systemd service starting without login of user

I recently had to start a systemd process without having a user being logged in. The systemd process was starting, but unfortunately the network was not up and running. The issue was that the wifi was linked to the user. In this case I used ArchLinux (Manjaro)

Here are the steps to start a service fully automatically.
Create a service-file in the location /etc/systemd/system/myService.service

[Unit]
Description=myService
After=network-online.target
Wants=network-online.target
AssertFileNotEmpty=/opt/myService/config.json

[Service]
Type=simple
SyslogIdentifier=myService
WorkingDirectory=/opt/myService
ExecStart=/opt/MyService/myexecutable (or script)
RemainAfterExit=true
Restart=always
Nice=-20

[Install]
WantedBy=multi-user.target

Once created enable the service. This will enable the service startup of the system.

sudo systemctl enable myService.service
sudo systemctl daemon-reload
sudo systemctl restart myService.service

In order to check the logs of your service use the following command:

# Just use the journalctl command, as in:
journalctl -u service-name.service

# Or, to see only log messages for the current boot:
journalctl -u service-name.service -b

Adjust the following script /etc/NetworkManager/system-connections
Change the connection of your linux.

[connection]
id=MyHotspot
uuid=exxxxxxxx-xxxxxxxxx
type=wifi
permissions=

[wifi]
mac-address=00:XX:XX:XX:DF:ED
mac-address-blacklist=
mode=infrastructure
ssid=My SSID

[wifi-security]
auth-alg=open
key-mgmt=wpa-psk
psk=MYPASSWORD

[ipv4]
dns-search=
method=auto

[ipv6]
addr-gen-mode=stable-privacy
dns-search=
method=auto

Important here is thepermissions=.In a previous version of the file it was mentioning a few users. So the wifi only came up at login time of the users. With permissions= it starts even without anybody logging in.

Headless Raspberry Pi

Step 1. Download a lite Raspbian image

Download the version you need. As we want to install a headless version download the Raspian XXXXX Lite version.

Step 2. Copy the image

From a Linux terminal use the following command to find your SD Card:

sudo fdisk -l

This will show you something like

Disk /dev/sdc 14.86 Gib ......

Ensure you select here the correct disk.

Afterwards copy the image with the following comand. Replace /dev/sdX by the correct path.

sudo dd bs=4M if=2019-07-10-raspbian-buster.img of=/dev/sdX conv=fsync

Step 3. Enable ssh

To activate ssh at the first start you just have to create a file ssh in the boot folder.

touch /run/media/your_username/boot/ssh

The path above might be different on your system.

Step 4. Add network info

Create a file in /run/media/your_username/boot/ called: wpa_supplicant.conf.

sudo nano /run/media/your_username/boot/wpa_supplicant.conf

Then paste the following into it (replace your country code, SSID and Password):

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev 
update_config=1 
ap_scan=1 
fast_reauth=1 
country=JP 
network=
{ ssid="network SSID" 
  psk="network password" 
  id_str="0" 
  priority=100 
}

Step 5. Find your Raspberry Pi in your network

One solution is to login to your router.

In case you do not have access to your router you can scan your ip range with nmap. Use the following command and search for your Raspberry Pi:

sudo nmap -sP 192.168.0.0/24

Adjust 192.168.0.0 to your ip range. In many cases it is 192.168.1.0 or 192.168.100.0

Step 6. Login to your Raspberry Pi

Use the following command to login:

ssh pi@192.168.0.150

Password by default: raspberry

ip route for wifi

In case you want to route the traffic of your linux machine of a specific IP through a specific interface ip routecommand should be used.

One example below asuming wlp2s0 is your wifi.

sudo ip route add 155.100.200.0/24 via 192.168.1.1 dev wlp2s0

This will lead all the traffic with target ip range 155.100.200.0/24 trough the interface of your wifi (assuming 192.168.1.1 is the wifi router).

I did not yet found a solution to route the traffic of a target “domain” through a specific interface. Happy for any input.