fsdb —
FFS debugging/editing tool
fsdb opens fsname (usually a raw
  disk partition) and runs a command loop allowing manipulation of the file
  system's inode data. You are prompted to enter a command with “fsdb
  (inum X)>” where X is the currently selected
  i-number. The initial selected inode is the root of the filesystem (i-number
  2). The command processor uses the
  editline(3) library, so you
  can use command line editing to reduce typing if desired. When you exit the
  command loop, the file system superblock is marked dirty and any buffered
  blocks are written to the file system.
The -d option enables additional debugging
    output (which comes primarily from
    fsck(8)-derived code).
The -F option indicates that
    filesystem is a file system image, rather than a raw
    character device. It will be accessed ‘as-is’, and no attempts
    will be made to read a disklabel.
The -n option disables writing to the
    device, preventing any changes from being made to the filesystem.
Besides the built-in editline(3)
  commands, fsdb supports these commands:
  - help
- Print out the list of accepted commands.
    
  
- inodei-number
- Select inode i-number as the new current inode.
    
  
- back
- Revert to the previously current inode.
    
  
- clrii-number
- Clear the inode i-number.
    
  
- lookupname
-  
- cdname
- Find name in the current directory and make its
      inode the current inode. Name may be a
      multi-component name or may begin with slash to indicate that the root
      inode should be used to start the lookup. If some component along the
      pathname is not found, the last valid directory encountered is left as the
      active inode.
    
 This command is valid only if the starting inode is a directory.
- active
-  
- print
- Print out the active inode.
    
  
- uplink
- Increment the active inode's link count.
    
  
- downlink
- Decrement the active inode's link count.
    
  
- linkcountnumber
- Set the active inode's link count to number.
    
  
- ls
- List the current inode's directory entries. This command is valid only if
      the current inode is a directory.
    
  
- blks
- List the current inode's blocks numbers.
    
  
- findblkdisk block number ...
- Find the inode(s) owning the specified disk block(s) number(s). Note that
      these are not absolute disk blocks numbers, but offsets from the start of
      the partition.
    
  
- saveblksfilename
- Save the current inode's data into filename.
    
  
- rmname
-  
- delname
- Remove the entry name from the current directory
      inode. This command is valid only if the current inode is a directory.
    
  
- lnino name
- Create a link to inode ino under the name
      name in the current directory inode. This command is
      valid only if the current inode is a directory.
    
  
- chinumdirslot inum
- Change the i-number in directory entry dirslot to
      inum.
    
  
- chnamedirslot name
- Change the name in directory entry dirslot to
      name. This command cannot expand a directory entry.
      You can only rename an entry if the name will fit into the existing
      directory slot.
    
  
- chtypetype
- Change the type of the current inode to type.
      type may be one of: file,
      dir, socket, or
      fifo.
    
  
- chmodmode
- Change the mode bits of the current inode to mode.
      You cannot change the file type with this subcommand; use
      chtypeto do that.
- chflagsflags
- Change the file flags of the current inode to flags.
    
  
- chownuid
- Change the owner of the current inode to uid.
    
  
- chgrpgid
- Change the group of the current inode to gid.
    
  
- chgengen
- Change the generation number of the current inode to
      gen.
    
  
- mtimetime
-  
- ctimetime
-  
- atimetime
- Change the modification, change, or access time (respectively) on the
      current inode to time. Time
      should be in the format YYYYMMDDHHMMSS[.nsec] where
      nsec is an optional nanosecond specification. If no
      nanoseconds are specified, the mtimensec,
      ctimensec, or atimensec field
      will be set to zero.
    
  
- quit,- q,- exit,
    ⟨EOF⟩
- Exit the program.
fsdb uses the source code for
  fsck(8) to implement most of the
  file system manipulation code. The remainder of fsdb
  first appeared in NetBSD 1.1.
Use this tool with extreme caution -- you can damage an FFS file system beyond
  what fsck(8) can repair.
Manipulation of “short” symlinks doesn't work (in particular,
  don't try changing a symlink's type).
You must specify modes as numbers rather than symbolic names.
There are a bunch of other things that you might want to do which
  fsdb doesn't implement.