sync - update the super block
Sync executes the sync system primitive. Sync can be called to insure
all disk writes have been completed before the processor is halted in a
way not suitably done by reboot(8) or halt(8).
See sync(2) for details on the system primitive.
sync(2), fsync(2), halt(8), reboot(8), update(8)
4th Berkeley Distribution 4 February 1983 SYNC(8)