sync

sync flushes cached writes to persistent storage.

sync [options] [file...]

$ sync

When a program writes to a file, the data does not always reach the physical device immediately — for speed, the system holds recent writes in memory and writes them out a little later. sync forces that pending data out now, so that what is on the device matches what programs have written.

It is the command to run before doing something that should not lose recent writes — before powering off by hand, or before removing storage.

Options #

With no argument, sync flushes everything. The options narrow it:

Exit status #

sync returns 0, or 1 if a named file could not be reached.