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Linux File Systems

Linux file systems organize stored data as files and directories, record metadata such as ownership and timestamps, and connect storage to one shared directory tree. Linux uses a common virtual interface so local, network, memory-backed, and user-space file systems can serve the same file operations.

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Don't Panic — Linux File Systems

A file system is Linux's way of turning storage, a remote service, or live kernel data into names and directories. Before this arrangement, each program would need its own map of disks and data layouts, which is a reliable route to paperwork with sharp edges. Instead, a path such as `/var/lib/app/state.db` can lead through one shared-looking tree while the machinery underneath changes completely.

The helpful clerk at the center is the VFS, the virtual file-system layer. It gives applications familiar operations such as open, read, write, and rename. Behind that calm desk, ext4, XFS, Btrfs, NFS, CephFS, FUSE, and proc take rather different routes. The shared verbs do not promise shared behavior for allocation, caching, recovery, or failure. That is the first useful suspicion to keep.

A mount attaches one hierarchy to a directory in a process's visible tree. This is why Linux can present many file systems as one place, and why the same spelling of a path can mean something different inside another mount namespace. The other surprise is that a name is not the object. A directory entry points at an inode, an inode carries metadata and data mapping, and an open file can remain alive after its last name vanishes. Files have a quiet afterlife, because apparently naming them was only part of the relationship.

Space reports also answer different questions. `df` asks the mounted file system about its accounting. `du` adds up reachable names. A mismatch is therefore a clue about snapshots, metadata, sparse allocation, or an open deleted file, not an automatic verdict that either command has lost the plot. Byte capacity and inode capacity are separate limits, so creating one more tiny file can fail while a large-looking amount of storage remains.

For the map of names, mounts, VFS objects, and durability, read the Introduction and Slides. Use the Cheatsheet when you need the comparison tables and failure-triage order. The Practice tab turns one temporary path into observable mount, inode, and capacity evidence. Field Notes covers the operational decisions that make a correct command output useful instead of merely decorative.

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