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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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MLOCK(3P) POSIX Programmer's Manual MLOCK(3P)
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.
mlock, munlock — lock or unlock a range of process address space
(REALTIME)
#include <sys/mman.h>
int mlock(const void *addr, size_t len);
int munlock(const void *addr, size_t len);
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().
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.
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.
None.
None.
None.
None.
exec(1p), exit(3p), fork(3p), mlockall(3p), munmap(3p)
The Base Definitions volume of POSIX.1‐2017, sys_mman.h(0p)
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(3P)
Pages that refer to this page: sys_mman.h(0p), _Exit(3p), mlockall(3p), munlock(3p), munmap(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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