Disk usage with du and ncdu

du (disk usage) is the standard Linux command that reports how much space files and directories use; ncdu is an interactive, ncurses-based alternative that lets you browse the results and delete items. Together with df, which shows free space per file system, they are the usual way to find what fills a disk.

1Useful du options

du -sh /var prints one human-readable total. du -h --max-depth=1 / lists the size of each top-level directory. -x stays on one file system, so mounted disks and /proc are skipped.

Piping to sort finds the biggest items: du -xh --max-depth=1 / | sort -h.

2ncdu

ncdu -x / scans the root file system and opens a browsable list sorted by size. Arrow keys move, Enter opens a folder, 'd' deletes the selected item after confirmation, 'q' quits. ncdu is usually installed from the distribution's package (for example apt install ncdu).

3When du and df disagree

If df reports a full disk but du finds less, a deleted file may still be held open by a running process. The space returns when that process closes the file or restarts.

How to find what fills the disk

1. See which file system is full: df -h
2. List the biggest top-level folders: sudo du -xh --max-depth=1 / | sort -h
3. Go one level deeper into the largest folder and repeat.
4. Or browse interactively: sudo ncdu -x /

Related articles

• df (disk free)How to read df output, why Use% can reach 100% before Avail is zero for normal users, and how to check inodes with df -i.
• Inodes and 'No space left on device'What an inode is, how to see inode usage with df -i, and how to find directories with millions of small files.
• Finding large and old files with findHow to use find to list big or old files on Linux, preview them safely and delete only what you checked.

Sources

1. du(1) man7.org
2. ncdu(1) (Debian) manpages.debian.org
3. df(1) man7.org

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Last reviewed: 2026-10-08