On Wed, 27 Sept 2023 at 09:39, Mantas Mikulėnas <grawity@xxxxxxxxx> 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
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
