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. |