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+.\" Copyright (c) 2000 Sheldon Hearn <sheldonh@FreeBSD.org>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 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
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd July 14, 2000
+.Dt SYNCER 4
+.Os
+.Sh NAME
+.Nm syncer
+.Nd file system synchronizer kernel process
+.Sh SYNOPSIS
+.Nm
+.Sh DESCRIPTION
+The
+.Nm
+kernel process helps protect the integrity of disk volumes
+by flushing volatile cached file system data to disk.
+.Pp
+The kernel places all
+.Xr vnode 9 Ns 's
+in a number of queues.
+The
+.Nm
+process works through the queues
+in a round-robin fashion,
+usually processing one queue per second.
+For each
+.Xr vnode 9
+on that queue,
+the
+.Nm
+process forces a write out to disk of its dirty buffers.
+.Pp
+The usual delay between the time buffers are dirtied
+and the time they are synced
+is controlled by the following
+.Xr sysctl 8
+tunable variables:
+.Bl -column "filedelayXXXX" "DefaultXX" "DescriptionXX"
+.It Em Variable Ta Em Default Ta Em Description
+.It Va kern.filedelay Ta 30 Ta "time to delay syncing files"
+.It Va kern.dirdelay Ta 29 Ta "time to delay syncing directories"
+.It Va kern.metadelay Ta 28 Ta "time to delay syncing metadata"
+.El
+.Sh SEE ALSO
+.Xr sync 2 ,
+.Xr fsck 8 ,
+.Xr sync 8 ,
+.Xr sysctl 8
+.Sh HISTORY
+The
+.Nm
+process is a descendant of the
+.Sq update
+command, which appeared in
+.At v6 ,
+and was usually started by
+.Pa /etc/rc
+when the system went multi-user.
+A kernel initiated
+.Sq update
+process first appeared in
+.Fx 2.0 .
+.Sh BUGS
+It is possible on some systems that a
+.Xr sync 2
+occurring simultaneously with a crash may cause
+file system damage.
+See
+.Xr fsck 8 .