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mlock(3)
NAME
  mlock, munlock - Lock or unlock a specified region in memory (P1003.1b)

SYNOPSIS
  #include <sys/mman.h>

  int mlock (
  const void *addr,
  size_t len);

  int munlock (
  const void *addr,
  size_t len);

PARAMETERS
  *addr	  A pointer to the starting address of the region to lock or unlock.
	  The addr argument must be a multiple of the page size returned by
	  the sysconf system call.

  len	  The size of the memory region to lock or unlock.  The value of len
	  is rounded up to a multiple of the page size before decrementing by
	  1.

DESCRIPTION
  The mlock and munlock functions lock and unlock whole pages containing any
  part of the process address space starting at addr and continuing for len
  bytes.

  The mlock function guarantees all whole pages mapped by the range addr to
  addr+len-1 (inclusive) to be memory resident.	 (The area locked is the same
  as if the len argument were rounded up to a multiple of the page size
  before decrementing by 1.)

  The locked area remains locked until unlocked with a call to the munlock
  function, the process calls the exec function, an address space associated
  with the lock is unmapped, or the process terminates.	 A lock is not
  inherited across a fork or an exec.

  The munlock function unlocks whole pages previously mapped by the range
  addr to addr+len-1 (inclusive), regardless of how many times the mlock
  function was called by the process for any pages within the specified
  range.

  A call to the munlock function does not affect pages that may be mapped
  into another process's address space or locked by another process.

  You must have superuser privileges to call the mlock or munlock functions.



RETURN VALUES
  On a successful call to the mlock function, a value of 0 is returned and
  the region becomes locked and memory resident.  On an unsuccessful call, a
  value of -1 is returned, no changes are made to any locks in the process
  address space, and errno is set to indicate that an error occurred.

  On a successful call to the munlock function, a value of 0 is returned and
  the memory is unlocked with respect to the process's address space. On an
  unsuccessful call, a value of -1 is returned, none of the memory is
  unlocked, and errno is set to indicate that an error occurred.

ERRORS
  The mlock and munlock functions fail under the following conditions:

  [EINVAL]	 The addr argument is not a multiple of the page size
		 returned by sysconf.

  [ENOMEM]	 Some or all of the address range specified by the addr and
		 len arguments does not correspond to valid mapped pages in
		 the process's address space.  For the mlock function,
		 locking the pages mapped by the specified range would exceed
		 an implementation-defined limit on the amount of memory that
		 the process may lock.

  If any of the following conditions occur, the mlock function shall fail:

  [EAGAIN]	 Some or all of the memory identified by the operation could
		 not be locked when the call was made.

  [EPERM]	 The calling process does not have the appropriate privileges
		 to perform the requested operation.

RELATED INFORMATION
  Functions: exec(2), _exit(2), fork(2), munmap(2), sysconf(3)

Index for Section 3

Alphabetical listing for M

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