Filesystem Types

Linux supports many filesystem implementations with different on-disk formats, network protocols, consistency models, features, and operational tools. The right choice depends on distribution support, workload, recovery requirements, storage topology, and administrator experience.

The Virtual Filesystem Layer

The kernel's Virtual Filesystem layer, or VFS, provides common operations such as open, read, write, rename, and permission checks. Filesystem implementations connect those operations to their own data structures and backing stores.

This lets one process access ext4, XFS, NFS, tmpfs, and procfs through a shared pathname and file-descriptor model. It does not make every filesystem feature or behavior identical: case sensitivity, locking, permissions, rename guarantees, extended attributes, and error handling can differ.

CheckWhat is the primary role of Linux VFS?

Convert every mounted filesystem into ext4 on disk. Back up every file before an application writes it. Provide common kernel file operations across filesystem implementations.

Journaling and Crash Consistency

A journaling filesystem records selected updates in a journal so it can replay or discard incomplete transactions after a crash. Journaling is primarily about restoring filesystem structural consistency more quickly than a full scan.

It does not guarantee that the latest application data survived, that multi-file application transactions are valid, or that storage hardware honored every completed write. Filesystems offer different data modes and ordering guarantees, while applications must use appropriate flush and atomic-update patterns. A journal is not a backup and does not protect against deletion, malware, or device failure.

CheckWhat does filesystem journaling primarily help recover after a crash?

Consistent filesystem metadata and recorded transactions. Every historical version of every user document. Data from a physically destroyed storage device.

Common Local Filesystems

• ext4 is a mature journaling filesystem widely supported by Linux distributions and recovery tools.
• XFS is a scalable journaling filesystem commonly chosen for large filesystems and parallel I/O workloads.
• Btrfs is a copy-on-write filesystem with checksums, subvolumes, snapshots, and integrated multi-device features.

Features require operational context. A Btrfs snapshot initially shares storage with its source and is not an independent backup when it remains on the same failing device. XFS and ext4 have different grow, shrink, repair, and tuning capabilities. Confirm support for the installed kernel, boot environment, and recovery tooling before choosing or changing a root filesystem.

CheckWhy is a Btrfs snapshot on the same device not a complete backup?

Snapshots always delete the original subvolume immediately. It shares the same storage failure domain as the original. Btrfs cannot represent more than one file.

Interoperability, Network, and Virtual Filesystems

Linux can mount interoperability formats such as FAT variants, exFAT, and NTFS, but their Unix ownership, permissions, links, and filename semantics differ. Mount options and driver implementation determine how Linux presents missing features.

Network filesystems such as NFS and SMB depend on a server and network protocol, with distinct caching and identity rules. Virtual filesystems such as tmpfs, procfs, and sysfs do not use a normal persistent disk format: tmpfs stores volatile data in memory-backed pages, while procfs and sysfs expose kernel interfaces.

CheckWhich description best fits procfs?

A Windows interchange format for removable media. A virtual filesystem exposing process and kernel interfaces. A journaling disk filesystem designed for database volumes.

Discovering Active Types

Show mounted filesystem types with:

$ findmnt -o TARGET,SOURCE,FSTYPE,OPTIONS

Alternative views include df -T for mounted space accounting, lsblk -f for block devices and detected filesystem signatures, and /proc/filesystems for types supported or known by the running kernel. These answer different questions; an unmounted filesystem will not appear in an ordinary mounted-filesystem listing.

CheckWhich command directly lists mounted targets with source, type, and options in the shown lesson?

findmnt -o TARGET,SOURCE,FSTYPE,OPTIONS lsblk -o NAME,SIZE,MODEL,SERIAL,ROTA cat /proc/filesystems | sort --unique

Use Manage Linux Partitions and Filesystems on disposable storage to compare types, mount options, and discovery views.

Summary

You can now compare filesystem categories without assuming identical semantics.

1. Relate VFS to common operations across implementations.
2. Treat journaling as crash-consistency support, not backup.
3. Compare ext4, XFS, and Btrfs by supported operations and workload.
4. Distinguish local disk, network, interoperability, and virtual filesystems.
5. Use mount and block-device tools to answer different inventory questions.