[systemd-devel] systemd: questions about dbus dependency service

[Lennart Poettering]

On Di, 28.11.23 22:48, Pintu Agarwal (pintu.ping at gmail.com) wrote:

> Hi,
>
> I need some clarification about systemd services that are dependent on dbus
> service.
>
> We have a service that depends on dbus.service, so our service has to be
> started after dbus.socket and dbus.service.

It's usually a good idea to not wait for dbus.sevice. Waiting for
dbus.socket is sufficient, it makes sure clients can connect to D-Bus
(even if dbus needs to finish starting up to respond to it). This will
increase parallelization during boot.

> But dbus.service comes after local-fs.target and sysinit.target.
> However, our service needs to be started very early on boot-up, maybe
> within local-fs target itself, otherwise it is causing regression in our
> boot KPI.

dbus is not a suitable IPC for early boot services, unless you speak
the dbus protocol directly between client and service, without
involving the broker. But that's messy.

systemd's PID 1 does this (i.e. dbus without a broker), because it
must be accessible early on, but I hate that code, and I'd rather kill
it. In new code that must run in early boot we usually use a different
IPC (varlink), that does not involve any broker, and thus always works.

Lennart

--
Lennart Poettering, Berlin