Provided by: manpages-posix-dev_2.16-1_all 
NAME
mlock, munlock - lock or unlock a range of process address space (REALTIME)
SYNOPSIS
#include <sys/mman.h>
int mlock(const void *addr, size_t len);
int munlock(const void *addr, size_t len);
DESCRIPTION
The mlock() function shall cause those whole pages containing any part of the address space of the
process starting at address addr and continuing for len bytes to be memory-resident until unlocked or
until the process exits or execs another process image. The implementation may require that addr be a
multiple of {PAGESIZE}.
The munlock() function shall unlock those whole pages containing any part of the address space of the
process starting at address addr and continuing for len bytes, regardless of how many times mlock() has
been called by the process for any of the pages in the specified range. The implementation may require
that addr be a multiple of {PAGESIZE}.
If any of the pages in the range specified to a call to munlock() are also mapped into the address spaces
of other processes, any locks established on those pages by another process are unaffected by the call of
this process to munlock(). If any of the pages in the range specified by a call to munlock() are also
mapped into other portions of the address space of the calling process outside the range specified, any
locks established on those pages via the other mappings are also unaffected by this call.
Upon successful return from mlock(), pages in the specified range shall be locked and memory-resident.
Upon successful return from munlock(), pages in the specified range shall be unlocked with respect to the
address space of the process. Memory residency of unlocked pages is unspecified.
The appropriate privilege is required to lock process memory with mlock().
RETURN VALUE
Upon successful completion, the mlock() and munlock() functions shall return a value of zero. Otherwise,
no change is made to any locks in the address space of the process, and the function shall return a value
of -1 and set errno to indicate the error.
ERRORS
The mlock() and munlock() functions shall fail if:
ENOMEM Some or all of the address range specified by the addr and len arguments does not correspond to
valid mapped pages in the address space of the process.
The mlock() function shall fail if:
EAGAIN Some or all of the memory identified by the operation could not be locked when the call was made.
The mlock() and munlock() functions may fail if:
EINVAL The addr argument is not a multiple of {PAGESIZE}.
The mlock() function may fail if:
ENOMEM Locking the pages mapped by the specified range would exceed an implementation-defined limit on
the amount of memory that the process may lock.
EPERM The calling process does not have the appropriate privilege to perform the requested operation.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
exec() , exit() , fork() , mlockall() , munmap() , the Base Definitions volume of IEEE Std 1003.1-2001,
<sys/mman.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .