The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> mlock, munlock - lock or unlock a range of process address space (REALTIME)

#### SYNOPSIS

> ``[MLR] #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

> XBD <sys/mman.h>

#### CHANGE HISTORY

> First released in Issue 5. Included for alignment with the POSIX Realtime Extension.

#### Issue 6

> The mlock() and munlock() functions are marked as part of the Range Memory Locking option.

> The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Range Memory Locking option.

End of informative text.

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