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@(#)msync.2 8.2 (Berkeley) 6/21/94
.Dd May 9, 2014 .Dt MSYNC 2 .Os .Sh NAME .Nm msync .Nd synchronize a mapped region .Sh LIBRARY .Lb libc .Sh SYNOPSIS n sys/mman.h .Ft int .Fn msync "void *addr" "size_t len" "int flags" .Sh DESCRIPTION The .Fn msync system call writes all pages with shared modifications in the specified region of the process's address space back to permanent storage, and, if requested, invalidates cached data mapped in the region. If .Fa len is 0, all modified pages within the region containing .Fa addr will be flushed; if .Fa len is non-zero, only modified pages containing .Fa addr and .Fa len succeeding locations will be flushed. Any required synchronization of memory caches will also take place at this time. Filesystem operations on a file that is mapped for shared modifications are unpredictable except after an .Fn msync .
p The .Fa flags argument is formed by .Em or Ns 'ing the following values
p l -column -offset indent -compact MS_INVALIDATE t Dv MS_ASYNC Ta Perform asynchronous writes. t Dv MS_SYNC Ta Perform synchronous writes. t Dv MS_INVALIDATE Ta Invalidate cached data after writing. .El .Sh RETURN VALUES Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and .Va errno is set to indicate the error. .Sh ERRORS The following errors may be reported: l -tag -width Er t Bq Er EBUSY The .Dv MS_INVALIDATE flag was specified and a portion of the specified region was locked with .Xr mlock 2 . t Bq Er EINVAL The specified .Fa flags argument was invalid. t Bq Er EINVAL The .Fa addr parameter was not page aligned. t Bq Er EINVAL The .Fa addr parameter did not specify an address part of a mapped region. t Bq Er EIO An I/O error occurred while writing to the file system. t Bq Er ENOMEM Addresses in the specified region are outside the range allowed for the address space of the process, or specify one or more pages which are unmapped. .El .Sh SEE ALSO .Xr mlock 2 , .Xr mmap 2 , .Xr munlock 2 .Sh STANDARDS The .Fn msync function conforms to .St -p1003.1b-93 .Sh HISTORY The .Fn msync function first appeared in x 4.4 . It was modified to conform to .St -p1003.1b-93 in .Nx 1.3 .
Indexes created Sat Sep 20 22:09:52 GMT 2025