[systemd-devel] "bad" status for genersated target; why?

[Andrei Borzenkov]

On Wed, May 15, 2019 at 9:01 AM Ulrich Windl
<Ulrich.Windl at rz.uni-regensburg.de> wrote:
>
> >>> Andrei Borzenkov <arvidjaar at gmail.com> schrieb am 14.05.2019 um 20:21 in
> Nachricht <c39c1270-41bf-dd7a-ed39-11c148f336a9 at gmail.com>:
> > 14.05.2019 16:39, Ulrich Windl пишет:
> >> Hi!
> >>
> >> Developing my first systemd service I have some problems I don't
> understand:
> >> After installation, I get this status:
> >> # systemctl status iotwatch.target          ● iotwatch.target - iotwatch
> I/O
> >> performance monitor
> >>    Loaded: loaded (/run/systemd/generator.late/iotwatch.target; bad;
> vendor
> >> preset: disabled)
> >>    Active: inactive (dead)
> >>      Docs: man:iotwatch at .service(8)
> >>            man:iotwatch-generator(8)
> >>
> >> Why "bad"?
> >
> > Again - this has improved in current version which now tells you that
> > unit is generated.
>
> So there's nothing wrong with the unit?
>
> >
> >> # ll /run/systemd/generator.late/iotwatch.target
> >> -rw-r--r-- 1 root root 281 May 14 15:24
> >> /run/systemd/generator.late/iotwatch.target
> >> # systemctl is-enabled iotwatch.target
> >> Failed to get unit file state for iotwatch.target: No such file or
> directory
> >>
> >> Here we are again: Where should the file be?
> >> Aren't targets allowed to be generated?
> >>
> >
> > Targets are allowed to be generated but generated units cannot be
> > enabled/disabled. The rationale probably is that if you create unit file
> > you can just as well create symlink to this unit file. Also "systemctl
>
> I think "Generated iotwatch.target cannot have a state" would be a much
> improved error message then.

Define "state".

> So again there's nothing wrong with the unit
> file?
>
> > dameon-reload" removes and re-creates all generated units, so any
> > symlink to such unit outside of generated subdirectories potentially
> > becomes invalid.
>
> I think all the symlink stuff should be an implementation detail that
> shouldn't be part of the user interface; instead there should be some
> higher-level commands to maipulate these.
>

It is exactly the opposite - symlinks are *the* official documented
method to configure unit dependencies; "systemctl enable" is just
convenience layer on top of it.

> >
> > Documentation could be better indeed.
>
> Finally: If a generated unit cannot be enabled or disabled, isn't the
> "vendor-preset: disabled" the wrong choice:

Neither is it printed in current systemd version.

> I specified nothing, and the logic
> should be: If a generator created a unit it should be enabled; otherwise sich a
> unit shouldn't be enabled.
>

You misinterpret "enabled" and "disabled" basing on their English
meaning. Unit is "enabled" if links specified in [Install] sections
are present. Nothing more nothing less. You apparently assume
"enabled" means something different.

Generators run immediately before systemd computes initial
transaction; there is no point in time when user could perform
"systemctl enable" on them - it is already too late, system is already
booted using whatever configuration (including generated units) was
present. So any required links really have to be created together with
generated unit itself.

> I couldn't find the relevant manual page that discusses this topic...
>

Yes, the fact that generated units apparently cannot be
enabled/disabled using systemctl is not documented anywhere. Still
current systemd gives quite precise error message when you are trying
to do it. But documentation could certainly be improved.