getpagesize(2)

NAME
getpagesize - get memory page size

LIBRARY
Standard C library (libc, -lc)

SYNOPSIS
#include <unistd.h>

int getpagesize(void);

    Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

getpagesize():
    Since glibc 2.20:
        _DEFAULT_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
    glibc 2.12 to glibc 2.19:
        _BSD_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
    Before glibc 2.12:
        _BSD_SOURCE || _XOPEN_SOURCE >= 500

DESCRIPTION
The function getpagesize() returns the number of bytes in a memory page, where "page" is a fixed-length block, the unit for memory allocation and file mapping performed by mmap(2).

STANDARDS
None.

HISTORY
This call first appeared in 4.2BSD. SVr4, 4.4BSD, SUSv2. In SUSv2 the getpagesize() call is labeled LEGACY, and in POSIX.1-2001 it has been dropped; HP-UX does not have this call.

NOTES
Portable applications should employ sysconf(_SC_PAGESIZE) instead of getpagesize():

    #include <unistd.h>
    long sz = sysconf(_SC_PAGESIZE);

(Most systems allow the synonym _SC_PAGE_SIZE for _SC_PAGESIZE.)

Whether getpagesize() is present as a Linux system call depends on the architecture. If it is, it returns the kernel symbol PAGE_SIZE, whose value depends on the architecture and machine model. Generally, one uses binaries that are dependent on the architecture but not on the machine model, 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 glibc 2.0 fails because its getpagesize() returns a statically derived value, and does not use a system call. Things are OK in glibc 2.1.

SEE ALSO
mmap(2), sysconf(3)