1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)sync.2 8.1 (Berkeley) 06/04/93 7.\" 8.Dd 9.Dt SYNC 2 10.Os BSD 4 11.Sh NAME 12.Nm sync 13.Nd "synchronize disk block in-core status with that on disk" 14.Sh SYNOPSIS 15.Fd #include <unistd.h> 16.Ft void 17.Fn sync void 18.Sh DESCRIPTION 19The 20.Fn sync 21function forces a write of dirty (modified) buffers 22in the block buffer cache out 23to disk. The kernel keeps this information in core to reduce 24the number of disk I/O transfers required by the system. 25As information in the cache is lost after a system crash a 26.Fn sync 27call is issued 28frequently 29by the user process 30.Xr update 8 31(about every 30 seconds). 32.Pp 33The function 34.Xr fsync 2 35may be used to synchronize individual file descriptor 36attributes. 37.Sh SEE ALSO 38.Xr fsync 2 , 39.Xr sync 8 , 40.Xr update 8 41.Sh BUGS 42.Fn Sync 43may return before the buffers are completely flushed. 44.Sh HISTORY 45A 46.Nm 47function call appeared in Version 6 AT&T UNIX. 48