Fsck − The unix† File System Check Program



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TABLE OF CONTENTS
1. Introduction
2. Overview of the file system
2.1. Superblock
2.2. Summary Information. Cylinder groups. Fragments. Updates to the file system
3. Fixing corrupted file systems
3.1. Detecting and correcting corruption. Super block checking. Free block checking. Checking the inode state. Inode links. Inode data size. Checking the data associated with an inode
3.8. File system connectivity
Acknowledgements
References
4. Appendix A
4.1. Conventions. Initialization. Phase 1 - Check Blocks and Sizes. Phase b - Rescan for more Dups
4.5. Phase 2 - Check Pathnames
4.6. Phase 3 - Check Connectivity. Phase 4 - Check Reference Counts. Phase 5 - Check Cyl groups. Cleanup


The
UNIX
File System Check Program
SMM:3-3
1. Introduction
This document reflects the use of fsck with the BSD and BSD file system organization. This is a revision of the original paper written by T. J. Kow alski.
When a UNIX operating system is brought up, a consistency check of the file systems should always be performed. This precautionary measure helps to insure a reliable environment for file storage on disk. If an inconsistency is discovered, corrective action must betaken. Fsck runs in two modes. Normally it is run non-interactively by the system after a normal boot. When running in this mode, it will only make changes to the file system that are known to always be correct. If an unexpected inconsistency is found fsck will exit with a nonzero exit status, leaving the system running single-user. Typically the operator then runs fsck
interactively. When running in this mode, each problem is listed followed by a suggested corrective action.
The operator must decide whether or not the suggested correction should be made.
The purpose of this memo is to dispel the mystique surrounding file system inconsistencies. It first describes the updating of the file system (the calm before the storm) and then describes file system corruption (the storm. Finally, the set of deterministic corrective actions used by fsck (the Coast Guard to the rescue) is presented.


Fsck − the unix file system check program
Can’t stat fcan’t make sense out of name
Impossible minfree=
Magic number wrong
Can not read blk
Partially truncated inode
Link count table overflow (continue)
Excessive bad blks
Bad state ddd to blkerr
Partially allocated inode i=
Root inode unallocated (allocate)
Cannot allocate root inode
I out of range i=
Zero length directory i=
Directory corrupted i=
Missing ‘.’ i=
Extra ‘.’ entry i=
Missing ‘..’ i=
Extra ‘..’ entry i=
Bad state s for root inode
No lost+found directory (create)
Sorry. cannot create lost+found directory
Sorry. no space in lost+found directory
Directory f length
Unref file i=
No space left in /lost+found (expand)
Link count type i=


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