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.