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mlock(3)							      mlock(3)

NAME
       mlock,  munlock	-  Locks  or  unlocks  a  specified  region  in memory
       (P1003.1b)

SYNOPSIS
       #include <sys/mman.h>

       int mlock ( const void *addr, size_t len);

       int munlock ( const void *addr, size_t len);

LIBRARY
       Realtime Library (librt.so, librt.a)

PARAMETERS
       A pointer to the starting address of the region to lock or unlock.  The
       addr  argument  must  be	 a  multiple  of the page size returned by the
       sysconf system call.  The size of the memory region to lock or  unlock.
       The  value  of  len is rounded up to a multiple of the page size before
       decrementing by 1.

DESCRIPTION
       The mlock and munlock functions lock and unlock whole pages  containing
       any  part  of the process address space starting at addr and continuing
       for len bytes.

       The mlock function guarantees all whole pages mapped by the range  addr
       to  addr+len-1  (inclusive)  to be memory resident. (The area locked is
       the same	 as if the len argument were rounded up to a multiple  of  the
       page size before decrementing by 1.)

       The  locked  area  remains  locked  until  unlocked  with a call to the
       munlock function, until the process calls the exec function,  until  an
       address	space  associated  with	 the  lock  is	unmapped, or until the
       process terminates. A lock is not inherited across a fork or an exec.

       The mlock function unlocks whole pages previously mapped by  the	 range
       addr  to addr+len-1 (inclusive), regardless of how many times the mlock
       function was called by the process for any pages within	the  specified
       range.

       A call to the munlock function does not affect pages that may be mapped
       into another process's address space or locked by another process.

       You must have superuser privileges to call the mlock or munlock	 func‐
       tions.

RETURN VALUES
       On  a  successful  call	to  the mlock function, a value of 0 (zero) is
       returned and the region becomes locked  and  memory  resident.	On  an
       unsuccessful  call,  a  value of -1 is returned, no changes are made to
       any locks in the process address space, and errno is  set  to  indicate
       that an error occurred.

       On  a  successful  call to the munlock function, a value of 0 (zero) is
       returned and the memory is  unlocked  with  respect  to	the  process's
       address space. On an unsuccessful call, a value of -1 is returned, none
       of the memory is unlocked, and errno is set to indicate that  an	 error
       occurred.

ERRORS
       The  mlock  and	munlock functions fail under the following conditions:
       The addr argument is not a  multiple  of	 the  page  size  returned  by
       sysconf.	  Some	or  all of the address range specified by the addr and
       len arguments  does  not	 correspond  to	 valid	mapped	pages  in  the
       process's  address  space.  For	the  mlock function, locking the pages
       mapped by the specified range would  exceed  an	implementation-defined
       limit on the amount of memory that the process may lock.

       If  any	of  the	 following conditions occur, the mlock function fails:
       Some or all of the memory identified by	the  operation	could  not  be
       locked  when  the call was made.	 The calling process does not have the
       appropriate privileges to perform the requested operation.

SEE ALSO
       Functions: exec(2), _exit(2), fork(2), munmap(2), sysconf(3)

       Guide to Realtime Programming

								      mlock(3)
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