NAME
syncer —
file system synchronizer kernel
process
SYNOPSIS
syncer |
DESCRIPTION
Thesyncer 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
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).