Licence change

[jrybar-rh]

Is your feature request related to a problem? Please describe.
According to automated licence check performed on lsof sources, the following licences are used: Sendmail, BSD, GPL and Henry Spencer/Purdue (the one containing "This software is not subject to any license of the American Telephone...").

The last one is GPL-ish-friendly and can probably be changed to GPL, especially when the licence used is archaic, obsoleted and "unsanitized". The lack of specifics of the "Purdue" -or whatever it's called- licence used may cause unease with FOSS software distribution, as the licences tend to be listed in package description among distros, and SPDX form equivalent.

[kurok]

Thanks for raising this. Here's an inventory of the licenses actually present in the current codebase:

1. Purdue/Abell License (primary, ~95% of files)
   This is the custom permissive license in COPYING. Good news: SPDX has since registered it with the identifier lsof (https://spdx.org/licenses/lsof.html), and ScanCode recognizes it as
   purdue-bsd (categorized as Permissive). So while it's not a "standard" license like MIT or BSD, it now has a proper SPDX identifier that package managers and distros can reference.

2. BSD-4-Clause (UC Berkeley, Paul Kranenburg)
   Found in borrowed code from OpenBSD/FreeBSD (netdb.h, portmap functions in print.c, pfsnode.h). This is the classic 4-clause BSD with the advertising clause. SPDX ID: BSD-4-Clause. It's
   compatible with the Purdue license, but the advertising clause is considered problematic by the FSF and some distros.

3. 0BSD/ISC-style (Tobias Nygren, 2022)
   Found in rnmt.c. This is a modern, maximally permissive license. There are no issues here.

4. SCO Proprietary headers
   Found in lib/dialects/uw/uw7/sys/fs/fifonode.h and namenode.h. These contain "UNPUBLISHED PROPRIETARY SOURCE CODE OF THE SANTA CRUZ OPERATION" headers. This is arguably the most concerning
   licensing issue in the repo, as proprietary headers in an open-source project create real distribution ambiguity.

Regarding the request to re-license under the GPL:

Relicensing is not straightforward for several reasons:

• The Purdue license is held by Purdue Research Foundation, not individual developers. Only Purdue (or their authorized representatives) can relicense that code.
• Apple Inc. holds copyright on the Darwin dialect portions and would need to consent.
• The BSD-4-Clause code from UC Berkeley and individual contributors has its own terms.
• GPL is a copyleft license, which is a fundamentally different licensing philosophy from the current permissive approach. Users currently embedding lsof in proprietary tools would lose
  that ability.

Practical suggestions:

1. The SPDX identifier lsof now exists - distros can use this directly in package metadata, solving the SPDX compliance concern.
2. A LICENSES/ directory with REUSE-compliant headers (per https://reuse.software) would help automated scanners correctly identify each file's license.
3. The SCO proprietary headers in lib/dialects/uw/uw7/ should be investigated - if UnixWare support is still relevant, these headers may need replacement or clarification.
4. If modernization is desired without changing license philosophy, BSD-2-Clause or MIT would be the closest modern equivalents to the Purdue license's intent, and would be easier to
   achieve than GPL (since they're permissive-to-permissive).