[systemd-devel] [question] networkd: Any support for hooks?

[Tom Gundersen]

On Fri, Oct 10, 2014 at 11:40 PM, Dale R. Worley <worley at alum.mit.edu> wrote:
>> From: Tom Gundersen <teg at jklm.no>
>
>> What we do, however, is to expose the configuration state using the
>> sd-network C API, which external programs can watch and react on (see
>> how timesyncd and resolved currently works).
>
> In a situation where one wants to do what a "hook" does, having a
> separate daemon program that watches for an event and then invokes the
> hook when the event happens is not a good solution -- it replaces the
> hook with an entire daemon.
>
> I am not experienced, but from what little I know about systemd, the
> "natural" way would seem to be to write a new unit file with the
> appropriate dependencies.  The event that should call the hook is when
> some unit finishes starting, and then the new unit would then be
> started.

Well, in some cases you can do this. For instance, we have the
network-online.target which gets triggered for some notion of
"online".

However, if you want more fine-grained control than any of the
existing units give you, you probably have to hook into
rtnl/networkd/udev events to get precisely what you want. For any
non-trivial setup, this is likely what you want anyway as you probably
need to react to the network coming and going (and not only when it
first gets configured). For a few examples of how this hook-up can be
done, see networkd-wait-online, timesyncd and resolved in the systemd
repo.

Cheers,

Tom