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.\"     @(#)sync.2	8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: January 9 2016 $
.Dt SYNC 2
.Os
.Sh NAME
.Nm sync
.Nd synchronize disk block in-core status with that on disk
.Sh SYNOPSIS
.In unistd.h
.Ft void
.Fn sync void
.Sh DESCRIPTION
The
.Fn sync
function forces a write of dirty (modified) buffers
in the block buffer cache out to disk.
The kernel keeps this information in core to reduce
the number of disk I/O transfers required by the system.
As information in the cache is lost after a system crash a
.Fn sync
call is issued frequently by the in-kernel process update
(about every 30 seconds).
.Pp
The function
.Xr fsync 2
may be used to synchronize individual file descriptor attributes.
.Sh SEE ALSO
.Xr fsync 2 ,
.Xr sync 8
.Sh STANDARDS
The
.Fn sync
function conforms to
.St -p1003.1-2008 .
.Sh HISTORY
A
.Fn sync
function appeared in
.At v2 .
.Sh BUGS
.Fn sync
may return before the buffers are completely flushed.