Windows

In the main Hydra directory there's a WindowsService subfolder which contains batch scripts to install and uninstall Hydra as a service. Run them as administrator.

Linux

In the main Hydra directory there are two folders systemd and upstart. Check them out. Take the scripts as a pointer. I'm not a linux expert.

Ubuntu/LinixMint 20 - `systemd` install

Assumptions

You know basic Linux commands in the terminal
You know how to edit a file
You have python 3 installed

This is more of a rough guideline.

High Level Steps

Create a system account called nzbhydra2
Copy over executables and conf files
Edit nzbhydra2 service
Install Service

Create nzbhydra2 system account:

sudo adduser --system --no-create-home --group nzbhydra2

Install nzbhydra2 to /opt:

cd /tmp
tag=$(curl -s https://api.github.com/repos/theotherp/nzbhydra2/releases/latest  | grep '"tag_name":' | sed -E 's/.*"([^"]+)".*/\1/')
tag_no_v=${tag#v}
curl -L -o nzbhydra2-latest.zip "https://github.com/theotherp/nzbhydra2/releases/download/$tag/nzbhydra2-$tag_no_v-amd64-linux.zip"
unzip nzbhydra2-latest.zip -d nzbhydra2
sudo mkdir -p /opt/nzbhydra2
sudo cp -r nzbhydra2/* /opt/nzbhydra2

Set permissions:

sudo chown -R nzbhydra2:nzbhydra2 /opt/nzbhydra2/

Edit nzbhydra2.service in systemd:

vi systemd/nzbhydra2.service

Change the following to look like this:
User=nzbhydra2
Group=nzbhydra2
WorkingDirectory=/opt/nzbhydra2/ ExecStart=python3 /opt/nzbhydra2/nzbhydra2wrapperPy3.py --nobrowser

Install nzbhydra2 service:

sudo cp systemd/nzbhydra2.service /lib/systemd/system/

Enable the service on system startup:

sudo systemctl enable nzbhydra2

Start the service:

sudo systemctl start nzbhydra2

Check to see if the status is running:

sudo systemctl status nzbhydra2

To stop the service:

sudo systemctl stop nzbhydra2

To disable the auto startup:

sudo systemctl disable nzbhydra2