Startup and init systems (systemd) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of checking a service status?

You run the command systemctl status sshd on a Linux system with systemd. What output will you see if the SSH service is active and running?

Linux CLI

systemctl status sshd

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

B sshd: command not found

C Active: inactive (dead)

D Active: active (running) since ...

💡 Hint

Think about what 'active and running' means in systemd service status.

When a service is running, systemctl shows 'Active: active (running)' with a timestamp. Other options indicate errors or inactive states.

💻 Command Output

intermediate

What happens when you enable a service?

You run systemctl enable nginx. What is the expected result?

Linux CLI

systemctl enable nginx

A Created symlink /etc/systemd/system/multi-user.target.wants/nginx.service → /lib/systemd/system/nginx.service.

B nginx.service is already running.

C Failed to enable unit: Unit file nginx.service does not exist.

D nginx service started successfully.

💡 Hint

Enabling a service creates links for automatic start, it does not start the service.

The enable command creates symbolic links so the service starts on boot. It does not start the service immediately.

🔧 Debug

advanced

Why does this systemd service fail to start?

Given this service file snippet, why will the service fail to start? [Service] ExecStart=/usr/bin/myapp Restart=always [Install] WantedBy=multi-user.target

Linux CLI

[Unit]
Description=My App Service

[Service]
ExecStart=/usr/bin/myapp
Restart=always

[Install]
WantedBy=multi-user.target

A The service file is missing the 'Type=' directive, causing systemd to not know how to manage the process.

B The ExecStart path is incorrect or the binary is missing, causing start failure.

C The [Unit] section is missing a required 'After=' directive.

D The [Install] section is missing 'Alias=' directive.

💡 Hint

Check if the executable path exists and is executable.

If the ExecStart path is wrong or the binary does not exist, systemd cannot start the service. The other options are not mandatory or cause different issues.

📝 Syntax

advanced

Identify the syntax error in this systemd service file

Which option shows the syntax error in this service file snippet? [Service] ExecStart=/usr/bin/myapp Restart=always RestartSec=5s TimeoutStartSec=30 User=appuser Group=appgroup [Install] WantedBy=multi-user.target

Linux CLI

[Service]
ExecStart=/usr/bin/myapp
Restart=always
RestartSec=5s
TimeoutStartSec=30
User=appuser
Group=appgroup

[Install]
WantedBy=multi-user.target

A User and Group directives must be in [Unit] section

B TimeoutStartSec=30 should be TimeoutStartSec=30s

C No syntax error; the file is valid

D RestartSec=5s should be RestartSec=5

💡 Hint

Check systemd documentation for valid directive formats and sections.

RestartSec accepts time with units like '5s'. TimeoutStartSec accepts seconds without units. User and Group belong in [Service]. This file is valid.

🚀 Application

expert

How to create a one-shot systemd service that runs a script once at boot?

You want to create a systemd service that runs a script /usr/local/bin/startup.sh only once during boot and then stops. Which service file configuration is correct?

A

[Unit]
Description=Run startup script once

[Service]
Type=oneshot
ExecStart=/usr/local/bin/startup.sh
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

B

[Unit]
Description=Run startup script once

[Service]
Type=simple
ExecStart=/usr/local/bin/startup.sh

[Install]
WantedBy=multi-user.target

C

[Unit]
Description=Run startup script once

[Service]
Type=forking
ExecStart=/usr/local/bin/startup.sh

[Install]
WantedBy=multi-user.target

D

[Unit]
Description=Run startup script once

[Service]
Type=idle
ExecStart=/usr/local/bin/startup.sh

[Install]
WantedBy=multi-user.target

💡 Hint

One-shot services run a command and then stop, optionally remaining active.

Type=oneshot tells systemd the service runs a short task and exits. RemainAfterExit=yes keeps the service active after the script finishes, useful for dependencies.

Practice

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

easy

A. To manage how the system starts and stops programs automatically

B. To edit text files in the system

C. To compile software from source code

D. To monitor network traffic

Solution

1. Step 1: Understand systemd's role

   systemd is a system and service manager that controls how programs start and stop on Linux.

2. Step 2: Compare options

   Only To manage how the system starts and stops programs automatically describes managing startup and shutdown of programs, which matches systemd's purpose.

3. Final Answer:

   To manage how the system starts and stops programs automatically -> Option A

4. Quick Check:

   systemd manages startup and shutdown = B [OK]

Hint: Remember: systemd controls startup and shutdown of services [OK]

Common Mistakes:

• Confusing systemd with text editors
• Thinking systemd compiles code
• Mixing systemd with network tools

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

easy

A. systemctl enable nginx

B. systemctl start nginx

C. systemctl status nginx

D. systemctl stop nginx

Solution

1. Step 1: Understand systemctl commands

   To enable a service to start at boot, the command is systemctl enable [service].

2. Step 2: Match command to action

   systemctl enable nginx uses enable with nginx, which is correct for auto-start.

3. Final Answer:

   systemctl enable nginx -> Option A

4. Quick Check:

   Enable means auto-start = A [OK]

Hint: Enable means auto-start at boot, start means immediate run [OK]

Common Mistakes:

• Using start instead of enable for auto-start
• Confusing status with enable
• Using stop instead of enable

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

medium

A. inactive

B. failed

C. active

D. unknown

Solution

1. Step 1: Understand systemctl is-active

   This command checks if a service is running and returns its state.

2. Step 2: Identify expected output when running

   If the SSH service is running, the output is active.

3. Final Answer:

   active -> Option C

4. Quick Check:

   Running service status = active [OK]

Hint: Active means running, inactive means stopped [OK]

Common Mistakes:

• Confusing active with inactive
• Expecting failed when service is running
• Thinking unknown means running

4. You run systemctl enable apache2 but the service does not start on boot. What is the most likely reason?

medium

A. The service is already running

B. You used start instead of enable

C. The systemctl command is not installed

D. The service file for apache2 is missing or incorrect

Solution

1. Step 1: Understand what enable does

   Enable creates links so the service starts at boot but does not start it immediately.

2. Step 2: Identify why enable might fail

   If the service file is missing or broken, enabling won't work properly, so it won't start on boot.

3. Final Answer:

   The service file for apache2 is missing or incorrect -> Option D

4. Quick Check:

   Missing service file blocks enable = D [OK]

Hint: Enable needs a valid service file to work [OK]

Common Mistakes:

• Confusing enable with start
• Assuming systemctl is missing
• Thinking running service means enable failed

5. You want to create a custom service that runs a script at startup. Which two steps must you perform to make sure it starts automatically with systemd?

hard

A. Add your script to /etc/rc.local and make it executable

B. Create a service file in /etc/systemd/system, then run 'systemctl enable yourservice' to auto-start it

C. Place your script in /usr/bin and reboot the system

D. Run 'systemctl start yourservice' and then 'systemctl status yourservice' only

Solution

1. Step 1: Create a systemd service file

   Write a service file describing your script and place it in /etc/systemd/system/ to define how systemd runs it.

2. Step 2: Enable the service

   Run systemctl enable yourservice to make it start automatically at boot.

3. Final Answer:

   Create a service file in /etc/systemd/system, then run 'systemctl enable yourservice' to auto-start it -> Option B

4. Quick Check:

   Create service file + enable = auto-start [OK]

Hint: Create service file and enable it to auto-start [OK]

Common Mistakes:

• Only starting service without enabling
• Using old /etc/rc.local method
• Placing script without service file