NAME¶
syncer —
file system synchronizer
kernel process
SYNOPSIS¶
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).
