Glossary · Operating Systems & Software

ext4

ext4 is the fourth extended file system, the long-standing default on many Linux distributions, offering journaling, large volumes, and good reliability.

Updated October 6, 2026

ext4 is a journaling file system for Linux, the successor to ext3. It supports volumes up to 1 exbibyte and files up to 16 tebibytes, and it is the default on many distributions.

Why it matters

ext4 is a safe, well-tested choice for web servers and general Linux disks. Its journal keeps the file system consistent after an unclean shutdown, and tools like fsck can check and repair it. It uses Unix-style ownership and permissions.

Other options such as XFS, Btrfs, and ZFS add features like snapshots.

Example

$ sudo mkfs.ext4 /dev/sdb1
$ sudo mount /dev/sdb1 /var/www
$ df -i /var/www

The last command shows inode usage. A disk can report free space yet fail to create files if it runs out of inodes.

Common mistakes

  • Formatting the wrong device; confirm with lsblk before running mkfs.
  • Ignoring inode exhaustion on directories holding millions of small files.
  • Running fsck on a mounted file system.

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