linux/Documentation/filesystems/ext4/special_inodes.rst
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   1.. SPDX-License-Identifier: GPL-2.0
   2
   3Special inodes
   4--------------
   5
   6ext4 reserves some inode for special features, as follows:
   7
   8.. list-table::
   9   :widths: 6 70
  10   :header-rows: 1
  11
  12   * - inode Number
  13     - Purpose
  14   * - 0
  15     - Doesn't exist; there is no inode 0.
  16   * - 1
  17     - List of defective blocks.
  18   * - 2
  19     - Root directory.
  20   * - 3
  21     - User quota.
  22   * - 4
  23     - Group quota.
  24   * - 5
  25     - Boot loader.
  26   * - 6
  27     - Undelete directory.
  28   * - 7
  29     - Reserved group descriptors inode. (“resize inode”)
  30   * - 8
  31     - Journal inode.
  32   * - 9
  33     - The “exclude” inode, for snapshots(?)
  34   * - 10
  35     - Replica inode, used for some non-upstream feature?
  36   * - 11
  37     - Traditional first non-reserved inode. Usually this is the lost+found directory. See s\_first\_ino in the superblock.
  38
  39Note that there are also some inodes allocated from non-reserved inode numbers
  40for other filesystem features which are not referenced from standard directory
  41hierarchy. These are generally reference from the superblock. They are:
  42
  43.. list-table::
  44   :widths: 20 50
  45   :header-rows: 1
  46
  47   * - Superblock field
  48     - Description
  49
  50   * - s\_lpf\_ino
  51     - Inode number of lost+found directory.
  52   * - s\_prj\_quota\_inum
  53     - Inode number of quota file tracking project quotas
  54   * - s\_orphan\_file\_inum
  55     - Inode number of file tracking orphan inodes.
  56