[systemd-devel] Starting a service before any networking

[Mantas Mikulėnas]

On Wed, Sep 27, 2023 at 12:31 PM Mark Rogers <mark at more-solutions.co.uk>
wrote:

> On Wed, 27 Sept 2023 at 10:18, Mantas Mikulėnas <grawity at gmail.com> wrote:
>
>> So now I'm curious: if the first command you run is to bring the
>> interface *down*, then what exactly brought it up?
>>
>
> Good question. The reason for down/up was that this was working as a way
> to reset the connection after boot, so I just transferred that to the
> ExecStartPre.
>
> Looking at the "journalctl -u dhcpcd" output, this is what I see from my
> last boot:
> Feb 14 10:12:05 pi systemd[1]: Starting dhcpcd on all interfaces...
> Feb 14 10:12:05 pi ip[372]: 2: eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc
> noop state DOWN group default qlen 1000
> Feb 14 10:12:05 pi ip[372]:     link/ether b8:27:eb:0d:ee:bb brd
> ff:ff:ff:ff:ff:ff
> Feb 14 10:12:05 pi ip[383]: 2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP>
> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
> Feb 14 10:12:05 pi ip[383]:     link/ether b8:27:eb:0d:ee:bb brd
> ff:ff:ff:ff:ff:ff
> Feb 14 10:12:06 pi dhcpcd[385]: wlan0: starting wpa_supplicant
> Feb 14 10:12:36 pi dhcpcd[385]: timed out
> Feb 14 10:12:36 pi systemd[1]: Started dhcpcd on all interfaces.
> Feb 14 10:12:37 pi systemd[1]: Stopping dhcpcd on all interfaces...
> Feb 14 10:12:37 pi dhcpcd[519]: sending signal TERM to pid 466
> Feb 14 10:12:37 pi dhcpcd[519]: waiting for pid 466 to exit
> Feb 14 10:12:38 pi systemd[1]: dhcpcd.service: Succeeded.
> Feb 14 10:12:38 pi systemd[1]: Stopped dhcpcd on all interfaces.
> Feb 14 10:12:38 pi systemd[1]: Starting dhcpcd on all interfaces...
> Feb 14 10:12:38 pi ip[524]: 2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP>
> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
> Feb 14 10:12:38 pi ip[524]:     link/ether b8:27:eb:0d:ee:bb brd
> ff:ff:ff:ff:ff:ff
> Feb 14 10:12:38 pi ip[529]: 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu
> 1500 qdisc pfifo_fast state UP group default qlen 1000
> Feb 14 10:12:38 pi ip[529]:     link/ether b8:27:eb:0d:ee:bb brd
> ff:ff:ff:ff:ff:ff
> Feb 14 10:12:38 pi dhcpcd[530]: wlan0: starting wpa_supplicant
> Feb 14 10:12:49 pi dhcpcd[530]: Too few arguments.
> Feb 14 10:12:49 pi dhcpcd[530]: Too few arguments.
> Feb 14 10:12:49 pi systemd[1]: Started dhcpcd on all interfaces.
>
>  (I deleted the "ip addr" output from the interfaces other than eth0 for
> brevity.)
>
> The interesting thing is surely that dhcpcd is being started twice.
> Assuming that was always happening then that suggests dhcpcd was bringing
> the network up early (and failing but leaving it in a "stuck" state) and
> then again later (where it was unable to recover from the first failure,
> but now can)?
>

That's possible... but again, I don't see how it would get into this
"stuck" state in any other way but driver and/or hardware issues, as the
kernel driver is where the power-up sequence is done... dhcpcd (like 'ip
link set eth0 up') pretty much just tells the OS to power the NIC on, then
waits.

(My previous laptop had a Realtek Ethernet NIC that often wouldn't
recognize Ethernet link after suspend/resume until I removed it from the
PCI bus... took several kernel releases until they fixed that.)

-- 
Mantas Mikulėnas
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