Keywords: sag

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## Other tools for all filesystems

Some other tools are also useful for managing filesystems. `df` shows the free disk space on one or more filesystems; `du` shows how much disk space a directory and all its files contain. These can be used to hunt down disk space wasters.

`sync` forces all unwritten blocks in the buffer cache (see section 5.6) to be written to disk. It is seldom necessary to do this by hand; the daemon process `update` does this automatically. It can be useful in catastrophies, for example if `update` or its helper process `bdflush` dies, or if you must turn off power `now` and can't wait for `update` to run.