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# getpagesize() - Unix, Linux System Call

# NAME

getpagesize - get memory page size

# SYNOPSIS

#include <unistd.h>

int getpagesize(void);

# DESCRIPTION

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();

# HISTORY

This call first appeared in 4.2BSD.

# CONFORMING TO

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

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.

# SEE ALSO

- mmap (2)

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