I want to write a small libc for my linux micro-distribution according to the POSIX standard, after googling I realized that it is accepted by the IEEE, if not, then correct me, because I did not really understand these standardizations.

The IEEE site is paid.

How to write according to this standard for free, and where can I get the current version of the standard?

Answer 1, authority 100%

some important versions are published for free access on the organization’s website the open group .

for example:

1. The Single UNIX® Specification, Version 2 © 1997 The Open Group
2. The Open Group Base Specifications Issue 6 IEEE Std 1003.1, 2004 Edition © 2001-2004 The IEEE and The Open Group
3. The Open Group Base Specifications Issue 7 IEEE Std 1003.1 ™, 2013 Edition © 2001-2013 The IEEE and The Open Group