Special inodes¶
ext4 reserves some inode for special features, as follows:
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:
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. |