getpagesize(2) System Calls Manual 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 alloca- tion and file mapping performed by mmap(2). STANDARDS 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 ma- chine model, in order to have a single binary distribution per archi- tecture. 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 de- rived value, and does not use a system call. Things are OK in glibc 2.1. SEE ALSO mmap(2), sysconf(3) Linux man-pages 6.03 2023-02-05 getpagesize(2)
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