NAME

       msync — synchronize a mapped region

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

       #include <sys/mman.h>

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

DESCRIPTION

       The  msync()  system  call  writes  any  modified  pages  back  to  the  file system and updates the file
       modification time.  If len is 0, all modified pages within the region containing addr will be flushed; if
       len is non-zero, only those pages containing addr and len-1 succeeding locations will be  examined.   The
       flags argument may be specified as follows:

       MS_ASYNC       Return immediately
       MS_SYNC        Perform synchronous writes
       MS_INVALIDATE  Invalidate all cached data

RETURN VALUES

       The msync() function returns the value 0 if successful; otherwise the value -1 is returned and the global
       variable errno is set to indicate the error.

ERRORS

       The msync() system call will fail if:

       [EBUSY]            Some  or  all  of  the  pages  in the specified region are locked and MS_INVALIDATE is
                          specified.

       [EINVAL]           The addr argument is not a multiple of the hardware page size.

       [ENOMEM]           The addresses in the range starting at addr and continuing for len bytes  are  outside
                          the range allowed for the address space of a process or specify one or more pages that
                          are not mapped.

       [EINVAL]           The  flags  argument  was both MS_ASYNC and MS_INVALIDATE.  Only one of these flags is
                          allowed.

       [EIO]              An error occurred while writing at least one of the pages in the specified region.

SEE ALSO

       madvise(2), mincore(2), mlock(2), mprotect(2), munmap(2)

HISTORY

       The msync() system call first appeared in 4.4BSD.

BUGS

       The msync() system call is usually not needed since BSD implements a coherent file system  buffer  cache.
       However,  it  may  be used to associate dirty VM pages with file system buffers and thus cause them to be
       flushed to physical media sooner rather than later.

Debian                                           March 18, 2012                                         MSYNC(2)