freebsd-skq/share/man/man4/syncer.4

.\" 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 filesystem synchronizer kernel process
.Sh SYNOPSIS
.Nm syncer
.Sh DESCRIPTION
The
.Nm
kernel process helps protect the integrity of disk volumes
by flushing volatile cached filesystem 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
Usually,
buffers will be written out no more than
about 30 seconds
after they are dirtied.
.Sh SEE ALSO
.Xr sync 2 ,
.Xr fsck 8 ,
.Xr sync 8
.Sh HISTORY
The
.Nm
process is a descendant of the
.Sq update
command, which apeared in
.At v6 ,
and was usually started by
.Pa /etc/rc
when the system went multi-user.
A kernel initiated
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 .
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`.\" Copyright (c) 2000 Sheldon Hearn <sheldonh@FreeBSD.org>`
			`.\" All rights reserved.`
Added a update(4) man page to describe the kernel initiated update process and changed all of the old references to update(8) to update(4). 1996-02-12 00:45:47 +00:00			`.\"`
			`.\" 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.`
			`.\"`
$Id$ -> $FreeBSD$ 1999-08-28 00:22:10 +00:00			`.\" $FreeBSD$`
add missing cvs Id lines. 1997-03-07 02:50:01 +00:00			`.\"`
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`.Dd July 14, 2000`
			`.Dt SYNCER 4`
			`.Os`
Added a update(4) man page to describe the kernel initiated update process and changed all of the old references to update(8) to update(4). 1996-02-12 00:45:47 +00:00			`.Sh NAME`
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`.Nm syncer`
			`.Nd filesystem synchronizer kernel process`
Added a update(4) man page to describe the kernel initiated update process and changed all of the old references to update(8) to update(4). 1996-02-12 00:45:47 +00:00			`.Sh SYNOPSIS`
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`.Nm syncer`
Added a update(4) man page to describe the kernel initiated update process and changed all of the old references to update(8) to update(4). 1996-02-12 00:45:47 +00:00			`.Sh DESCRIPTION`
			`The`
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`.Nm`
Added a update(4) man page to describe the kernel initiated update process and changed all of the old references to update(8) to update(4). 1996-02-12 00:45:47 +00:00			`kernel process helps protect the integrity of disk volumes`
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`by flushing volatile cached filesystem data to disk.`
			`.Pp`
			`The kernel places all`
			`.Xr vnode 9 Ns 's`
Remove mention of SYNCER_MAXDELAY and "thirty seconds", using more general terms instead. This follows a discussion with alfred, in which it became clear that I had misunderstood sched_sync(). 2000-07-19 11:47:16 +00:00			`in a number of queues.`
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`The`
			`.Nm`
			`process works through the queues`
			`in a round-robin fashion,`
			`usually processing one queue per second.`
			`For each`
			`.Xr vnode 9`
Remove mention of SYNCER_MAXDELAY and "thirty seconds", using more general terms instead. This follows a discussion with alfred, in which it became clear that I had misunderstood sched_sync(). 2000-07-19 11:47:16 +00:00			`on that queue,`
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`the`
			`.Nm`
			`process forces a write out to disk of its dirty buffers.`
Include a comment explaining the usual delay between writes and syncs. 2000-07-20 07:31:52 +00:00			`.Pp`
			`Usually,`
			`buffers will be written out no more than`
			`about 30 seconds`
			`after they are dirtied.`
Added a update(4) man page to describe the kernel initiated update process and changed all of the old references to update(8) to update(4). 1996-02-12 00:45:47 +00:00			`.Sh SEE ALSO`
			`.Xr sync 2 ,`
			`.Xr fsck 8 ,`
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`.Xr sync 8`
Added a update(4) man page to describe the kernel initiated update process and changed all of the old references to update(8) to update(4). 1996-02-12 00:45:47 +00:00			`.Sh HISTORY`
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`The`
			`.Nm`
			`process is a descendant of the`
			`.Sq update`
			`command, which apeared in`
Added a update(4) man page to describe the kernel initiated update process and changed all of the old references to update(8) to update(4). 1996-02-12 00:45:47 +00:00			`.At v6 ,`
mdoc(7)'fy 1999-10-30 15:12:25 +00:00			`and was usually started by`
			`.Pa /etc/rc`
			`when the system went multi-user.`
Document the new ".Fx" macro in the mdoc man pages. I also changed the update(4) man page to use this new macro just to have something to test it on. 1996-02-12 19:27:32 +00:00			`A kernel initiated`
Replace the obsolete update(4) manual page with syncer(4). I was not abble to solicit review from <freebsd-hackers>. 2000-07-19 07:15:32 +00:00			`update`
Document the new ".Fx" macro in the mdoc man pages. I also changed the update(4) man page to use this new macro just to have something to test it on. 1996-02-12 19:27:32 +00:00			`process first appeared in`
			`.Fx 2.0 .`
Remove mention of SYNCER_MAXDELAY and "thirty seconds", using more general terms instead. This follows a discussion with alfred, in which it became clear that I had misunderstood sched_sync(). 2000-07-19 11:47:16 +00:00			`.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 .`