Silicon Graphics IRIS Workstation User Manual page 55

IRIS WORKSTATION GUIDE 51
Appendix B:
within the file system. If they don't agree, then fsck may replace the count in
the super-block by the actual free-block count.
Free-Inode Count.
The super-block contains a count of the total number of free inodes within
the file system. Fsck compares this count to the number of inodes it found free
within the file system. If they don't agree, then fsck may replace the count in
the super-block by the actual free-inode count.
Inodes
An individual inode is not as likely to be corrupted as the super-block.
However, because of the great number of active inodes, there is almost as
likely a chance for corruption in the inode list as in the super-block.
The list of inodes is checked sequentially starting with inode 1 (there is no
inode 0) and going to the last inode in the file system. Each inode can be
checked for inconsistencies involving format and type, link count, duplicate
blocks, bad blocks, and inode size.
Format and Type.
Each inode contains a mode word. This mode word describes the type and
state of the inode. Inodes may be one of four types: regular inode, directory
inode, special block inode, and special character inode. If an inode is not one
of these types, then the inode has an illegal type. Inodes may be found in one
of three states: unallocated, allocated, and neither unallocated nor allocated.
This last state indicates an incorrectly formatted inode. An inode can get in
this state if bad data is written into the inode list through, for example, a
hardware failure. The only possible corrective action is for fsck is to clear the
inode.
Link Count.
Contained in each inode is a count of the total number of directory entries
linked to the inode.
Fsck verifies the link count of each inode by traversing down the total directory
structure, starting from the root directory, calculating an actual link count for
each inode.
If the stored link count is non-zero and the actual link count is zero, it means
that no directory entry appears for the inode. If the stored and actual link
counts are non-zero and unequal, a directory entry may have been added or
removed without the inode being updated.
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