Use df When
You want to know whether a filesystem is full overall.
You need mount-level capacity and availability information quickly.
Compare
du vs df
When you need filesystem-level capacity information and when directory-level usage matters more.
`df` shows free and used space at the filesystem level. `du` shows how much space specific files and directories consume inside that filesystem.
Use du When
You are tracking down which directories or files are using space.
You need per-path disk usage detail to support cleanup work.
Rule of Thumb
df answers how full the filesystem is. du answers what is filling it.
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