…in case you don’t want to spend too much time and have a nice torrent client with web interface installed on your Raspberry Pi, qBittorrent is probably a good option (even full of settings).

Of course, we need to install the package (we install the one with NO GUI, only web interface):

apt install qbittorrent-nox

We also want to create a user with minimum privileges to run this software.
We are going to create a user called torrent part of a new group called torrent as well, within a home directory in /var/torrent
After that, we will add our own user (e.g. user1 to the torrent group, in order to allow you to access the downloaded files.
We are also creating a downloads folder, setting the right permissions.

adduser --system --group --home /var/torrent torrent
adduser user1 torrent
mkdir -p /var/torrent/downloads
chown torrent:torrent /var/torrent/downloads
chmod 770 /var/torrent/downloads

Now we’re going to create a new systemd service file: /etc/systemd/system/qbittorrent-nox.service

[Unit]
Description=BitTorrent Client
After=network.target

[Service]
Type=forking
User=torrent
Group=torrent
UMask=002
ExecStart=/usr/bin/qbittorrent-nox -d --webui-port=8080
Restart=on-failure

[Install]
WantedBy=multi-user.target

Enable and start the service:

systemctl enable qbittorrent-nox
systemctl start qbittorrent-nox

You should now be able to connect to your raspberry pi’s IP, on port 8080.

You will be asked to login.
Note: default username is admin, and the password is adminadmin.
Once logged in, under Settings > WebUI, you can whitelist your local network (e.g. 192.168.10.0/8) to skip authentication.

…and yes, that’s it

I told you it was a quick one!

Enjoy!