PROLOG

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

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 .