freebsd man page for sync

SYNC(2) 						      BSD System Calls Manual							   SYNC(2)

NAME
     sync -- schedule file system updates

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     void
     sync(void);

DESCRIPTION
     The sync() system call forces a write of dirty (modified) buffers in the block buffer cache out to disk.  The kernel keeps this information
     in core to reduce the number of disk I/O transfers required by the system.  As information in the cache is lost after a system crash, a
     sync() system call is issued frequently by the kernel process syncer(4) (about every 30 seconds).

     The fsync(2) system call may be used to synchronize individual file descriptor attributes.

SEE ALSO
     fsync(2), syncer(4), sync(8)

HISTORY
     The sync() function appeared in Version 6 AT&T UNIX.

BUGS
     The sync() system call may return before the buffers are completely flushed.

BSD
								   June 4, 1993 							       BSD