sync - update super block
The sync() function writes all information in memory that
should be on disk, including modified super blocks, modified
inodes, and delayed block I/O.
Unlike fsync(3C), which completes the writing before it
returns, sync() schedules but does not necessarily complete
the writing before returning.
The sync() function should be used by applications that
examine a file system, such as fsck(1M), and df(1M), and is
mandatory before rebooting.
df(1M), fsck(1M), fsync(3C)
Man(1) output converted with