Poul-Henning Kamp

Poul-Henning Kamp
Kamp in 2013
Other namephk
OccupationProgrammer
EmployerSelf-employed
Known forvarious contributions to FreeBSD and Vinyl Cache

Poul-Henning Kamp (Danish: [ˈpʰʌwl ˈhene̝ŋ ˈkʰɑmˀp]) is a Danish computer software developer known for work on various projects including FreeBSD and Vinyl Cache. He currently resides in Slagelse, Denmark.

Involvement in the FreeBSD project

Poul-Henning Kamp has been committing to the FreeBSD project for most of its duration. He is responsible for the widely used MD5crypt implementation of the MD5-based password hash algorithm, a vast quantity of systems code including the FreeBSD GEOM storage layer, GBDE cryptographic storage transform, part of the UFS2 file system implementation, FreeBSD Jails, the phkmalloc implementation of the malloc library call, and the FreeBSD and NTP timecounters code, and the nanokernel interface with David Mills.

Vinyl Cache

He is the lead architect and developer for the open source Vinyl Cache project (formerly Varnish Cache), an HTTP accelerator.

In 2006, Kamp had a dispute with electronics manufacturer D-Link in which he claimed they were committing NTP vandalism by embedding the IP address of his NTP servers in their routers. The dispute was resolved in April 2006.

Beerware

Beerware
AuthorPoul-Henning Kamp
Latest version42
PublisherYes
Published1998
Debian FSG compatibleYes
FSF approvedYes (see "informal license" section)
OSI approvedNo
GPL compatibleYes
CopyleftNo
Linking from code with a different licenseYes
Websitepeople.freebsd.org/~phk/ Edit this on Wikidata

Beerware is a tongue-in-cheek software license with permissive terms, which grants the user the rights to do anything with the source code, including editing and distributing, so long as the license notice is preserved. The informal wording has been criticized as creating substantial legal ambiguity for its users.

Should the user of the code consider the software useful, they are encouraged to buy the author a beer "in return" if they ever meet. The Humanitarian-FOSS project at Trinity College recognized the "version 42" beerware license variant as an extremely permissive "copyright only" and GPL-compatible license. According to the Free Software Foundation, the license would be classified as an "informal" free, non-copyleft and GPL-compatible license, however more detailed licenses are recommended. As of October 2025, Beerware hasn't been approved by the Open Source Initiative (OSI).

Kamp states his preference of his Beerware license over other licenses, such as BSD and GPL, the latter of which he has described as a "joke". The full text of Kamp's license is:

/*
 * ----------------------------------------------------------------------------
 * "THE BEER-WARE LICENSE" (Revision 42):
 * <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
 * can do whatever you want with this stuff. If we meet some day, and you think
 * this stuff is worth it, you can buy me a beer in return Poul-Henning Kamp
 * ----------------------------------------------------------------------------
 */

Bike shed discussion

FOSDEM 2014: "NSA operation ORCHESTRA Annual Status Report" by Kamp

A post by Kamp on the FreeBSD mailing lists is responsible for the popularization of the term bike shed discussion, and the derived term bikeshedding, to describe Parkinson's law of triviality in open source projects – when the amount of discussion that a subject receives is inversely proportional to its importance.

Publications

Poul-Henning Kamp has published a substantial number of articles over the years in publications like Communications of the ACM and ACM Queue mostly on the topics of computing and time keeping. A selection of publications:

See also

Notes

  1. ↑ According to the Wayback Machine, the earliest revision of Poul-Henning Kamp's website containing the license is 1998. It is unknown whether this was indeed the first year of the license's publication.

References

  1. ↑ "List of FreeBSD committers on FreeBSD.org".
  2. ↑ "PHKs Bikeshed, MD5crypt Is No longer safe". Retrieved 13 March 2013.
  3. ↑ Norris, Jeff (2004). "Mission-Critical Development with Open Source Software: Lessons Learned". IEEE Software. 21 (1). IEEE Computer Society: 42–49. doi:10.1109/MS.2004.1259211. S2CID 8324900.
  4. ↑ Kamp, Poul-Henning (2002). "Timecounters: Efficient and precise timekeeping in SMP kernels" (PDF). Proceedings of the BSDCon Europe. EuroBSDcon. Netherlands. p. 10.
  5. ↑ Mills, David; Kamp, Poul-Henning (2000). "The nanokernel". Proceedings of the 32th Annual Precise Time and Time Interval Systems and Applications Meeting. Precise Time and Time Interval Systems and Applications. Reston, Virginia, USA. pp. 423–430.
  6. ↑ "On Vinyl Cache and Varnish Cache - Vinyl Cache". vinyl-cache.org. Retrieved 2026-05-31.
  7. ↑ "D-Link Firmware Abuses Open NTP Servers".
  8. ↑ Kamp, Poul-Henning. "Open Letter to D-Link about their NTP vandalism". Archived from the original on 2006-04-08.
  9. ↑ Kamp, Poul-Henning (2006-04-27). "2006-04-27 Update – Open Letter to D-Link about their NTP vandalism". people.freebsd.org. Retrieved 2017-03-01.
  10. 1 2 Kamp, Poul-Henning (2004-10-24). "Poul-Henning Kamp". Archived from the original on 21 April 2006. Retrieved 2006-04-24.
  11. 1 2 3 4 5 "Various Licenses and Comments about Them § Informal license". www.gnu.org. Free Software Foundation. 2016-01-05. Retrieved 2016-01-05.
  12. 1 2 "Beerware License". Humanitarian-FOSS. Archived from the original on 2016-03-22. Retrieved 2015-04-20. The license is compatible with proprietary licenses and the GNU GPL, as code under this license has no restrictions whatsoever.
  13. ↑ I think the GNU license is a joke, it fights the capitalism it so much is against with their own tools, and no company is ever going to risk any kind of proximity to so many so vague statements assembled in a license.
  14. ↑ "A bike shed (any colour will do) on greener grass...", freebsd-hackers mailing list, 1999
  15. ↑ "Why Should I Care What Color the Bikeshed Is?". bikeshed.org. Retrieved 11 August 2020.

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