Olivier Brunel:
With instanced services, it means when you enable such a service you
add/specify an instance name. So e.g. the servicedir is "getty@" but
you enable "getty@tty2" -- which just means the servicedir getty@ is
copied under a different name in the scandir.
The intent being that to enable another getty, you just enable
getty@tty3 and that's it. [...]
nosh has much the same. Look at the nosh-bundles package and you'll
find a set of ttylogin@ttyv* service bundles, for starters. There are
plenty of others, from mdmfs@-tmp to populate@var, with a whole bunch of
kmod@* service bundles along the way.
The convert-systemd-units tool can convert templatized systemd units.
The configuration import subsystem instantiates multiple instances of a
generic service for per-user dbus daemons, Warden jails, webcamd
services, rfcomm_pppd services, static_arp, static_ndp, pefs, geli,
geom, fsck, ZFS mounts, and so forth. If you want to know where the
idea of instances of a generic can be used, look in the nosh-bundles
package.
There's no instantiation mechanism in the service bundles themselves.
Everything is pre-instantiated at conversion/creation time. That's when
all of the template parameter substitution happens, not at runtime.
This is not to say that it's impossible to share service/ directories
amongst service bundles. It's quite possible, and part of the design.
It's just not used for instantiation; because in that case the service/
directories differ in their run/start/stop/restart programs, because of
the instance names.
