-----Original Message-----
From: yocto@... <yocto@...> On
Behalf Of Bryan Evenson via lists.yoctoproject.org
Sent: Thursday, January 6, 2022 9:32 AM
To: yocto@...
Subject: [yocto] Problems switching from busybox-udhcpc to dhcpcd

I have a system that is based off core-image-minimal which uses sysvinit and
busybox-udhcpc. I'm trying to switch to dhcpcd because I want to get the
NTP server list from the local DHCP server; dhcpcd supports this feature and
busybox-udhcpc does not. I'm on the dunfell branch. I think I finally got
firmware upgrade to work cleanly (with opkg) but I'm having trouble
triggering dhcpcd. It doesn't work straight out of the box and I'm looking for
assistance in how to get dhcpcd started.

First, here are the recipe changes I made in my custom layer to install dhcpcd
onto my image and for it to get pulled in on firmware upgrade.
1. I added the following to my busybox_%.bbappend:

Do not install busybox-udcpcd, since we are using dhcpcd
RRECOMMENDS_${PN} = ""

2. I modified my busybox defconfig to unset all the udhcpc related
configuration features

3. I created a dhcpcd_%.bbappend with these contents:
# Set the package to conflict with busybox-udhcpc
RCONFLICTS_${PN} = "busybox-udhcpc"
RREPLACES_${PN} = "busybox-udhcpc"

# Add configuration settings to enable NTP configuration
PACKAGECONFIG += " \
ntp \
"
PACKAGECONFIG[ntp] = "--with-hook=ntp, , , ntp"

# Include the hook scripts on the system
EXTRA_OECONF += " \
--with-hooks \
"
4. In my init-ifupdown_%.bbappend:
a. I added dhcpcd to the RDEPENDS list
b. I added a script to start dhcpcd and installed it in the
${D}${sysconfdir}/network/if-up directory

5. Here is the if-up script (note: I only have one Ethernet port on this device
which will always be eth0):
#!/bin/sh

# Only do this for eth0 and not the loopback interface
if [ "$IFACE" == "eth0" ]; then
# Start the DHCP client
dhcpcd -4 -6 -f /etc/dhcpcd.conf "$IFACE"
fi


I think I'm close, but the dhcpcd never gets called when the Ethernet
interface starts up. As best I can tell from my debugging, I think $IFACE is
never set whenever my if-up script is called. I'm not sure why that is,
because I have a pre-up script that depends on $IFACE that has been working
for years for me.

First, I was having issue even directly calling dhcpcd from the command line with the line I had in my pre-up script. There have been some updates to the dhcpcd recipe in master that affects the file installation locations. I copied the dhcpcd recipe in master and put it in my custom layer. I could then call dhcpcd directly without issue.

Second, I needed to enable the CONFIG_FEATURE_IFUPDOWN_EXTERNAL_DHCP configuration parameter in busybox. The ifup and ifdown applets from Busybox were not attempted to call dhcpcd without this set. Once I got both of these fixes in place, I found out that I don't need the if-up script I had created. Everything is running fine now.

Has anyone else made this transition that can offer some more support? Are
there some examples floating around on how to start dhcpcd on ifup that I
am missing?

Thanks,
Bryan Evenson

Bryan Evenson