sync - update super-block
Sync causes all information in core memory that should be on disk to be
written out. This includes modified super blocks, modified i-nodes,
and delayed block I/O.
Sync should be used by programs which examine a file system, for exam-
ple fsck, df, etc. Sync is mandatory before a boot.
fsync(2), sync(8), update(8)
The writing, although scheduled, is not necessarily complete upon
return from sync.
4th Berkeley Distribution 12 February 1983 SYNC(2)