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.
The mlockall() function shall cause all of the pages mapped by the
address space of a process to be memory-resident until unlocked or
until the process exits or execs another process image. The flags
argument determines whether the pages to be locked are those
currently mapped by the address space of the process, those that are
mapped in the future, or both. The flags argument is constructed from
the bitwise-inclusive OR of one or more of the following symbolic
constants, defined in <sys/mman.h>:
MCL_CURRENT Lock all of the pages currently mapped into the address
space of the process.
MCL_FUTURE Lock all of the pages that become mapped into the address
space of the process in the future, when those mappings
If MCL_FUTURE is specified, and the automatic locking of future
mappings eventually causes the amount of locked memory to exceed the
amount of available physical memory or any other implementation-
defined limit, the behavior is implementation-defined. The manner in
which the implementation informs the application of these situations
is also implementation-defined.
The munlockall() function shall unlock all currently mapped pages of
the address space of the process. Any pages that become mapped into
the address space of the process after a call to munlockall() shall
not be locked, unless there is an intervening call to mlockall()
specifying MCL_FUTURE or a subsequent call to mlockall() specifying
MCL_CURRENT. If pages mapped into the address space of the process
are also mapped into the address spaces of other processes and are
locked by those processes, the locks established by the other
processes shall be unaffected by a call by this process to
Upon successful return from the mlockall() function that specifies
MCL_CURRENT, all currently mapped pages of the address space of the
process shall be memory-resident and locked. Upon return from the
munlockall() function, all currently mapped pages of the address
space of the process shall be unlocked with respect to the address
space of the process. The memory residency of unlocked pages is
Appropriate privileges are required to lock process memory with
Upon successful completion, the mlockall() function shall return a
value of zero. Otherwise, no additional memory shall be locked, and
the function shall return a value of −1 and set errno to indicate the
error. The effect of failure of mlockall() on previously existing
locks in the address space is unspecified.
If it is supported by the implementation, the munlockall() function
shall always return a value of zero. Otherwise, the function shall
return a value of −1 and set errno to indicate the error.
The mlockall() function shall fail if:
EAGAIN Some or all of the memory identified by the operation could
not be locked when the call was made.
EINVAL The flags argument is zero, or includes unimplemented flags.
The mlockall() function may fail if:
ENOMEM Locking all of the pages currently mapped into the address
space of the process 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.
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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
IEEE/The Open Group 2013 MLOCKALL(3P)