Special inodes

.. SPDX-License-Identifier: GPL-2.0

Special inodes

ext4 reserves some inode for special features, as follows:

.. list-table:: :widths: 6 70 :header-rows: 1

• • inode Number
  • Purpose
• • 0
  • Doesn't exist; there is no inode 0.
• • 1
  • List of defective blocks.
• • 2
  • Root directory.
• • 3
  • User quota.
• • 4
  • Group quota.
• • 5
  • Boot loader.
• • 6
  • Undelete directory.
• • 7
  • Reserved group descriptors inode. (“resize inode”)
• • 8
  • Journal inode.
• • 9
  • The “exclude” inode, for snapshots(?)
• • 10
  • Replica inode, used for some non-upstream feature?
• • 11
  • Traditional first non-reserved inode. Usually this is the lost+found directory. See s_first_ino in the superblock.

Note that there are also some inodes allocated from non-reserved inode numbers for other filesystem features which are not referenced from standard directory hierarchy. These are generally reference from the superblock. They are:

.. list-table:: :widths: 20 50 :header-rows: 1

• • Superblock field
  • Description
• • s_lpf_ino
  • Inode number of lost+found directory.
• • s_prj_quota_inum
  • Inode number of quota file tracking project quotas
• • s_orphan_file_inum
  • Inode number of file tracking orphan inodes.