So I've been looking at the openvpn configuration on my Debian 9 based server and found something that I cannot explain in the systemd unit files for the openvpn daemon. The daemon itself is starting and working without problems, but I can't figure out why... Let me explain :)
So I've got openvpn installed and have a proper configuration in the /etc/openvpn/server.conf file. Nothing wrong so far.
However, apparently two systemd units are running for openvpn, namely openvpn.service and email@example.com. The latter seems to be the one that actually accepts the incomming vpn connections and such, the former one does't appear to do much at all. It apparently just runs to start the latter, I suppose...
Checking the /etc/systemd/system/multi-user.target.wants/ directory for openvpn related files shows only the openvpn.service file, which of source is a symlink to a similar named file in /lib/systemd/system. The contents of this file is:
# This service is actually a systemd target, # but we are using a service since targets cannot be reloaded. [Unit] Description=OpenVPN service After=network.target [Service] Type=oneshot RemainAfterExit=yes ExecStart=/bin/true ExecReload=/bin/true WorkingDirectory=/etc/openvpn [Install] WantedBy=multi-user.target
Ok, cool. So this only runs /bin/true. Then what exactly starts the openvpn@server daemon? I know that the unit file for this is /lib/systemd/openvpn@.service but I cannot find any clue whatsoever on my system to what exactly runs this unit file. (I was expecting to find a symlink for this under /etc/systemd/system somwhere, but there isn't.) The content of this file is:
[Unit] Description=OpenVPN connection to %i PartOf=openvpn.service ReloadPropagatedFrom=openvpn.service Before=systemd-user-sessions.service Documentation=man:openvpn(8) Documentation=https://community.openvpn.net/openvpn/wiki/Openvpn23ManPage Documentation=https://community.openvpn.net/openvpn/wiki/HOWTO [Service] PrivateTmp=true KillMode=mixed Type=forking ExecStart=/usr/sbin/openvpn --daemon ovpn-%i --status /run/openvpn/%i.status 10 --cd /etc/openvpn --config /etc/openvpn/%i.conf --writepid /run/openvpn/%i.pid PIDFile=/run/openvpn/%i.pid ExecReload=/bin/kill -HUP $MAINPID WorkingDirectory=/etc/openvpn ProtectSystem=yes CapabilityBoundingSet=CAP_IPC_LOCK CAP_NET_ADMIN CAP_NET_BIND_SERVICE CAP_NET_RAW CAP_SETGID CAP_SETUID CAP_SYS_CHROOT CAP_DAC_READ_SEARCH CAP_AUDIT_WRITE LimitNPROC=10 DeviceAllow=/dev/null rw DeviceAllow=/dev/net/tun rw [Install] WantedBy=multi-user.target
So this unit file has a lot more substance than the openvpn.service file. But what kicks it off? I've noticed the PartOf=openvpn.service part in the above file, but looking up the meaning of this in the man pages hasn't made me much wiser.
I'll continue searching because I just want to know what makes this thing tick!
If any one you have any clue about how this specific unit file is run, or what starts it, please let me know :)