This is the Debian GNU/Linux prepackaged version of the POSIX manual pages. These pages were originally maintained by Rik Faith and then taken over by Andries Brouwer , under permission of IEEE Open Group. POSIX manpages are maintained under separate 0p,1p and 3p sections, but this convention is not conforming with FHS, so they are moved in 7, 1 and 3 respectively, with extensions 7posix, 1posix and 3posix. So you can use man 3 -e 3posix to access POSIX functions description instead of Linux one. Having manpages is very important to every operating system. It is much work to keep those documents up to date and to initially write them. Nevertheless some folks made some of this work. Contributions are welcome.