Linux Filesystem Overview

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The Linux Filesystem: A Comprehensive Guide #

The Linux filesystem is a structured hierarchy that organizes files and directories in a predictable way. Understanding its layout, structure, and key components is crucial for system administrators, developers, and power users.

Introduction #

A filesystem in Linux determines how files are stored, accessed, and managed. It provides a logical structure to organize data efficiently.

Filesystem Hierarchy Standard (FHS) #

The Filesystem Hierarchy Standard (FHS) defines the structure of directories and files in Unix-like operating systems. It ensures consistency across distributions.

Key Directories in Linux #

/ #

The root directory, the starting point of the Linux filesystem.

/bin #

Essential user binaries (e.g., ls, cp, mv).

/boot #

Bootloader-related files (e.g., grub, vmlinuz).

/dev #

Device files (e.g., /dev/sda, /dev/null).

/etc #

System configuration files.

/home #

User home directories.

/lib, /lib64 #

Essential shared libraries.

/mnt & /media #

Mount points for external devices.

/opt #

Optional software packages.

/proc #

Virtual filesystem with system and process information.

/root #

Home directory of the root user.

/sbin #

System binaries (e.g., fsck, mount).

/tmp #

Temporary files.

/usr #

User binaries, libraries, and documentation.

/var #

Variable data (logs, caches, etc.).

Filesystem Types #

Linux supports various filesystems, each suited for different use cases:

  • ext4: Default in most distributions, journaling support.
  • XFS: High-performance, suitable for large-scale storage.
  • Btrfs: Advanced features like snapshots and subvolumes.
  • ZFS: High redundancy, self-healing.
  • tmpfs: RAM-based filesystem, used for temporary storage.
  • NFS: Network File System for sharing files over networks.

Filesystem Mounting #

To access a filesystem, it must be mounted:

# Mount a device to a directory
mount /dev/sdb1 /mnt

# Unmount a device
umount /mnt

To make mounts persistent, edit /etc/fstab:

/dev/sdb1  /mnt  ext4  defaults  0  2

Filesystem Permissions #

Linux employs a permission model:

  • Owner, Group, Others
  • Read (r), Write (w), Execute (x)
# Change file permissions
chmod 755 file.txt

# Change file ownership
chown user:group file.txt

Filesystem Management Commands #

Viewing Disk Usage #

df -h  # Show disk usage in human-readable format
du -sh /home/user  # Show directory size

Creating and Formatting Filesystems #

mkfs.ext4 /dev/sdb1  # Create an ext4 filesystem

Checking and Repairing Filesystems #

fsck /dev/sdb1  # Check and repair a filesystem

Advanced Filesystem Topics #

Logical Volume Management (LVM) #

LVM allows flexible disk management:

pvcreate /dev/sdb1
vgcreate my_vg /dev/sdb1
lvcreate -L 10G -n my_lv my_vg
mkfs.ext4 /dev/my_vg/my_lv

Filesystem Encryption #

For security, encrypt filesystems with LUKS:

cryptsetup luksFormat /dev/sdb1
cryptsetup open /dev/sdb1 my_encrypted_volume

Snapshots with Btrfs #

Btrfs supports snapshots for rollback capability:

btrfs subvolume snapshot /home /home_snapshot

Conclusion #

Understanding the Linux filesystem is essential for system administration, security, and performance tuning. Mastering filesystem operations enables better control over data management and system stability.