dosfs filesystem components checked by fsck
The following two components are checked:
-
File Allocation Table (FAT)
-
directory entries
dosfs-fsck phase 1: check FATs
Every dosfs filesystem maintains two or more identical copies of the
File Allocation Table (FAT).
During Phase 1, fsck performs two types of checks:
-
The FATs are checked first for readability.
At least one FAT must be readable for fsck to proceed.
-
All readable FATs are checked to see if they are in sync.
If FATs are in sync,
Phase 2 occurs.
dosfs-fsck phase 2: check directory entries (pass 1)
During Phase 2, fsck performs the following checking:
-
If the entry is for ``..'', check that the start cluster
matches the one for the parent directory.
-
If the entry is for ``.'', check that the start cluster
matches the one for the current directory.
-
If the entry is for a directory, check that file size is zero.
-
If the entry is for a file, check that the file size is set
to the correct byte count.
-
For each directory entry check that:
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its start cluster number is within range
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all its FAT entries are within range
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If the entry is for a long name, then check the
sequence number.
Also check for the presence of an associated alias
name entry.
The following information is collected during Phase 2:
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number of subdirectories
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number of regular files
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number of hidden files
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byte count per subdirectories
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byte count per regular files
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byte count per hidden files
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for each cluster in the filesystem, number of times it is
being claimed. This information is used during cross referencing checking.
dosfs-fsck phase 3: cross reference check
During Phase 3, fsck will perform the following checking:
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allocation units (clusters) claimed by more than one directory entry
-
lost clusters (clusters not claimed by any directory entry
but still marked FREE in the FAT)
dosfs-fsck phase 4: check directory entries (pass 2)
Phase 4 is the same as Phase 2. It is only needed and performed by fsck
if there was a corrective action performed during cross-referencing checking
that had invalidated the data collected during Phase 2.
dosfs-fsck phase 4: check boot area (FAT 32 only)
-
Check location of backup boot sector.
-
Check location and contents of FS info sector.
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fsck_dosfs - user interface
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Sample fsck_dosfs command use
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SCO OpenServer Release 6.0.0 -- 05 June 2007