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$FreeBSD: head/share/man/man4/syncer.4 63647 2000-07-20 13:05:41Z sheldonh $
.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.
p 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.
p 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 appeared in .At v6 , and was usually started by
a /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 .