freebsd man page for sync

SYNC(8) 						    BSD System Manager's Manual 						   SYNC(8)

NAME
     sync -- force completion of pending disk writes (flush cache)

SYNOPSIS
     sync

DESCRIPTION
     The sync utility can be called to ensure that all disk writes have been completed before the processor is halted in a way not suitably done
     by reboot(8) or halt(8).  Generally, it is preferable to use reboot(8) or halt(8) to shut down the system, as they may perform additional
     actions such as resynchronizing the hardware clock and flushing internal caches before performing a final sync.

     The sync utility utilizes the sync(2) function call.

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

HISTORY
     A sync utility appeared in Version 4 AT&T UNIX.

BSD
								   May 31, 1993 							       BSD