[systemd-devel] Starting a service before any networking

[Mark Rogers]

On Wed, 27 Sept 2023 at 09:39, Mantas Mikulėnas <grawity at gmail.com> wrote:

> It might be an issue with the kernel driver for your Ethernet interface,
> then (as setting the interface 'up/down' usually reinitializes the
> controller) – or possibly a physical issue with your cable or your switch,
> but it doesn't seem like the kind of issue that userspace configuration
> should be *able* to lead to in the first place. (...except maybe for EEE
> "power saving" stuff that might tip over a really marginal link.)
>

What doesn't make sense is that this had previously worked, although it's
possible that the network hardware has changed since it was previously
tested.


> (It's sort of like blaming a segfault crash on the user: if a program
> crashes, that's inherently a bug regardless of configuration. Here it's
> similar: if the Ethernet cable is really connected but the driver still
> reports "no carrier", that's either an interface issue or – if you see the
> same on multiple Pi's – perhaps a NIC driver issue, but it's not something
> that configuration ought to be *able* to do.)
>

OK, in that case if this persists I'll have to look at upgrading the whole
system, which I'm trying to avoid doing. But:


> Use the "drop-in" system (dhcpcd.service.d/*.conf), e.g. via `systemctl
> edit dhcpcd5`. Add a few ExecStartPre= commands in [Service] to have it
> "manually" bring the interface up, then down (possibly with a 'sleep .5'
> after each), and hopefully when dhcpcd brings it up the /second/ time it
> will work.
>

This has worked:
[Service]
ExecStartPre=ip addr
ExecStartPre=ip link set eth0 down
ExecStartPre=ip link set eth0 up
ExecStartPre=ip addr

(the "ip addr" calls are just to log the before/after state to journal).
It's booted in that state several times now successfully. I'll need to do
more testing yet but I am inclined to leave it at that (I hate workarounds
rather than actually fixing the issue but I suspect this is far as I'll
get).

Thank you (massively!) for your assistance on this.

-- 
Mark Rogers
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