186d7f5d3SJohn Marino.\" Copyright (c) 2000 Sheldon Hearn <sheldonh@FreeBSD.org> 286d7f5d3SJohn Marino.\" All rights reserved. 386d7f5d3SJohn Marino.\" 486d7f5d3SJohn Marino.\" Redistribution and use in source and binary forms, with or without 586d7f5d3SJohn Marino.\" modification, are permitted provided that the following conditions 686d7f5d3SJohn Marino.\" are met: 786d7f5d3SJohn Marino.\" 1. Redistributions of source code must retain the above copyright 886d7f5d3SJohn Marino.\" notice, this list of conditions and the following disclaimer. 986d7f5d3SJohn Marino.\" 2. Redistributions in binary form must reproduce the above copyright 1086d7f5d3SJohn Marino.\" notice, this list of conditions and the following disclaimer in the 1186d7f5d3SJohn Marino.\" documentation and/or other materials provided with the distribution. 1286d7f5d3SJohn Marino.\" 1386d7f5d3SJohn Marino.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 1486d7f5d3SJohn Marino.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 1586d7f5d3SJohn Marino.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 1686d7f5d3SJohn Marino.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 1786d7f5d3SJohn Marino.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 1886d7f5d3SJohn Marino.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 1986d7f5d3SJohn Marino.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 2086d7f5d3SJohn Marino.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 2186d7f5d3SJohn Marino.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 2286d7f5d3SJohn Marino.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 2386d7f5d3SJohn Marino.\" SUCH DAMAGE. 2486d7f5d3SJohn Marino.\" 2586d7f5d3SJohn Marino.\" $FreeBSD: src/share/man/man4/syncer.4,v 1.3.2.5 2001/07/21 09:16:47 schweikh Exp $ 2686d7f5d3SJohn Marino.\" $DragonFly: src/share/man/man4/syncer.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ 2786d7f5d3SJohn Marino.\" 2886d7f5d3SJohn Marino.Dd July 14, 2000 2986d7f5d3SJohn Marino.Dt SYNCER 4 3086d7f5d3SJohn Marino.Os 3186d7f5d3SJohn Marino.Sh NAME 3286d7f5d3SJohn Marino.Nm syncer 3386d7f5d3SJohn Marino.Nd filesystem synchronizer kernel process 3486d7f5d3SJohn Marino.Sh SYNOPSIS 3586d7f5d3SJohn Marino.Nm 3686d7f5d3SJohn Marino.Sh DESCRIPTION 3786d7f5d3SJohn MarinoThe 3886d7f5d3SJohn Marino.Nm 3986d7f5d3SJohn Marinokernel process helps protect the integrity of disk volumes 4086d7f5d3SJohn Marinoby flushing volatile cached filesystem data to disk. 4186d7f5d3SJohn Marino.Pp 4286d7f5d3SJohn MarinoThe kernel places all 4386d7f5d3SJohn Marino.Xr vnode 9 Ns 's 4486d7f5d3SJohn Marinoin a number of queues. 4586d7f5d3SJohn MarinoThe 4686d7f5d3SJohn Marino.Nm 4786d7f5d3SJohn Marinoprocess works through the queues 4886d7f5d3SJohn Marinoin a round-robin fashion, 4986d7f5d3SJohn Marinousually processing one queue per second. 5086d7f5d3SJohn MarinoFor each 5186d7f5d3SJohn Marino.Xr vnode 9 5286d7f5d3SJohn Marinoon that queue, 5386d7f5d3SJohn Marinothe 5486d7f5d3SJohn Marino.Nm 5586d7f5d3SJohn Marinoprocess forces a write out to disk of its dirty buffers. 5686d7f5d3SJohn Marino.Pp 5786d7f5d3SJohn MarinoThe usual delay between the time buffers are dirtied 5886d7f5d3SJohn Marinoand the time they are synced 5986d7f5d3SJohn Marinois controlled by the following 6086d7f5d3SJohn Marino.Xr sysctl 8 6186d7f5d3SJohn Marinotunable variables: 6286d7f5d3SJohn Marino.Bl -column "filedelayXXXX" "DefaultXX" "DescriptionXX" 6386d7f5d3SJohn Marino.It Em Variable Ta Em Default Ta Em Description 6486d7f5d3SJohn Marino.It Va kern.filedelay Ta 30 Ta "time to delay syncing files" 6586d7f5d3SJohn Marino.It Va kern.dirdelay Ta 29 Ta "time to delay syncing directories" 6686d7f5d3SJohn Marino.It Va kern.metadelay Ta 28 Ta "time to delay syncing metadata" 6786d7f5d3SJohn Marino.El 6886d7f5d3SJohn Marino.Sh SEE ALSO 6986d7f5d3SJohn Marino.Xr sync 2 , 7086d7f5d3SJohn Marino.Xr fsck 8 , 7186d7f5d3SJohn Marino.Xr sync 8 , 7286d7f5d3SJohn Marino.Xr sysctl 8 7386d7f5d3SJohn Marino.Sh HISTORY 7486d7f5d3SJohn MarinoThe 7586d7f5d3SJohn Marino.Nm 7686d7f5d3SJohn Marinoprocess is a descendant of the 7786d7f5d3SJohn Marino.Sq update 7886d7f5d3SJohn Marinocommand, which appeared in 7986d7f5d3SJohn Marino.At v6 , 8086d7f5d3SJohn Marinoand was usually started by 8186d7f5d3SJohn Marino.Pa /etc/rc 8286d7f5d3SJohn Marinowhen the system went multi-user. 8386d7f5d3SJohn MarinoA kernel initiated 8486d7f5d3SJohn Marino.Sq update 8586d7f5d3SJohn Marinoprocess first appeared in 8686d7f5d3SJohn Marino.Fx 2.0 . 8786d7f5d3SJohn Marino.Sh BUGS 8886d7f5d3SJohn MarinoIt is possible on some systems that a 8986d7f5d3SJohn Marino.Xr sync 2 9086d7f5d3SJohn Marinooccurring simultaneously with a crash may cause 9186d7f5d3SJohn Marinofile system damage. See 9286d7f5d3SJohn Marino.Xr fsck 8 . 93