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Man Pages


Manual Reference Pages  -  SYNCER (4)

NAME

syncer - file system synchronizer kernel process

CONTENTS

Synopsis
Description
See Also
History
Bugs

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 processing 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 AT&T v6 , and was usually started by /etc/rc when the system went multi-user. A kernel initiated 'update' process first appeared in
.Fx 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).
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