Source files for libnml lack standard Debian or SPDX copyright headers. Also obsolete version of LGPL used.

Source files for both the core linuxcnc & libmnl are forked and munged from a NIST project known as the Enhanced Machine Control (EMC). The source code for this is public domain. One can NOT take PD code, claim copyright, and then slap an arbitrary license on it.

At best, renders the license unenforceable in many jurisdictions, or illegal in some.

Kindly refer to Debian Legal

[Adam Ant]

Can you be more specific?  I do not understand what you mean by
"standard Debian or SPDX copyright headers", and fail to understand
how using old LGPL versions would be a problem.  Perhaps you can
prepare a patch with what you believe are more accurate copyright
information?  It would make it easier to understand exactly what
you are talking about.

I am unaware of any jurisdictions where publishing work derived from
public domain works would make it illegal to distribute.  Which
jurisdictions do you have in mind here?

Note, I agree that relicensing public domain works might be hard to
enforce copyright on the public domain code if the same code is
published both "alone" as public domain and as part of some non-public
domain code, as it would be hard to prove which version was the base of
such use, but that do not seem to be a relevant issue for distributing
LinuxCNC.

Are you refering to specific existing posts on Debian Legal, or
suggesting we bring up some topic on the list ourself?  If the former,
can you point to specific posts on lists.debian.org?

Control: severity -1 normal

(Standard disclaimer: IANAL.)

This is nice to have, but it is not a requirement.

 Also obsolete version of LGPL used.

Where is this a problem? All LGPL variants a DFSG approved. The license is upstream's *choice*,
code, claim copyright, and then slap an arbitrary license on it.
"Software placed in the public domain has all the freedoms required by the DFSG, and is free software."

Where would be distributing PD illegal?

You've got an answer from Andrew actually. (which you should have considered as input, when filing this bug.
In fact, you just filed this bug as if the reponse never happened. That raises some concerns on your behaviour.)

Let me quote the relevant part for the bug: (https://lists.debian.org/debian-legal/2022/12/msg00001.html)

And according to a comment in d/copyright, this is exactly what happened.

(As Andy pointed out, this is not legal advice. Read the whole thread)

I don't see a (RC) bug for Debian here, sorry.
Downgrading it, I'll leave it up to the maintainers to close it, so that they can also double
check whether I've missed something when looking at this bug)

Yes, Public Domain is indeed "free software" and you can incorporate it in a larger project (either proprietary or FOSS). But what you can not do is to claim copyright over that code or re-license it.

By slapping a copyright notice on a file, you are basically claiming "I wrote this". Give the original authors due credit and mark the files as Public Domain source.

LinuxCNC are in the EMC project, it is actually based on EMC2. The
EMC2 copyright statement states:

"Notice:  Most of EMC2 is covered by the GNU General Public
License.  Some portions are covered by the GNU Lesser
General Public License (mostly interface definitions).
Both licenses are included in their entirety below.

Much of EMC2 is derived from EMC1, a work of Fred Proctor, Tom
Kramer, Will Shackleford, and others.  That work was originally
released into the public domain.  It was used as the basis of
EMC2, but received extensive modifications.  EMC2 is NOT public
domain.  Anyone wishing to use the public domain code in a way
that is not compatible with the (L)GPL must locate the original
EMC1 code - they may NOT use EMC2."

Reviewing  source files for libnml they state:
License: GPL Version 2

We should be very careful arbitrating over decades old code as the
original context can easily be lost.

Rod Webster