SYNCER(4) MidnightBSD 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 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 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).

MidnightBSD 0.3 July 14, 2000 MidnightBSD 0.3