| .\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl> |
| .\" |
| .\" %%%LICENSE_START(VERBATIM) |
| .\" Permission is granted to make and distribute verbatim copies of this |
| .\" manual provided the copyright notice and this permission notice are |
| .\" preserved on all copies. |
| .\" |
| .\" Permission is granted to copy and distribute modified versions of this |
| .\" manual under the conditions for verbatim copying, provided that the |
| .\" entire resulting derived work is distributed under the terms of a |
| .\" permission notice identical to this one. |
| .\" |
| .\" Since the Linux kernel and libraries are constantly changing, this |
| .\" manual page may be incorrect or out-of-date. The author(s) assume no |
| .\" responsibility for errors or omissions, or for damages resulting from |
| .\" the use of the information contained herein. The author(s) may not |
| .\" have taken the same level of care in the production of this manual, |
| .\" which is licensed free of charge, as they might when working |
| .\" professionally. |
| .\" |
| .\" Formatted or processed versions of this manual, if unaccompanied by |
| .\" the source, must acknowledge the copyright and authors of this work. |
| .\" %%%LICENSE_END |
| .\" |
| .TH GETPAGESIZE 2 2017-09-15 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| getpagesize \- get memory page size |
| .SH SYNOPSIS |
| .B #include <unistd.h> |
| .PP |
| .B int getpagesize(void); |
| .PP |
| .in -4n |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .in |
| .PP |
| .BR getpagesize (): |
| .ad l |
| .RS 4 |
| .PD 0 |
| .TP 4 |
| Since glibc 2.19: |
| .nf |
| _DEFAULT_SOURCE || ! (_POSIX_C_SOURCE\ >=\ 200112L) |
| .TP 4 |
| .fi |
| From glibc 2.12 to 2.19: |
| .nf |
| _BSD_SOURCE || ! (_POSIX_C_SOURCE\ >=\ 200112L) |
| .TP 4 |
| .fi |
| Before glibc 2.12: |
| _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 |
| .\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED |
| .PD |
| .RE |
| .ad b |
| .SH DESCRIPTION |
| The function |
| .BR 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 |
| .BR mmap (2). |
| .\" .SH HISTORY |
| .\" This call first appeared in 4.2BSD. |
| .SH CONFORMING TO |
| SVr4, 4.4BSD, SUSv2. |
| In SUSv2 the |
| .BR getpagesize () |
| call is labeled LEGACY, and in POSIX.1-2001 |
| it has been dropped; |
| HP-UX does not have this call. |
| .SH NOTES |
| Portable applications should employ |
| .I sysconf(_SC_PAGESIZE) |
| instead of |
| .BR getpagesize (): |
| .PP |
| .in +4n |
| .EX |
| #include <unistd.h> |
| long sz = sysconf(_SC_PAGESIZE); |
| .EE |
| .in |
| .PP |
| (Most systems allow the synonym |
| .B _SC_PAGE_SIZE |
| for |
| .BR _SC_PAGESIZE .) |
| .PP |
| Whether |
| .BR getpagesize () |
| is present as a Linux system call depends on the architecture. |
| If it is, it returns the kernel symbol |
| .BR 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 |
| .B 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 |
| .BR getpagesize () |
| returns a statically derived value, and does not use a system call. |
| Things are OK in glibc 2.1. |
| .SH SEE ALSO |
| .BR mmap (2), |
| .BR sysconf (3) |