bionic (4) syncer.4freebsd.gz

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).