Provided by: freebsd-manpages_8.2-1_all
msync — synchronize a mapped region
Standard C Library (libc, -lc)
msync(void *addr, size_t len, int flags);
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
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
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
[EINVAL] The len argument is too large or negative.
[EINVAL] The flags argument was both MS_ASYNC and
MS_INVALIDATE. Only one of these flags is allowed.
madvise(2), mincore(2), mlock(2), mprotect(2), munmap(2)
The msync() system call first appeared in 4.4BSD.
The msync() system call is obsolete since BSD implements a coherent file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.