freebsd-dev/lib/libc/sys/sync.2

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.\" Copyright (c) 1980, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
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.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
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.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" @(#)sync.2 8.1 (Berkeley) 6/4/93
1999-08-28 00:22:10 +00:00
.\" $FreeBSD$
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.\"
.Dd June 4, 1993
.Dt SYNC 2
.Os
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.Sh NAME
.Nm sync
.Nd "schedule file system updates"
.Sh LIBRARY
.Lb libc
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.Sh SYNOPSIS
.In unistd.h
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.Ft void
.Fn sync void
.Sh DESCRIPTION
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The
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.Fn sync
system call forces a write of dirty (modified) buffers
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in the block buffer cache out
to disk.
The kernel keeps this information in core to reduce
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the number of disk I/O transfers required by the system.
As information in the cache is lost after a system crash, a
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.Fn sync
system call is issued
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frequently
by the user process
.Xr syncer 4
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(about every 30 seconds).
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.Pp
The
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.Xr fsync 2
system call
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may be used to synchronize individual file descriptor
attributes.
.Sh SEE ALSO
.Xr fsync 2 ,
.Xr syncer 4 ,
.Xr sync 8
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.Sh HISTORY
The
.Fn sync
function appeared in
.At v6 .
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.Sh BUGS
The
.Fn sync
system call
may return before the buffers are completely flushed.