mincore — determine whether pages are resident in memory


#include <sys/mman.h>
int mincore( void *addr,
  size_t length,
  unsigned char *vec);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Since glibc 2.19:
_DEFAULT_SOURCE Glibc 2.19 and earlier:


mincore() returns a vector that indicates whether pages of the calling process's virtual memory are resident in core (RAM), and so will not cause a disk access (page fault) if referenced. The kernel returns residency information about the pages starting at the address addr, and continuing for length bytes.

The addr argument must be a multiple of the system page size. The length argument need not be a multiple of the page size, but since residency information is returned for whole pages, length is effectively rounded up to the next multiple of the page size. One may obtain the page size (PAGE_SIZE) using sysconf(_SC_PAGESIZE).

The vec argument must point to an array containing at least (length+PAGE_SIZE−1) / PAGE_SIZE bytes. On return, the least significant bit of each byte will be set if the corresponding page is currently resident in memory, and be clear otherwise. (The settings of the other bits in each byte are undefined; these bits are reserved for possible later use.) Of course the information returned in vec is only a snapshot: pages that are not locked in memory can come and go at any moment, and the contents of vec may already be stale by the time this call returns.


On success, mincore() returns zero. On error, −1 is returned, and errno is set to indicate the error.


EAGAIN kernel is temporarily out of resources.


vec points to an invalid address.


addr is not a multiple of the page size.


length is greater than (TASK_SIZEaddr). (This could occur if a negative value is specified for length, since that value will be interpreted as a large unsigned integer.) In Linux 2.6.11 and earlier, the error EINVAL was returned for this condition.


addr to addr + length contained unmapped memory.


Available since Linux 2.3.99pre1 and glibc 2.2.


mincore() is not specified in POSIX.1, and it is not available on all UNIX implementations.


Before kernel 2.6.21, mincore() did not return correct information for MAP_PRIVATE mappings, or for nonlinear mappings (established using remap_file_pages(2)).


fincore(1), madvise(2), mlock(2), mmap(2), posix_fadvise(2), posix_madvise(3)


This page is part of release 5.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at−pages/.

  Copyright (C) 2001 Bert Hubert <>
and Copyright (C) 2007 Michael Kerrisk <>

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.

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Since the Linux kernel and libraries are constantly changing, this
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Formatted or processed versions of this manual, if unaccompanied by
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Created Sun Jun 3 17:23:32 2001 by bert hubert <>
Slightly adapted, following comments by Hugh Dickins, aeb, 2001-06-04.
Modified, 20 May 2003, Michael Kerrisk <>
Modified, 30 Apr 2004, Michael Kerrisk <>
2005-04-05 mtk, Fixed error descriptions
after message from <>
2007-01-08 mtk, rewrote various parts