systemd timers in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a systemd timer named backup.timer.

Linux CLI

sudo systemctl [1] backup.timer

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

Aenable

Bstart

Cstop

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'enable' only sets the timer to start on boot but does not start it immediately.

Using 'stop' or 'status' does not start the timer.

The start command activates the timer immediately.

2fill in blank

medium

Complete the code to check the status of a systemd timer named cleanup.timer.

Linux CLI

systemctl [1] cleanup.timer

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

Arestart

Bdisable

Cstatus

Dreload

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'restart' will restart the timer but does not show status.

Using 'disable' stops the timer from starting on boot.

Using 'reload' reloads configuration but does not show status.

The status command shows the current state and recent logs of the timer.

3fill in blank

hard

Fix the error in the command to enable a timer named sync.timer.

Linux CLI

sudo systemctl [1] sync.timer

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

Aenable

Bstop

Cdisable

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' only runs the timer now but does not enable it on boot.

Using 'disable' or 'stop' will prevent the timer from running.

The enable command sets the timer to start automatically at boot.

4fill in blank

hard

Fill both blanks to create a systemd timer file snippet that runs a service every 10 minutes.

Linux CLI

[Timer]
OnUnitActiveSec=[1]
Unit=[2]

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

A10min

Bbackup.service

C10m

Dcleanup.service

Attempts:

3 left

💡 Hint

Common Mistakes

Using '10min' is not a valid time format for systemd timers.

Specifying the wrong service name will not trigger the intended service.

Use 10m for 10 minutes interval and specify the service to run with Unit=backup.service.

5fill in blank

hard

Fill all three blanks to create a systemd timer file snippet that runs a service daily at 2:30 AM.

Linux CLI

[Timer]
OnCalendar=[1]
Unit=[2]
Persistent=[3]

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

Adaily

Bbackup.service

Ctrue

D2:30

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'daily' schedules the timer at midnight instead of 2:30 AM.

Leaving Persistent off may cause missed runs if the system was off.

Use 2:30 for daily at 2:30 AM schedule, specify the service with backup.service, and set Persistent=true to catch missed runs.

Practice

1. What is the main purpose of a systemd timer in Linux?

easy

A. To manage user permissions

B. To schedule and run tasks automatically at specified times

C. To monitor system hardware status

D. To update software packages automatically

Solution

1. Step 1: Understand systemd timer role

   Systemd timers are designed to schedule tasks to run automatically without manual intervention.

2. Step 2: Compare with other options

   Monitoring hardware, managing permissions, and updating packages are not the primary roles of systemd timers.

3. Final Answer:

   To schedule and run tasks automatically at specified times -> Option B

4. Quick Check:

   Systemd timers = schedule tasks [OK]

Hint: Timers schedule tasks like alarms for programs [OK]

Common Mistakes:

• Confusing timers with monitoring tools
• Thinking timers manage user permissions
• Assuming timers update software automatically

2. Which of the following is the correct syntax to enable a systemd timer named backup.timer?

easy

A. systemctl enable backup.timer

B. systemctl start backup.timer

C. systemctl run backup.timer

D. systemctl activate backup.timer

Solution

1. Step 1: Identify enabling command for systemd timers

   The command systemctl enable sets a timer to start automatically on boot.

2. Step 2: Differentiate from other commands

   start runs the timer immediately but does not enable it; run and activate are invalid commands.

3. Final Answer:

   systemctl enable backup.timer -> Option A

4. Quick Check:

   Enable timer = systemctl enable [OK]

Hint: Use 'enable' to start timer on boot, 'start' to run now [OK]

Common Mistakes:

• Using 'start' instead of 'enable' to auto-run timers
• Using invalid commands like 'run' or 'activate'
• Confusing service commands with timer commands

3. Given this timer unit file snippet:

[Timer]
OnCalendar=*-*-* 12:00:00
Persistent=true

What does the Persistent=true setting do?

medium

A. Prevents the timer from running at boot

B. Runs the timer only once

C. Disables the timer after one run

D. Runs missed jobs immediately after boot

Solution

1. Step 1: Understand Persistent=true meaning

   This setting makes systemd run any missed timer jobs immediately after the system boots.

2. Step 2: Eliminate other options

   It does not limit runs to once, disable timers, or prevent running at boot.

3. Final Answer:

   Runs missed jobs immediately after boot -> Option D

4. Quick Check:

   Persistent=true = catch missed runs after reboot [OK]

Hint: Persistent=true runs missed tasks after reboot [OK]

Common Mistakes:

• Thinking it runs only once
• Assuming it disables timer after run
• Believing it prevents timer at boot

4. You created a timer file cleanup.timer but it never triggers the service. Which is the most likely mistake?

medium

A. The timer file is not named exactly like the service file

B. The timer file is missing the [Timer] section

C. The service file cleanup.service is not enabled

D. The timer file uses OnBootSec= instead of OnCalendar=

Solution

1. Step 1: Check timer and service file naming

   Systemd timers must have matching names with their service files except for the extension.

2. Step 2: Analyze other options

   Missing [Timer] section causes syntax errors; service enabling is not required for timers to trigger; both OnBootSec and OnCalendar are valid.

3. Final Answer:

   The timer file is not named exactly like the service file -> Option A

4. Quick Check:

   Timer and service names must match [OK]

Hint: Timer and service filenames must match except extension [OK]

Common Mistakes:

• Ignoring filename matching between timer and service
• Assuming service must be enabled for timer to run
• Confusing valid timer options as errors

5. You want a systemd timer to run a backup service every day at 3:30 AM but only if the system was off at that time. Which timer configuration achieves this?

hard

A. [Timer]
OnActiveSec=03:30:00
Persistent=true

B. [Timer]
OnCalendar=*-*-* 03:30:00
AccuracySec=1min

C. [Timer]
OnCalendar=*-*-* 03:30:00
Persistent=true

D. [Timer]
OnBootSec=03:30:00
Persistent=false

Solution

1. Step 1: Identify daily schedule at 3:30 AM

   The OnCalendar=*-*-* 03:30:00 sets the timer to run daily at 3:30 AM.

2. Step 2: Ensure missed runs execute after downtime

   Persistent=true makes systemd run missed jobs after system was off at scheduled time.

3. Step 3: Evaluate other options

   AccuracySec adjusts timing precision but doesn't affect missed runs; OnBootSec and OnActiveSec run relative to boot or activation, not fixed time.

4. Final Answer:

   [Timer] OnCalendar=*-*-* 03:30:00 Persistent=true -> Option C

5. Quick Check:

   Daily 3:30 AM with catch-up = OnCalendar + Persistent [OK]

Hint: Use OnCalendar with Persistent=true for daily missed runs [OK]

Common Mistakes:

• Using OnBootSec instead of OnCalendar for fixed time
• Forgetting Persistent=true to run missed jobs
• Confusing AccuracySec with scheduling behavior