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)