To sum up:
- The user instance stuff with
--user
is intended to be used on a desktop computer. Syncthing starts when you log in to gnome or something; and it stops when you log out. - The system instance stuff is useful for a server. Syncthing then starts during the normal bootup sequence and stays running. To be able to specify the user, there is the templating stuff with
@
, e.g.:systemctl start syncthing@hans.service
. - The user units are located in
/usr/lib/systemd/user/
and can be overwritten in/etc/systemd/user/
and~/.config/systemd/user/
. - The system units are located in
/usr/lib/systemd/system/
and can be overwritten in/etc/systemd/system/
.
So, when you mix them up by accident, strange things happen.
Note: The paths are valid for arch linux and fedora and are documented in the systemd manpages. Debian (as usual) does its own thing.