This hasn't been a thing since the late 90s. Linux used to use a fork of an earlier, pre-linux gnu libc. Glibc2 was a big release where upstream gnu libc was wh

This hasn't been a thing since the late 90s. Linux used to use a fork of an earlier, pre-linux gnu libc. Glibc2 was a big release where upstream gnu libc was what Linux distros used for the first time. Despite being version 2.0, they set the so version to 6 because the Linux specific fork had reached version 5. That is why libc6 is synonymous with glibc2. Here is what I found on Google trying to confirm these memories: https://lwn.net/Articles/417848/ https://lwn.net/Articles/417848/ There were other examples from the gnu world where an experimental fork ends up with rapid development and then gets superseded by an upstream release. Egcs vs gcc is another I remember from that time period.