How to flush cache of hard-disk and flash-disk (or filesystem) from command line?

Question

I\'m writing a backup script which

1. Copies the data to backup disk.
2. Flushes the backup disk.
3. Performs a hash integrity check.

Answer 1

You want fsync (man section 2) function call, but if you're doing this in a script, you'll probably want to use the sync command (man section 8), which just calls sync().