Comment # 13 on bug 1198668 from Franck Bui

I don't think Type=exec is the correct fix here. If there's anything wrong with
purge-kernels.service ordering constraints then they should be fixed instead of
tweaking the type of the service itself.

You can start by inspecting the ordering constraints of purge-kernels.service
with `systemctl list-dependencies --before --all purge-kernels.service` for
example.

Or maybe add an additional "ExecStartPre=/usr/bin/sleep 60" in the service to
see if the problem is really an ordering issue. Maybe it's more related to slow
IOs or such. If that's the case, you might consider purging the kernel
regularly during runtime (with a timer unit and with limited IO resources for
the service) instead of doing that during the boot process.