5.10.12. 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. Both have manual pages which detail the (many) options which can be used.
sync forces all unwritten blocks in the buffer cache (see Section 6.6 ) 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 catastrophes, 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. Again, there are manual pages. The man is your very best friend in Linux. Its cousin apropos is also very useful when you don't know what the name of the command you want is.
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