System Administration Guide: Devices and File Systems

Format and Type of Inodes

Each inode contains a mode word, which describes the type and state of the inode. Inodes might be one of nine types:

Inodes might be in one of three states:

When the file system is created, a fixed number of inodes are set aside. However, these inodes are not allocated until they are needed. An allocated inode is one that points to a file. An unallocated inode does not point to a file and, therefore, should be empty. The partially allocated state means that the inode is incorrectly formatted. An inode can get into this state if, for example, bad data is written into the inode list because of a hardware failure. The only corrective action the fsck command can take is to clear the inode.