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 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 3.54 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/.