systemd service file for running a transmission-daemon through OpenVPN

README.md

What is still missing

• mullvad-up.sh as called from openvpn.conf would be unnecessary if openvpn would fork after setting up the tun interface, for then its contents could be realized with a few systemd ExecStartPost-directives.
• Some means of automatically detecting and stopping/reconnecting a broken connection would be nice.
• Due to libcurl being buggy, transmission-daemon leaks DNS requests. I don't mind, if you do, consider using a couple of iptables rules to route any packets coming from transmission's UID through a special routing table.

mullvad-up.sh

#!/usr/bin/env bash
# /etc/openvpn/mullvad-up.sh

#Routing table setup
/usr/sbin/ip route flush table transmission
/usr/sbin/ip route add 10.8.0.0/24 dev "$dev" src "$ifconfig_local" table transmission
/usr/sbin/ip route add default via "$ifconfig_remote" table transmission

#Routing rule setup
/usr/sbin/ip rule del lookup transmission
/usr/sbin/ip rule del lookup transmission
/usr/sbin/ip rule add to "$ifconfig_local" lookup transmission
/usr/sbin/ip rule add from "$ifconfig_local" lookup transmission

#Firewall setup
#iptables -A OUTPUT -o %i -m owner --uid-owner transmission -j ACCEPT
#iptables -A OUTPUT -o lo -m owner --uid-owner transmission -j ACCEPT
#iptables -A OUTPUT -m owner --uid-owner transmission -j DROP

systemctl start transmission-vpn@$ifconfig_local

mullvad-vpn.service

# /etc/systemd/system/mullvad-vpn.service
[Unit]
Description=OpenVPN connection to Mullvad
After=network.target
#StopWhenUnneeded=true
 
[Service]
Type=forking
ExecStart=/usr/sbin/openvpn --cd /etc/openvpn --config /etc/openvpn/mullvad.conf --daemon mullvad-vpn --writepid /var/run/openvpn-mullvad.pid
PIDFile=/var/run/openvpn-mullvad.pid
ExecStopPost=/usr/sbin/ip rule del lookup transmission
ExecStopPost=/usr/sbin/ip rule del lookup transmission
ExecStopPost=/usr/sbin/ip route flush table transmission
 
[Install]
WantedBy=network.target

mullvad.conf

# /etc/openvpn/mullvad.conf
# Notice to Mullvad customers:
# 
# Apart from openvpn, you also need to install the
# package "resolvconf", available via apt, e.g.
#
# For those of you behind very restrictive firewalls,
# you can use our tunnels on tcp port 443, as well as
# on udp port 53.
client

dev tun

user nobody
group nobody
 
proto udp
#proto tcp

#remote openvpn.mullvad.net 1194
#remote openvpn.mullvad.net 443
#remote openvpn.mullvad.net 53
remote se.mullvad.net # Servers in Sweden
#remote nl.mullvad.net # Servers in the Netherlands

# Keep trying indefinitely to resolve the
# host name of the OpenVPN server.  Very useful
# on machines which are not permanently connected
# to the internet such as laptops.
resolv-retry infinite
  
# Most clients don't need to bind to
# a specific local port number.
nobind

# Try to preserve some state across restarts.
persist-key
persist-tun

# Enable compression on the VPN link.
comp-lzo

# Set log file verbosity.
verb 3
 
remote-cert-tls server
 
ping-restart 20
 
# Allow calling of built-in executables and user-defined scripts.
script-security 2
 
up /etc/openvpn/mullvad-up.sh
 
# Parses DHCP options from openvpn to update resolv.conf
#up /etc/openvpn/update-resolv-conf
#down /etc/openvpn/update-resolv-conf
 
ping 10
 
ca master.mullvad.net.crt
cert mullvad.crt
key mullvad.key

route-nopull

rt_tables

# /etc/iproute2/rt_tables
# Adapt for your needs
255     local
254     main
253     default
23      transmission
0       unspec

transmission-vpn@.service

# /etc/systemd/system/transmission-vpn@.service
[Unit]
Description=Transmission BitTorrent Daemon over Mulvard Openvpn
Requires=mullvad-vpn.service

[Service]
Type=simple
User=transmission
WorkingDirectory=/mnt/storage/torrent
ExecStart=/usr/bin/transmission-daemon -c torrents --foreground -ep -gsr 2.0 --incomplete-dir incomplete --no-portmap --bind-address-ipv4 %i --bind-address-ipv6 ::1 --dht --rpc-bind-address 127.0.0.1 --utp --download-dir download --log-error

[Install]