * * /path/to/script.sh

D. 30 03 * * /path/to/script.sh

Solution

1. Step 1: Understand cron time fields order

   The order is: minute hour day-of-month month day-of-week. So 30 3 means 3:30 AM.

2. Step 2: Check each option

   30 3 * * * /path/to/script.sh correctly uses '30 3' for 3:30 AM daily. 3 30 * * * /path/to/script.sh swaps minute and hour. * 3 30 * * /path/to/script.sh misplaces day and minute. 30 03 * * /path/to/script.sh misses a field.

3. Final Answer:

   30 3 * * * /path/to/script.sh -> Option A

4. Quick Check:

   Minute Hour Day Month Weekday = 30 3 * * * [OK]

Hint: Minute comes before hour in cron syntax [OK]

Common Mistakes:

• Swapping hour and minute fields
• Missing one of the five time fields
• Using leading zeros incorrectly

3. After adding this line in crontab -e:
0 0 * * 0 /home/user/backup.sh
What will happen?

medium

A. The script runs every day at midnight.

B. The script runs every Sunday at midnight.

C. The script runs every hour on Sundays.

D. The script runs once a month at midnight.

Solution

1. Step 1: Decode the cron schedule

   Fields: minute=0, hour=0, day-of-month=*, month=*, day-of-week=0. Day-of-week 0 means Sunday.

2. Step 2: Interpret the schedule

   The script runs at 00:00 (midnight) on every Sunday.

3. Final Answer:

   The script runs every Sunday at midnight. -> Option B

4. Quick Check:

   0 0 * * 0 = Sunday midnight [OK]

Hint: Day-of-week 0 means Sunday in cron [OK]

Common Mistakes:

• Thinking it runs daily instead of weekly
• Confusing day-of-month with day-of-week
• Assuming 0 means Monday

4. You added this line in crontab -e:
60 12 * * * /home/user/script.sh
Why does this cron job not run?

medium

A. Script path must be absolute, this is relative.

B. Hour 12 is invalid; hours range 0-11.

C. Minute value 60 is invalid; minutes range 0-59.

D. Missing day-of-week field causes error.

Solution

1. Step 1: Check the minute field validity

   Minutes must be between 0 and 59. 60 is invalid and causes cron to ignore the job.

2. Step 2: Verify other fields

   Hour 12 is valid (means noon). Day-of-week is optional. Script path is absolute.

3. Final Answer:

   Minute value 60 is invalid; minutes range 0-59. -> Option C

4. Quick Check:

   Minute must be 0-59, 60 is invalid [OK]

Hint: Minutes max at 59, not 60 [OK]

Common Mistakes:

• Using 60 as a minute value
• Confusing 12-hour clock with 24-hour
• Thinking day-of-week is mandatory

5. You want to run a backup script every weekday at 11:45 PM using crontab -e. Which line correctly schedules this?

hard

A. 45 23 * * 1-5 /home/user/backup.sh

B. 23 45 * * 1-5 /home/user/backup.sh

C. 45 23 * * 0-6 /home/user/backup.sh

D. 45 11 * * 1-5 /home/user/backup.sh

Solution

1. Step 1: Understand the time and days needed

   11:45 PM is hour 23, minute 45. Weekdays are Monday(1) to Friday(5).

2. Step 2: Check each option's correctness

   45 23 * * 1-5 /home/user/backup.sh uses '45 23' for 11:45 PM and '1-5' for weekdays correctly. 23 45 * * 1-5 /home/user/backup.sh swaps minute and hour. 45 23 * * 0-6 /home/user/backup.sh runs every day. 45 11 * * 1-5 /home/user/backup.sh uses hour 11 (11 AM) instead of 23.

3. Final Answer:

   45 23 * * 1-5 /home/user/backup.sh -> Option A

4. Quick Check:

   Minute Hour Days 1-5 = 45 23 Mon-Fri [OK]

Hint: Hour 23 = 11 PM; weekdays 1-5 [OK]

Common Mistakes:

• Swapping hour and minute fields
• Using 11 instead of 23 for PM
• Using 0-6 instead of 1-5 for weekdays