Install qBittorrent-nox:

sudo apt install -y qbittorrent-nox

After installation, we can check qBittorrent-nox version:

qbittorrent-nox --version

Run qBittorrent-nox as a service

In order to run qBittorrent-nox as a service we need to configure systemd. Create a systemd unit file:

sudo nano /etc/systemd/system/qbittorrent-nox.service

Add following content to the file:
########################
[Unit]
Description=qBittorrent client
After=network.target

[Service]
ExecStart=/usr/bin/qbittorrent-nox --webui-port=8080
Restart=always

[Install]
WantedBy=multi-user.target

##############################
You can change web interface port if you want.

Start qBittorrent-nox service:

sudo service qbittorrent-nox start

You can run the following command to make sure that qBittorrent-nox service is running:

sudo service qbittorrent-nox status

Also you can stop or restart the service:

sudo service qbittorrent-nox stop
sudo service qbittorrent-nox restart

To enable qBittorrent-nox to start on boot, run the following command:

sudo systemctl enable qbittorrent-nox

Testing qBittorrent-nox

Open a browser and enter URL address http://<IP_ADDRESS>:8080, where <IP_ADDRESS> is IP address of your machine. You can log in to the web UI with the default username (admin) and password (adminadmin).
#############################
If you want to completely remove the qBittorrent-nox, stop the service and remove a systemd unit file.

sudo service qbittorrent-nox stop
sudo systemctl disable qbittorrent-nox
sudo rm -rf /etc/systemd/system/qbittorrent-nox.service
sudo systemctl daemon-reload
sudo systemctl reset-failed

Remove qBittorrent-nox:

sudo apt purge --autoremove -y qbittorrent-nox

You can also remove the qBittorrent configuration, cache, and other related directories:

sudo rm -rf /.config/qBittorrent
sudo rm -rf /.local/share/qBittorrent
sudo rm -rf /.cache/qBittorrent
rm -rf ~/.config/qBittorrent
rm -rf ~/.local/share/qBittorrent
rm -rf ~/.cache/qBittorrent