What is systemd and systemctl?

systemd is a Linux initialization system and service manager. systemd provides a logging daemon and other tools and utilities to help with common system administration tasks.

Its primary component is a "system and service manager" — an init system used to bootstrap user space and manage user processes.

systemctl - is a controlling interface and inspection tool for the systemd. You use this tool to perform administrative tasks and interact with systemd.

Prerequisites:

For demo purposes use the following Vagrantfile to create an Ubuntu-based machine:

Vagrant.configure("2") do |config|

  # VM machine configuration
  config.vm.provider :virtualbox do |v|
    v.customize ["modifyvm", :id, "--memory", 2048]
    # v.customize ["modifyvm", :id, "--cpus", 2]
  end

  # Ubuntu worker node
  config.vm.define "ubuntu" do |ubuntu|
    ubuntu.vm.box = "ubuntu/bionic64"
    ubuntu.vm.hostname = "ubuntu"
  end

end

Basic Vagrant commands:

To start the machine:
```
 vagrant up
```
To reload (halt and up):
```
 vagrant reload
```
To check VM deployment use:
```
 vagrant global-status --prune
```
To ssh into the machine use:
```
 vagrant ssh ubuntu
```

Create custom Linux service:

As a demo use the following script `custom_service.sh` Bash script file:

 DATE=`date '+%Y-%m-%d %H:%M:%S'`
 echo "Custom service started at ${DATE}" | systemd-cat -p info

 while :
 do
 echo "Looping...";
 sleep 30;
 done

The script logs the time and runs every 30 seconds

Move the script to /usr/bin/ and make it executable:

 sudo mv custom_service.sh /usr/bin/custom_service.sh
 sudo chmod +x /usr/bin/custom_service.sh

Create a Unit file to define a systemd service:

 [Unit]
 Description=Custom systemd service.

 [Service]
 Type=simple
 ExecStart=/bin/bash /usr/bin/custom_service.sh

 [Install]
 WantedBy=multi-user.target

Move the unit file to /etc/systemd/system and give it permissions:

 sudo mv <service_name>.service /etc/systemd/system/<service_name>.service
 sudo chmod 644 /etc/systemd/system/<service_name>.service

Start the service:
```
 sudo systemctl start <service_name>
```
Check the status of the service:
```
 sudo systemctl status <service_name>
```
To enable service on machine startup when the system boots use:
```
 sudo systemctl enable <service_name>
```

To stop and restart service use:

 sudo systemctl stop <service_name>
 sudo systemctl restart <service_name>

How to create a custom Linux service via systemd

What is systemd and systemctl?

Prerequisites:

Create custom Linux service:

References: