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.