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:

1. To start the machine:

    vagrant up
   

2. To reload (halt and up):

    vagrant reload
   

3. To check VM deployment use:

    vagrant global-status --prune
   

4. To ssh into the machine use:

    vagrant ssh ubuntu
   

Create custom Linux service:

1. 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

2. 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
   

3. 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
   

4. 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
   

5. Start the service:

    sudo systemctl start <service_name>
   

6. Check the status of the service:

    sudo systemctl status <service_name>
   

7. To enable service on machine startup when the system boots use:

    sudo systemctl enable <service_name>
   

8. To stop and restart service use:

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

References:

1. What is systemd?

2. systemctl Commands: Restart, Reload, and Stop Service

3. Vagrant templates

4. Systemd service options