MLOCKALL(P) POSIX Programmer's Manual MLOCKALL(P)
mlockall, munlockall - lock/unlock the address space of a process (REALTIME)
int mlockall(int flags);
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 cur-
rently 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>:
Lock all of the pages currently mapped into the address space of the process.
Lock all of the pages that become mapped into the address space of the process in
the future, when those mappings are established.
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-
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 mlock-
all() 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 munlockall().
Upon successful return from the mlockall() function that specifies MCL_CURRENT, all cur-
rently mapped pages of the process' address space shall be memory-resident and locked.
Upon return from the munlockall() function, all currently mapped pages of the process'
address space shall be unlocked with respect to the process' address space. The memory
residency of unlocked pages is unspecified.
The appropriate privilege is required to lock process memory with mlockall().
Upon successful completion, the mlockall() function shall return a value of zero. Other-
wise, 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 indi-
cate 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 the appropriate privilege to perform the
The following sections are informative.
exec() , exit() , fork() , mlock() , munmap() , the Base Definitions volume of
IEEE Std 1003.1-2001, <sys/mman.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 MLOCKALL(P)