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 |
