SYNCER(4FREEBSD) - Linux man page online | Special files

File system synchronizer kernel process.

July 14, 2000
SYNCER(4) BSD Kernel Interfaces Manual SYNCER(4)


syncer — file system synchronizer kernel process




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 con‐ trolled 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


sync(2), fsck(8), sync(8), sysctl(8)


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 initi‐ ated ‘update’ process first appeared in FreeBSD 2.0.


It is possible on some systems that a sync(2) occurring simultaneously with a crash may cause file system damage. See fsck(8).
BSD July 14, 2000 BSD
This manual Reference Other manuals
syncer(4freebsd) referred by fdatasync(2freebsd) | fsync(2freebsd) | sync(2freebsd)
refer to fsck(8) | sync(2) | sysctl(8) | vnode(9freebsd)
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