On Wed, 14.07.10 19:42, Matthias Clasen (mclasen@xxxxxxxxxx) wrote:
>
> On Thu, 2010-07-15 at 01:29 +0200, Lennart Poettering wrote:
>
> [long comparsion elided...]
>
> > Or to explain this with a table, showing you what verbs most people
> > would probably use for four kinds (of the ten) of objects that are
> > managed by systemd:
> >
> > Services: Started | Stopped
> > Socket: Bound | Unbound
> > Devices: Plugged In | Plugged Out
> > Mounts: Mounted | Unmounted
> >
> > And we noticed that, and when we looked for more abstract terms that
> > could cover all three cases, we cam up with this:
> >
> > Units: Active | Inactive
> >
>
> Hey Lennart, instead of going all defensive here, I think it would be
> good to simply acknowledge that we are currently missing a 'friendly
> introduction to systemd' targeting sysadmins (or even regular users).
> The paragraph I cited above could be a nice start for a section in that
> document.
I kinda hoped that the Concepts part in the man page would actually
cover that already to enough detail:
"systemd provides a dependency system between various entities
called "units". Units encapsulate various objects that are relevant
for system boot-up and maintainance. The majority of units are
configured in unit configuration files, whose syntax and basic set
of options is described in systemd.unit(5), however some are created
automatically from other configuration or dynamically from system
state. Units may be active (meaning started, bound, plugged in,
... depending on the unit type), or inactive (meaning stopped,
unbound, unplugged, ...), as well as in the process of being
activated or deactivated, i.e. between the two states. The following
unit types are available:"
And then there's a list of the 10 types.
It's actually right the first paragraph after the list of options. Not
sure how I can make this any more obvious to find.
http://0pointer.de/public/systemd-man/systemd.html
> Well, I have to agree with notting that the sheer number of them is
> confusing, and if I look at how tiny they are, it makes me scratch my
> head even more: e.g. dbus.target:
>
> [Unit]
> Description=D-Bus
>
> Whats the point of all these empty targets ? Who are they good for ? My
> understanding so far was that targets collect groups of units for pure
> convenience, but this target does not collect anything...
Well, those targets are suggested hook points for units, i.e. they tend
to have special semantics:
http://0pointer.de/public/systemd-man/systemd.special.html
And those target files only exist to make clear that they exist, and so
that they get a pretty description assigned.
Note that "systemctl list-units" will only show active and referenced
units. No unreferenced ones. Hence I find it really useful that the
admin can browse through /lib/systemd/system and /etc/systemd/system to
see what units exist he could start or enable or whatever. If we would
not expose all units we have in the file system it would be much harder
to discover them.
Lennart
--
Lennart Poettering - Red Hat, Inc.
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