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



NAME
       msync - synchronize a file with a memory map

SYNOPSIS
       #include <sys/mman.h>

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

DESCRIPTION
       msync() flushes changes made to the in-core copy of a file that was mapped into memory using mmap(2) back to disk.  With-
       out 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).

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

ERRORS
       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.

CONFORMING TO
       POSIX.1-2001.

       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.

AVAILABILITY
       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).)

SEE ALSO
       mmap(2)
       B.O. Gallmeister, POSIX.4, O'Reilly, pp. 128-129 and 389-391.

COLOPHON
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-04-22                                                   MSYNC(2)