Linus Torvalds, the creator of the Linux kernel, has finally discovered the date of its first release: September 17, 1991. Twenty-five years later, to the day, Torvalds posted this message on his Google+ page:

Today is the 25th anniversary of the Linux-0.01 release, I do believe.

Normally the Linux anniversary is counted from the announcement email, which was August 25, because that was the actual public statement of intent. The 0.01 code drop happened a couple of weeks later and wasn't publicly announced.

Earlier during an interview with Linux Pro Magazine, Torvalds said he was not sure about the actual Linux anniversary day, because there was possibly more than one date. Although August 25 is the date he announced the project he was working on, Torvalds said he never announced the first release publicly and simply uploaded it to an FTP server and emailed those who were interested in it.

Since then, he said, he lost all those email communications, so he didn’t remember exactly when the first version of Linux was released. The only way to find out, he said, was to look at the timestamp on the first release. That’s exactly what he seems to have done: The makefile of the first release is stamped September 17, 1991.

However, that doesn’t change the official birthday of Linux. Torvalds settled that matter during a keynote discussion at LinuxCon North America (Toronto) when he said August 25 is the official date to use as a birthday.