---
name: "syncer"
section: "4"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/syncer"
---

# syncer(4)

file system synchronizer kernel process

## 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)](/vnode/9.md)'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)](/vnode/9.md) 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)](/sysctl/8.md) 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)](/sync/2.md), [fsck(8)](/fsck/8.md), [sync(8)](/sync/8.md), [sysctl(8)](/sysctl/8.md)

## 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)](/sync/2.md) occurring simultaneously with a crash may cause file system damage. See [fsck(8)](/fsck/8.md).