From LQWiki

Sync is a command used to flush the filesystem buffers (write changes still held in memory to disk). In normal operations, this is not a concern as daemons handle flushing and, during shutdown, it is usually invoked in scripts - however, it can be executed manually.

Applications

• rsync - is a sync utility based on file timestamps, not on file contents
• krusader - is a gui sync utility based on file contents
• unison - is a cli sync utility based on file contents