SYNC(2) System Calls Manual SYNC(2)
sync - update super-block
sync() writes out all information in core memory that should be on
disk. This includes modified super blocks, modified inodes, and
delayed block I/O.
sync() should be used by programs that examine a file system, for exam-
ple fsck(8), df(1V), etc. sync() is mandatory before a boot.
The writing, although scheduled, is not necessarily complete upon
return from sync().
21 January 1990 SYNC(2)