msync(2) [linux man page]

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.  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  corre-
       sponds 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 3.27 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)

Check Out this Related Man Page

MSYNC(2)						      BSD System Calls Manual							  MSYNC(2)

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.

BSD
								  March 18, 2012							       BSD

Linux and UNIX Man Pages

msync(2) [linux man page]

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