0001 .. SPDX-License-Identifier: GPL-2.0
0002
0003 Special inodes
0004 --------------
0005
0006 ext4 reserves some inode for special features, as follows:
0007
0008 .. list-table::
0009 :widths: 6 70
0010 :header-rows: 1
0011
0012 * - inode Number
0013 - Purpose
0014 * - 0
0015 - Doesn't exist; there is no inode 0.
0016 * - 1
0017 - List of defective blocks.
0018 * - 2
0019 - Root directory.
0020 * - 3
0021 - User quota.
0022 * - 4
0023 - Group quota.
0024 * - 5
0025 - Boot loader.
0026 * - 6
0027 - Undelete directory.
0028 * - 7
0029 - Reserved group descriptors inode. (“resize inode”)
0030 * - 8
0031 - Journal inode.
0032 * - 9
0033 - The “exclude” inode, for snapshots(?)
0034 * - 10
0035 - Replica inode, used for some non-upstream feature?
0036 * - 11
0037 - Traditional first non-reserved inode. Usually this is the lost+found directory. See s_first_ino in the superblock.
0038
0039 Note that there are also some inodes allocated from non-reserved inode numbers
0040 for other filesystem features which are not referenced from standard directory
0041 hierarchy. These are generally reference from the superblock. They are:
0042
0043 .. list-table::
0044 :widths: 20 50
0045 :header-rows: 1
0046
0047 * - Superblock field
0048 - Description
0049
0050 * - s_lpf_ino
0051 - Inode number of lost+found directory.
0052 * - s_prj_quota_inum
0053 - Inode number of quota file tracking project quotas
0054 * - s_orphan_file_inum
0055 - Inode number of file tracking orphan inodes.
