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MSYNC(2)                   Linux Programmer's Manual                  MSYNC(2)

       msync - synchronize a file with a memory map

       #include <sys/mman.h>

       int msync(void *addr, size_t length, int flags);

       msync()  flushes  changes  made to the in-core copy of a file that was mapped into memory using mmap(2) back to
       disk.  Without use of this call there is no guarantee that changes are written back before munmap(2) is called.
       To be more precise, the part of the file that corresponds to the memory area starting at addr and having length
       length is updated.

       The flags argument may have the bits MS_ASYNC, MS_SYNC, and  MS_INVALIDATE  set,  but  not  both  MS_ASYNC  and
       MS_SYNC.   MS_ASYNC  specifies that an update be scheduled, but the call returns immediately.  MS_SYNC asks for
       an update and waits for it to complete.  MS_INVALIDATE asks to invalidate other mappings of the same  file  (so
       that they can be updated with the fresh values just written).

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

       EBUSY  MS_INVALIDATE was specified in flags, and a memory lock exists for the specified address range.

       EINVAL addr  is  not a multiple of PAGESIZE; or any bit other than MS_ASYNC | MS_INVALIDATE | MS_SYNC is set in
              flags; or both MS_SYNC and MS_ASYNC are set in flags.

       ENOMEM The indicated memory (or part of it) was not mapped.


       This call was introduced in Linux 1.3.21, and then used EFAULT instead of ENOMEM.  In  Linux  2.4.19  this  was
       changed to the POSIX value ENOMEM.

       On POSIX systems on which msync() is available, both _POSIX_MAPPED_FILES and _POSIX_SYNCHRONIZED_IO are defined
       in <unistd.h> to a value greater than 0.  (See also sysconf(3).)

       B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.

       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

Linux                             2008-04-22                          MSYNC(2)