A Quick Recap

Systemd manages services through unit files, which define service behavior and configuration. These files are typically stored in /etc/systemd/system/ for user-defined services or /lib/systemd/system/ for system services. Each unit file contains directives specifying how the service should start, stop, and be managed.

Effective service management is essential for system administrators and users aiming to maintain a stable and efficient system. If you want to learn all the basics, I suggest you check out my earlier article, in which I delve deeply into these topics.

Constructing Basic Systemd Files

Let's start by constructing some basic Systemd files for common services and tools.

Systemd file for NGINX

This systemd file controls the Nginx web server, allowing it to be started, stopped, and reloaded as needed. It defines the command to execute and its dependencies.

First, open the file:

$ sudo nano /etc/systemd/system/nginx.service

The following would be the content:

[Unit]

Description=A high performance web server and a reverse proxy server

After=network.target

[Service]

Type=forking
ExecStart=/usr/sbin/nginx
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s TERM $MAINPID
PrivateTmp=true

[Install]
WantedBy=multi-user.target

Systemd file for Apache

This systemd service file manages the Apache HTTP server, ensuring it starts, stops, and reloads properly with the system. It defines the commands to control the server and its dependencies.

Open or create the file:

$ sudo nano /etc/systemd/system/apache2.service

And add the following content:

[Unit]

Description=The Apache HTTP Server

After=network.target


[Service]

Type=notify
ExecStart=/usr/sbin/apachectl -k start
ExecReload=/usr/sbin/apachectl -k graceful
ExecStop=/usr/sbin/apachectl -k stop
PrivateTmp=true


[Install]

WantedBy=multi-user.target

Systemd file for MySQL

This service file is responsible for managing the MySQL database server. It specifies how to start and stop the MySQL service and ensures it restarts on failure.

Open or create the file:

$ sudo nano /etc/systemd/system/mysql.service

Add the following content:

[Unit]

Description=MySQL Community Server

After=network.target


[Service]

Type=simple
User=mysql
Group=mysql
ExecStart=/usr/bin/mysqld_safe
Restart=on-failure


[Install]

WantedBy=multi-user.target

Systemd file for Redis

This service file manages the Redis in-memory data store, specifying how to start and stop the service while ensuring it runs under the correct user and group.

Open or create the file:

$ sudo nano /etc/systemd/system/redis.service

Add the following content:

[Unit]

Description=Redis In-Memory Data Store

After=network.target


[Service]

User=redis
Group=redis
ExecStart=/usr/bin/redis-server /etc/redis/redis.conf
ExecStop=/usr/bin/redis-cli shutdown


[Install]

WantedBy=multi-user.target

Systemd file for SSH

This file is usually present by default in most Linux configs by default. But for information's sake, I’ll still go over it. This file manages the OpenSSH server, allowing secure remote access to the system. It defines how to start the SSH daemon and ensures it restarts if there are failures.

Open the file:

$ sudo nano /etc/systemd/system/ssh.service

It should have the following content:

[Unit]

Description=OpenSSH Server

After=network.target


[Service]

ExecStart=/usr/bin/sshd -D
Restart=on-failure


[Install]

WantedBy=multi-user.target

Systemd file for Cron

This file is also typically included by default in most Linux configurations. However, for the sake of completeness, I'll still discuss it. This systemd service file controls the cron daemon, which is responsible for executing scheduled tasks on the system. It defines how the cron service should run.

Open the file:

$ sudo nano /etc/systemd/system/crond.service

The following should be the content:

[Unit]

Description=Regular background program processing daemon


[Service]

ExecStart=/usr/sbin/crond -n


[Install]

WantedBy=multi-user.target

Systemd file for a Node.js Application

This file manages a Node.js application, specifying how to start it and ensuring it restarts on failure while running under a specified user.

Open or create the file:

$ sudo nano /etc/systemd/system/my-node-app.service

Add the following content. Ensure to make changes to it accordingly:

[Unit]

Description=My Node.js Application

After=network.target


[Service]

ExecStart=/usr/bin/node /path/to/my/app.js
Restart=always
User=nodeuser
Environment=NODE_ENV=production


[Install]

WantedBy=multi-user.target

Enabling Systemd Services

When you want a service to launch automatically every time your system boots up, you need to enable it. This process tells the system to include the service in its startup routine. To make this happen, enter the following command:

$ sudo systemctl enable <service_name>

So, to enable the NGINX service from the examples above, simply run:

$ sudo systemctl enable nginx

Creating this symbolic link connects the NGINX service file to the system's startup sequence. By doing so, you're essentially telling your server to fire up NGINX whenever it boots. It's a nifty trick for making sure your web server is always ready to go without you having to manually start it each time.

Disabling Systemd Services

Disabling a service prevents it from starting automatically at boot. To disable a service, use:

$ sudo systemctl disable <service_name>

To disable the NGINX service as mentioned in the examples above, just execute:

$ sudo systemctl disable nginx

This command removes the startup link for NGINX. As a result, the web server will no longer launch automatically when the system boots. You'll need to start nginx manually when you want to use it.

Starting and Stopping Systemd Services

When you start a service, you run it immediately on your system. Stopping it halts its operation. These actions affect the current session only. When you enable a service, you set it to launch automatically at every system startup.

Disabling prevents this automatic start. Start and stop controlling the service now while enabling and disabling determine its behavior on future reboots. You can manually start or stop services using the following commands -

To start a service:

$ sudo systemctl start <service_name>

To stop a service:

$ sudo systemctl stop <service_name>

So, for the above example, these should be the right commands for the same actions:

$ sudo systemctl start nginx
$ sudo systemctl stop nginx

Checking the Status of Systemd Services

To verify if a service is operating properly, you can check its status. Use this command to view the current state of a service:

$ sudo systemctl status <service_name>

For the above example, it should be:

$ sudo systemctl status nginx

When you run this command, you'll see a quick report on the service. It tells you if the service is currently active and running, stopped and inactive, or if it has encountered any failures.

Masking Systemd Services

And finally, systemd masking offers a robust method to prevent unit activation, surpassing the standard disable function. By linking a unit to /dev/null, masking renders it inert, blocking both manual and automatic starts.

This proves invaluable when managing conflicting services or permanently deactivating unnecessary units. Unlike disabling, which merely prevents automatic startup, masking ensures complete inactivation.

System administrators often employ this technique to maintain system stability and security. The process is reversible through unmasking, restoring the unit's potential for activation when needed.

To mask a service, use:

$ sudo systemctl mask <service_name>

To completely prevent the NGINX service from running, you would execute:

$ sudo systemctl mask nginx

To unmask the service, simply use:

$ sudo systemctl unmask nginx

To Wrap Up

Understanding Systemd unit files is key for managing Linux services effectively. By creating and configuring these files, you ensure services run smoothly and meet your system's needs. Learning to enable, disable, start, stop, and mask services helps maintain a stable system.

As you explore Systemd further, you'll improve your admin skills and boost server reliability. Using these practices will help you streamline your work and improve performance in your Linux setup.

Meet Aayush, a WordPress website designer with almost a decade of experience who crafts visually appealing websites and has a knack for writing engaging technology blogs. In his spare time, he enjoys illuminating the minds around him.