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fix: explicitly configure dhcp in ip= kernel command line#245

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enr0n:fix-ip-kernel-opt
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fix: explicitly configure dhcp in ip= kernel command line#245
enr0n wants to merge 1 commit into
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enr0n:fix-ip-kernel-opt

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@enr0n

@enr0n enr0n commented May 12, 2026

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The ip= kernel command line option is implemented slightly differently across dracut, initramfs-tools, systemd-network-generator, etc.

Dracut now lets systemd-network-generator handle ip= parsing, and systemd-network-generator requires that the DHCP type is set when the interface name is. E.g.,

ip=::::bibarel:BOOTIF:dhcp BOOTIF=01-ec:b1:d7:7f:2a:6c

is valid but

ip=::::bibarel:BOOTIF BOOTIF=01-ec:b1:d7:7f:2a:6c

is not. Ubuntu currently carries a downstream patch to allow for easier migration from initramfs-tools, but going forward the DHCP type should be set explicitly. Hence, set it to "dhcp", which is the behavior when unspecified in initramfs-tools.

Related: LP#2141588

@enr0n enr0n requested a review from a team May 12, 2026 08:27
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enr0n commented May 12, 2026

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/cc @bdrung for awareness

@r00ta r00ta left a comment

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@enr0n is this backwards compatible? What if the user is deploying another previous version of Ubuntu?

@enr0n

enr0n commented May 14, 2026

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@enr0n is this backwards compatible? What if the user is deploying another previous version of Ubuntu?

I believe so, but it has been a little while since I checked (and I sometimes confuse the various implementations), so I will double check.

@enr0n

enr0n commented Jun 10, 2026

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@enr0n is this backwards compatible? What if the user is deploying another previous version of Ubuntu?

Sorry for the delay, I was OOO for a bit. Yes, this is backwards compatible. See e.g. this test case for initramfs-tools: https://git.launchpad.net/ubuntu/+source/initramfs-tools/tree/debian/tests/qemu-net#n81.

I.e. it is supported to explicitly configure "dhcp" or so in that field.

@enr0n enr0n force-pushed the fix-ip-kernel-opt branch from e58f2c7 to ad08319 Compare June 10, 2026 15:28
@enr0n enr0n force-pushed the fix-ip-kernel-opt branch from ad08319 to ea4f250 Compare July 1, 2026 19:56
The ip= kernel command line option is implemented slightly differently
across dracut, initramfs-tools, systemd-network-generator, etc.

Dracut now lets systemd-network-generator handle ip= parsing, and
systemd-network-generator requires that the DHCP type is set when
the interface name is. E.g.,

 ip=::::bibarel:BOOTIF:dhcp BOOTIF=01-ec:b1:d7:7f:2a:6c

is valid but

 ip=::::bibarel:BOOTIF BOOTIF=01-ec:b1:d7:7f:2a:6c

is not. Ubuntu currently carries a downstream patch to allow for easier
migration from initramfs-tools, but going forward the DHCP type should
be set explicitly. Hence, set it to "dhcp", which is the behavior when
unspecified in initramfs-tools.

Related: LP: #2141588
@enr0n enr0n force-pushed the fix-ip-kernel-opt branch from ea4f250 to 15a960a Compare July 1, 2026 19:58
@enr0n

enr0n commented Jul 1, 2026

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@r00ta gentle ping. I pushed with my canonical email to fix the CLA check.

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2 participants