For some years now I have included the “X-Clacks-Overhead” header in trivia’s lighttpd.conf as a tribute to the late great Sir Terry Pratchett. I am a huge fan of Pratchett’s Discworld series. You may not see the header when you browse trivia, but it is there. Users of linux based systems can easily inspect the headers using curl (“curl -I https://baldric.net” will list them for you).

The header in question is a reference to the “Clacks” which is a technology in the Discworld much like the telegraph (or internet) of our world. The name comes from the noise that the technology made in use (it “clacked”). The rather lovely xclacksoverhead website gives a nice explanation of the origins of the header.

It was whilst visiting that site today that I discovered that there appear to be over 1300 websites out there which similarly include the X-Clacks-Overhead header, including Debian, Mozilla and, strikingly, the UK Passport Office. It is good to see that even officialdom can show support, albeit in a non-obvious way. I salute the unknown sysadmin for the passport office site.

The header can be added to many services other than just webservers. Adrian Kennard even managed to include it in his company’s Firebrick series of network appliances as padding in the code to handle small Ethernet packets (under 64 bytes). A nice listing of ways to include the header in many other services (from CMSs like wordpress to email servers like postfix or sendmail) can be found at gnuterrypratchett.com. Indeed, following the advice on that page for postfix, I have today added the header to my postfix configuration. I cannot understand why I missed that at the time I changed my lighty config.

A more visible tribute to Sir Terry has long been included in the footer to all pages on trivia where I give the following quote from “Snuff”:

“Cheery was aware that Commander Vimes didn’t like the phrase ‘The innocent have nothing to fear’, believing the innocent had everything to fear, mostly from the guilty but in the longer term even more from those who say things like ‘The innocent have nothing to fear’.”

The world lost a monumental talent when Sir Terry died in 2015. I like to think that he would have loved the way his memory is kept alive in a way which references one of his own works.

Permanent link to this article: https://baldric.net/2023/03/09/x-clacks-overhead/