The GNU C Library
1.2.3 Berkeley Unix
The GNU C library defines facilities from some versions of Unix which
are not formally standardized, specifically from the 4.2 BSD, 4.3 BSD,
and 4.4 BSD Unix systems (also known as Berkeley Unix) and from
SunOS (a popular 4.2 BSD derivative that includes some Unix System
V functionality). These systems support most of the ISO C and POSIX
facilities, and 4.4 BSD and newer releases of SunOS in fact support them all.
The BSD facilities include symbolic links (see section 14.5 Symbolic Links), the
select function (see section 13.8 Waiting for Input or Output), the BSD signal
functions (see section 24.10 BSD Signal Handling), and sockets (see section 16. Sockets).