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.. 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.
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