systemd timers in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of systemd timer status command

What is the output of the command systemctl status mytask.timer if the timer is active and scheduled to run the next job in 10 minutes?

Linux CLI

systemctl status mytask.timer

A

● mytask.timer - Run mytask periodically
   Loaded: loaded (/etc/systemd/system/mytask.timer; enabled; vendor preset: enabled)
   Active: active (waiting) since Fri 2024-06-21 10:00:00 UTC; 5min ago
   Trigger: Fri 2024-06-21 10:15:00 UTC; 10min left

B

● mytask.timer - Run mytask periodically
   Loaded: loaded (/etc/systemd/system/mytask.timer; disabled; vendor preset: enabled)
   Active: inactive (dead)

C

● mytask.timer - Run mytask periodically
   Loaded: loaded (/etc/systemd/system/mytask.timer; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Fri 2024-06-21 09:50:00 UTC; 15min ago

D

● mytask.timer - Run mytask periodically
   Loaded: not-found (Reason: No such file or directory)
   Active: inactive (dead)

💡 Hint

Look for the 'Active: active (waiting)' status and the next trigger time.

When a systemd timer is active and waiting to trigger, the status shows 'active (waiting)' and the next trigger time with a countdown.

🧠 Conceptual

intermediate

Understanding systemd timer units and service units

Which statement correctly describes the relationship between a systemd timer unit and its corresponding service unit?

A Timer units and service units are independent and do not interact.

B A service unit schedules the timer unit to run at specific times.

C A timer unit triggers the execution of its linked service unit according to the schedule defined in the timer.

D A timer unit replaces the need for a service unit entirely.

💡 Hint

Think about what triggers the service execution in systemd timers.

A systemd timer unit schedules when its linked service unit runs. The timer triggers the service based on the timer's schedule.

📝 Syntax

advanced

Identify the correct OnCalendar syntax for a systemd timer

Which option correctly sets a systemd timer to run every day at 3:30 AM using the OnCalendar directive?

Linux CLI

[Timer]
OnCalendar=???

A daily 03:30

B 03:30 daily

C daily

D 03:30:00

💡 Hint

OnCalendar uses a specific time format like 'HH:MM:SS' or calendar events.

The correct OnCalendar syntax for 3:30 AM daily is '03:30:00'. 'daily' alone means midnight. Other options are invalid formats.

🔧 Debug

advanced

Why does this systemd timer not trigger the service?

Given the following timer unit file, why does the timer never trigger the service? [Unit] Description=Run backup daily [Timer] OnCalendar=daily Persistent=true [Install] WantedBy=timers.target

Linux CLI

[Service]
ExecStart=/usr/local/bin/backup.sh

A The timer unit file is missing the [Service] section; the service is not defined here.

B The OnCalendar=daily syntax is invalid and causes the timer to fail silently.

C The Persistent=true option disables the timer from running if missed.

D The WantedBy=timers.target is incorrect; it should be multi-user.target.

💡 Hint

Timers trigger service units, but the service unit must be defined separately.

The timer unit file should not contain a [Service] section; the service must be defined in a separate .service file. Without a service unit, the timer has nothing to trigger.

🚀 Application

expert

Create a systemd timer to run a script every 15 minutes starting at 5 minutes past the hour

Which OnCalendar value correctly schedules a systemd timer to run every 15 minutes starting at 5 minutes past each hour (e.g., 00:05, 00:20, 00:35, 00:50)?

A OnCalendar=*-*-* *:05,20,35,50:00

B OnCalendar=*-*-* *:05/15:00

C OnCalendar=*-*-* *:5/15:00

D OnCalendar=*:05/15:00

💡 Hint

Use the format 'HH:MM/interval:SS' with leading zeros for minutes.

The correct syntax uses '05/15' to start at 5 minutes and repeat every 15 minutes. Leading zeros are required for minutes. Other options are invalid or incorrectly formatted.