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 eight types:

• Regular

• Directory

• Block special

• Character special

• FIFO (named-pipe)

• Symbolic link

• Shadow (used for ACLs)

• Socket

Inodes might be in one of three states:

• Allocated

• Unallocated

• Partially allocated

When the file system is created, a fixed number of inodes are set aside, but they 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 fsck can take is to clear the inode.