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SYNCER(4)                BSD Kernel Interfaces Manual                SYNCER(4)

NAME
     syncer -- file system synchronizer kernel process

SYNOPSIS
     syncer

DESCRIPTION
     The syncer kernel process helps protect the integrity of disk volumes by
     flushing volatile cached file system data to disk.

     The kernel places all vnode(9)'s in a number of queues.  The syncer
     process works through the queues in a round-robin fashion, usually pro-
     cessing one queue per second.  For each vnode(9) on that queue, the
     syncer process forces a write out to disk of its dirty buffers.

     The usual delay between the time buffers are dirtied and the time they
     are synced is controlled by the following sysctl(8) tunable variables:

     Variable         Default      Description
     kern.filedelay   30           time to delay syncing files
     kern.dirdelay    29           time to delay syncing directories
     kern.metadelay   28           time to delay syncing metadata

SEE ALSO
     sync(2), fsck(8), sync(8), sysctl(8)

HISTORY
     The syncer process is a descendant of the 'update' command, which
     appeared in Version 6 AT&T UNIX, and was usually started by /etc/rc when
     the system went multi-user.  A kernel initiated 'update' process first
     appeared in FreeBSD 2.0.

BUGS
     It is possible on some systems that a sync(2) occurring simultaneously
     with a crash may cause file system damage.  See fsck(8).

BSD                              July 14, 2000                             BSD