1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.Dd December 1, 2017 29.Dt SYNC 2 30.Os 31.Sh NAME 32.Nm sync 33.Nd "schedule file system updates" 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In unistd.h 38.Ft void 39.Fn sync void 40.Sh DESCRIPTION 41The 42.Fn sync 43system call forces a write of dirty (modified) buffers 44in the block buffer cache out 45to disk. 46The kernel keeps this information in core to reduce 47the number of disk I/O transfers required by the system. 48As information in the cache is lost after a system crash, a 49.Fn sync 50system call is issued 51frequently 52by the kernel process 53.Xr syncer 4 54(about every 30 seconds). 55.Pp 56The 57.Xr fsync 2 58system call 59may be used to synchronize individual file descriptor 60attributes. 61.Sh SEE ALSO 62.Xr fsync 2 , 63.Xr syncer 4 , 64.Xr sync 8 65.Sh HISTORY 66The 67.Fn sync 68function appeared in 69.At v3 . 70.Sh BUGS 71The 72.Fn sync 73system call 74may return before the buffers are completely flushed. 75