sync —
force completion of pending disk writes (flush cache)
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.
sync utilizes the
sync(2) function.
A sync command appeared in
Version 4 AT&T UNIX.