[systemd-devel] Starting service conditionally and retrying when failure

[Michael Chapman]

On Thu, 5 Oct 2017, Camilo Aguilar wrote:
> you need to active your service unit when your files show up by monitoring
> the path using an additional path unit:
> https://www.freedesktop.org/software/systemd/man/systemd.path.html

Anpother approach would be to have the unit get triggered by the device 
appearing in udev.

See the systemd.device(5) manpage for details. You just need a udev rule 
that adds a "systemd" TAG and a SYSTEMD_WANTS property to add a dependency 
upon the unit you wish to trigger.