What is systemd?

systemd consists of these components:

  • systemd, which is the system and service manager
  • systemctl, a command line tool to interact with systemd
  • journald, a unified logging framework
  • logind, a daemon that handles user logins and seats
  • resolved, timesyncd, and networkd, which are responsible for network connection, domain name resolution and synchronizing time with internet resources

Managing existing services

A service is essentially a process, running in the background and managed/provisioned by systemd. Stuff you would like to run as services includes various servers (HTTP, SSH, FTP), synchronization utilities (Syncthing, rsync), virtualisation hypervisors (Docker, K8s), and many more. Let’s start by listing all available services on your system by running this command:

[s0x45ker--_(+_+)_--SysAdmin ~]$ systemctl

systemctl

Here is the structure of this table:

  • Name of the service. (Matches the name of the .service config file)
  • Current status of the service. loaded means systemd knows about it, active means systemd ran it successfully
  • Current status of the process. It indicates if the process is running or exited. Note that an active service can be exited (for example, 1 action has to happen at boot, and the process than returns. The service is still considered active.
  • Description

If you want to see some more details of a specific service, use this command:

[s0x45ker--_(+_+)_--SysAdmin ~]$ systemctl status dbus

systemctl-status

To start/stop services, use this:

systemctl start/stop <Service_Name>

Similarly, you can enable or disable the services. Enabled means it will run on boot:

systemctl enable/disable <SERVICE_NAME>

Creating your own services

I have created a script in /home/void/rabbit.py

#!/usr/bin/env python3
from time import sleep

import socket

HOST = '0.0.0.0'  # Standard loopback interface address (localhost)
PORT = 1234        # Port to listen on (non-privileged ports are > 1023)

message = 'Wake up, s0x45ker...\nThe Matrix has you...\nFollow the White Rabbit.\nKnock, Knock, s0x45ker.'

#for char in message:
#    print(char)

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.bind((HOST, PORT))
        s.listen()
        conn, addr = s.accept()
        with conn:
            print('Connected by', addr)

            for char in message:
                conn.send(bytes(char, 'utf-8'))
                sleep(0.3)

I created a service in cat /etc/systemd/system/rabbit.service

[Unit]
Description=Rabbit Service
After=network.target

[Service]
type=Simple
User=void
Restart=always
ExecStart=/usr/bin/env python3 /home/void/rabbit.py

[Install]
WantedBy=multi-user.target

this script simply creates a tcp service for everyone in the network and I use Netcat to connect to the service