Filesystem

Everything in Linux is reachable through a single directory tree, no matter how many physical or virtual disks back it. This section covers how that tree is built and controlled.

• ACLs and Extended Attributes

  Standard permissions grant exactly one owner, one group, and "everyone else" - ACLs extend that to arbitrary additional users and groups on a single file, while extended attributes attach arbitrary metadata, including the immutable bit that overrides permissions entirely.

• Disk Partitioning

  Dividing a physical or virtual disk into separate logical sections before a filesystem can be created on any of them - and the two competing partition table formats you'll run into.

• Disk Usage Analysis

  Finding what's actually consuming disk space and inodes when a filesystem fills up - du and ncdu for locating large directories, and the specific case where df and du disagree because a deleted file is still open.

• File Permissions and Ownership

  How Linux represents ownership and permission bits, and how to read and change them.

• Filesystem Types

  The on-disk format that determines how data is stored and retrieved, and why different Linux distributions default to different ones.

• Links: Hard vs. Symbolic

  Two different ways for one file to be reachable from multiple paths - a hard link shares the same underlying data, a symbolic link is just a pointer to a path.

• LVM Basics

  Logical Volume Manager adds a flexible layer between raw partitions and filesystems - volumes that can be resized, spanned across multiple disks, and snapshotted, without being locked into fixed partition boundaries.

• Mounting and fstab

  How a filesystem on a disk, partition, or network share gets attached into the single Linux directory tree, and how /etc/fstab makes that attachment happen automatically at boot.

• RAID Basics

  RAID combines multiple physical disks into one logical unit for redundancy, performance, or both - mdadm is the standard Linux software implementation, distinct from LVM's volume-spanning, which offers no redundancy on its own.