[systemd question] How does the rtorrent service start as the rtorrent user?

[kartikynwa]

This is what /etc/systemd/system/rtorrent.service looks like:

[Unit]
Description=rTorrent (DietPi)
Wants=network-online.target
After=network-online.target remote-fs.target

[Service]
User=rtorrent
ExecStart=/usr/bin/rtorrent

[Install]
WantedBy=multi-user.target

I can't see how it knows that it has to start as the rtorrent user. Yet it does. What am I missing here? I don't know systemd well.

[kartikynwa]

OMG I am an idiot. It's right there on line 7.

[MichaIng]

The official docs are not bad to get an overview and details about available systemd directives: https://www.freedesktop.org/software/systemd/man/latest/systemd.exec.html#User=

It is split a bit annoyingly (IMO) across multiple pages, like systemd.unit for very general directives and mostly (but not only) those of the [Unit] section, the systemd.exec page I liked above for directives which have a direct effect on Exec* directives (like with which user/group it is executed), but without Exec* directives themselves, and the systemd.service page with other directives from the [Service] section, with a more indirect effect on how things are started, and the `Exec*´ directives themselves. Cycling through those 3 pages should answer most questions about how to achieve things and which directives/value means what.

And in case you plan to change the user, at best do not edit the service files themselves, but create a drop-in config, to override individual values. E.g.:

mkdir /etc/systemd/system/rtorrent.service.d
cat << '_EOF_' > /etc/systemd/system/rtorrent.service.d/myuser.conf
[Service]
User=myuser
_EOF_
systemctl daemon-reload
systemctl restart rtorrent