MLOCK(3)                   POSIX Programmer's Manual                  MLOCK(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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.

       Appropriate privileges are 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 appropriate privileges 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 POSIX.1-2017, <sys_mman.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                             MLOCK(3)
