systemctl for service management in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is systemctl used for in Linux?

systemctl is a command-line tool to control and manage system services and the system state on Linux systems using systemd.

beginner

How do you start a service named nginx using systemctl?

Use the command systemctl start nginx. This starts the nginx service immediately.

beginner

What does the command systemctl enable apache2 do?

It sets the apache2 service to start automatically when the system boots up.

beginner

How can you check the status of a service called ssh?

Run systemctl status ssh to see if the service is active, inactive, or failed, along with recent logs.

intermediate

What is the difference between systemctl stop and systemctl disable?

systemctl stop stops a service immediately. systemctl disable prevents the service from starting automatically at boot.

Which command starts a service immediately?

A systemctl start service_name

B systemctl enable service_name

C systemctl status service_name

D systemctl disable service_name

systemctl start starts the service right away. enable only sets it to start on boot.

What does systemctl status show?

A Enable a service at boot

B Stop a running service

C Current state and logs of a service

D Restart a service

systemctl status shows if the service is running and recent log messages.

How do you prevent a service from starting automatically on boot?

A systemctl enable service_name

B systemctl stop service_name

C systemctl start service_name

D systemctl disable service_name

disable removes the service from automatic startup.

Which command restarts a service?

A systemctl restart service_name

B systemctl status service_name

C systemctl stop service_name

D systemctl enable service_name

restart stops and then starts the service again immediately.

If you want to see if a service is active or failed, which command do you use?

A systemctl enable service_name

B systemctl status service_name

C systemctl disable service_name

D systemctl start service_name

status shows the current state of the service.

Explain how to start, stop, enable, and check the status of a service using systemctl.

Think about the commands you use to control a service's running state and boot behavior.

Describe the difference between stopping a service and disabling a service with systemctl.

Consider what happens now versus what happens on the next reboot.

Practice

1. What does the command systemctl start nginx do on a Linux system?

easy

A. It disables the nginx service from starting at boot.

B. It stops the nginx service.

C. It shows the status of the nginx service.

D. It starts the nginx service immediately.

Solution

1. Step 1: Understand the start action in systemctl

   The start command tells systemctl to begin running the specified service immediately.

2. Step 2: Apply to nginx service

   Using systemctl start nginx will start the nginx service right away, without affecting boot settings.

3. Final Answer:

   It starts the nginx service immediately. -> Option D

4. Quick Check:

   start means run service now [OK]

Hint: Start means run the service now, not stop or status [OK]

Common Mistakes:

• Confusing start with stop or restart
• Thinking start changes boot behavior
• Using start to check status

2. Which of the following is the correct syntax to enable a service named httpd to start automatically at boot?

easy

A. systemctl enable start httpd

B. systemctl httpd enable

C. systemctl enable httpd

D. systemctl start enable httpd

Solution

1. Step 1: Identify the correct command structure for enabling services

   The correct syntax is systemctl enable <service-name> to set a service to start at boot.

2. Step 2: Match the syntax with the httpd service

   Using systemctl enable httpd correctly enables the httpd service at boot time.

3. Final Answer:

   systemctl enable httpd -> Option C

4. Quick Check:

   enable <service> sets boot start [OK]

Hint: Enable command is followed directly by service name [OK]

Common Mistakes:

• Adding extra words like 'start' with enable
• Wrong order of commands
• Using start instead of enable for boot

3. What will be the output of the command systemctl status sshd if the SSH service is running?

medium

A. Active: active (running) since [date and time]

B. Failed to start sshd.service: Unit not found.

C. Inactive (dead)

D. No output is shown.

Solution

1. Step 1: Understand what systemctl status shows

   This command displays the current state of the service, including if it is running or stopped.

2. Step 2: Interpret the output for a running sshd service

   If sshd is running, the output includes a line like Active: active (running) since ... showing it is up.

3. Final Answer:

   Active: active (running) since [date and time] -> Option A

4. Quick Check:

   Status shows running state if active [OK]

Hint: Look for 'Active: active (running)' in status output [OK]

Common Mistakes:

• Expecting no output when service runs
• Confusing 'inactive' with running
• Thinking error means service is running

4. You run systemctl start apache2 but get the error: Failed to start apache2.service: Unit apache2.service not found. What is the most likely cause?

medium

A. The service name is incorrect or does not exist.

B. The apache2 service is already running.

C. You need to use restart instead of start.

D. You must run the command without sudo.

Solution

1. Step 1: Analyze the error message

   The error says the unit (service) apache2.service was not found, meaning systemctl cannot locate it.

2. Step 2: Identify the cause

   This usually means the service name is wrong or the service is not installed on the system.

3. Final Answer:

   The service name is incorrect or does not exist. -> Option A

4. Quick Check:

   Unit not found means wrong or missing service [OK]

Hint: Check service name spelling if 'Unit not found' error appears [OK]

Common Mistakes:

• Assuming service is running despite error
• Trying restart instead of start without checking
• Running without sudo causing permission error

5. You want to ensure the docker service starts automatically on boot and is currently running. Which two commands should you run in order, to achieve this?

hard

A. systemctl enable docker; systemctl status docker

B. systemctl start docker; systemctl enable docker

C. systemctl restart docker; systemctl disable docker

D. systemctl stop docker; systemctl enable docker

Solution

1. Step 1: Understand the goal

   We want to ensure the docker service is currently running and starts automatically on boot.

2. Step 2: Choose commands to enable boot start and ensure running

   Running systemctl start docker ensures the service is running (safe if already running), then systemctl enable docker sets it to start at boot.

3. Final Answer:

   systemctl start docker; systemctl enable docker -> Option B

4. Quick Check:

   Start first, then enable for boot start [OK]

Hint: Start service first, then enable it for boot [OK]

Common Mistakes:

• Enabling before starting service
• Stopping service when wanting it running
• Disabling service by mistake