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RedHat 9 (Linux i386) - man page for getpagesize (redhat section 2)

GETPAGESIZE(2)						     Linux Programmer's Manual						    GETPAGESIZE(2)

getpagesize - get memory page size
#include <unistd.h> int getpagesize(void);
The function getpagesize() returns the number of bytes in a page, where a "page" is the thing used where it says in the description of mmap(2) that files are mapped in page-sized units. The size of the kind of pages that mmap uses, is found using #include <unistd.h> long sz = sysconf(_SC_PAGESIZE); (where some systems also allow the synonym _SC_PAGE_SIZE for _SC_PAGESIZE), or #include <unistd.h> int sz = getpagesize();
This call first appeared in 4.2BSD.
SVr4, 4.4BSD, SUSv2. In SUSv2 the getpagesize() call is labeled "legacy", and in POSIX 1003.1-2001 it has been dropped. HPUX does not have this call.
Whether getpagesize() is present as a Linux system call depends on the architecture. If it is, it returns the kernel symbol PAGE_SIZE, which is architecture and machine model dependent. Generally, one uses binaries that are architecture but not machine model dependent, in order to have a single binary distribution per architecture. This means that a user program should not find PAGE_SIZE at compile time from a header file, but use an actual system call, at least for those architectures (like sun4) where this dependency exists. Here libc4, libc5, glibc 2.0 fail because their getpagesize() returns a statically derived value, and does not use a system call. Things are OK in glibc 2.1.
mmap(2), sysconf(3) Linux 2.5.0 2001-12-21 GETPAGESIZE(2)