I've finally found it. I was at the point where I had two (different hardware) embedded systems. Both with the *same* kernel and mounting the *same* root NFS filesystem. Even exchanging the IP-Addresses didn't change the behaviour, the Orange-Pi issues a DHCPDECLINE, the other system works fine.
The cause is that on the non-working system the root NFS was mounted read-only. Note that I mount a (writeable) tmpfs on /var/lib/dhcp where apparently dhclient puts its leases. So there is another undocumented location that apparently needs to be writeable. It would be *very* nice to document which directories dhclient needs to be writeable and under what circumstances it issues a DHCPDECLINE. Note that the DHCPDECLINE has an optional message where the client could tell the server the reason for the decline. It's left empty, I've checked with tcpdump. For the record: The message "RTNETLINK answers: File exists" was a red herring: It is always issued, also in the successful case. I think we can close this issue unless you want to keep it open as a reminder that the causes for DHCPDECLINE should be documented. Oh and dhclient probably should not retry when it detects that something is unwriteable and effectively perform a denial-of-service attack on the dhcp server. Instead it should terminate with an error message that is clearly visible (not just in a log that may not exist at that stage of booting). Working example: root@sun7i:~# mount -oremount,rw 10.23.5.5:/data/project/project/rootfs/A20-OLinuXino_MICRO root@sun7i:~# ifup eth0 Internet Systems Consortium DHCP Client 4.4.1 Copyright 2004-2018 Internet Systems Consortium. All rights reserved. For info, please visit https://www.isc.org/software/dhcp/ Listening on LPF/eth0/02:42:b3:f0:2d:3e Sending on LPF/eth0/02:42:b3:f0:2d:3e Sending on Socket/fallback Created duid "\000\001\000\001#\367\373\266\002B\263\360->". DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 3 DHCPOFFER of 10.23.5.173 from 10.23.5.254 DHCPREQUEST for 10.23.5.173 on eth0 to 255.255.255.255 port 67 DHCPACK of 10.23.5.173 from 10.23.5.254 RTNETLINK answers: File exists bound to 10.23.5.173 -- renewal in 1396 seconds. root@sun7i:~# Ralf -- Dr. Ralf Schlatterbeck Tel: +43/2243/26465-16 Open Source Consulting www: www.runtux.com Reichergasse 131, A-3411 Weidling email: off...@runtux.com
