sync writes any data buffered in memory out to disk. This can
include (but is not limited to) modified superblocks, modified inodes,
and delayed reads and writes. This must be implemented by the kernel;
The sync program does nothing but exercise the sync system
call.
The kernel keeps data in memory to avoid doing (relatively slow) disk reads and writes. This improves performance, but if the computer crashes, data may be lost or the file system corrupted as a result. The sync command ensures everything in memory is written to disk.
Any arguments are ignored, except for a lone --help or --version (see Common options).
An exit status of zero indicates success, and a nonzero value indicates failure.