Return the number of bytes in a page. This is the system's page size, which is not necessarily the same as the hardware page size.
getpagesize(2) is implemented as a library function in DLL 4.4.1. Depending on what is defined when the library is compiled, this function returns EXEC_PAGESIZE (set to 4096 in Linux 0.99.11), NBPG (set to 4096 in Linux 0.99.11), or NBPC (not defined in Linux 0.99.11 or DLL 4.4.1 libraries).
Depending on architecture and library version, this library call may do a system call or not. It may return a value different from that of the system call. For example, on a sun4 with libc5 this routine returns EXEC_PAGESIZE, which is 8192, and not PAGE_SIZE, which is 4096, or the result of the system call, which also is 4096.
SVr4, 4.4BSD (this call first appeared in 4.2BSD).