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NAME

       msync - synchronize a file with a memory map

SYNOPSIS

       #include <sys/mman.h>

       int msync(void *start, 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.   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 start 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

       EINVAL start is not a multiple of  PAGESIZE,  or  any  bit  other  than
              MS_ASYNC | MS_INVALIDATE | MS_SYNC is set in flags.

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

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).)

CONFORMING TO

       POSIX.1b (formerly POSIX.4)

       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.

SEE ALSO

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