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DEBUGFS(8)		    System Manager's Manual		    DEBUGFS(8)



NAME
       debugfs - ext2/ext3/ext4 file system debugger

SYNOPSIS
       debugfs [ -DVwci ] [ -b blocksize ] [ -s superblock ] [ -f cmd_file ] [
       -R request ] [ -d data_source_device ] [ device ]

DESCRIPTION
       The debugfs program is an interactive file system debugger. It  can  be
       used  to	 examine  and  change the state of an ext2, ext3, or ext4 file
       system.
       device is the special file corresponding to the device  containing  the
       file system (e.g /dev/hdXX).

OPTIONS
       -w     Specifies	 that  the  file system should be opened in read-write
	      mode.  Without this option, the file system is opened  in	 read-
	      only mode.

       -c     Specifies	 that the file system should be opened in catastrophic
	      mode, in which the inode and group bitmaps  are  not  read  ini-
	      tially.	This  can  be  useful for filesystems with significant
	      corruption, but because of this, catastrophic  mode  forces  the
	      filesystem to be opened read-only.

       -i     Specifies	 that  device represents an ext2 image file created by
	      the e2image program.  Since the ext2 image  file	only  contains
	      the  superblock, block group descriptor, block and inode alloca-
	      tion bitmaps, and the inode table, many  debugfs	commands  will
	      not  function properly.  Warning: no safety checks are in place,
	      and debugfs may fail in interesting ways if commands such as ls,
	      dump,  etc.  are tried without specifying the data_source_device
	      using the -d option.  debugfs is a debugging tool.  It has rough
	      edges!

       -d data_source_device
	      Used  with  the  -i  option,  specifies  that data_source_device
	      should be used when reading blocks not found in the  ext2	 image
	      file.  This includes data, directory, and indirect blocks.

       -b blocksize
	      Forces  the  use	of  the	 given block size for the file system,
	      rather than detecting the correct block size as normal.

       -s superblock
	      Causes the file system superblock to  be	read  from  the	 given
	      block  number,  instead of using the primary superblock (located
	      at an offset of 1024 bytes from the beginning  of	 the  filesys-
	      tem).   If  you specify the -s option, you must also provide the
	      blocksize of the filesystem via the -b option.

       -f cmd_file
	      Causes debugfs to read in commands from  cmd_file,  and  execute
	      them.   When  debugfs  is	 finished executing those commands, it
	      will exit.

       -D     Causes debugfs to open the device using  Direct  I/O,  bypassing
	      the  buffer cache.  Note that some Linux devices, notably device
	      mapper as of this writing, do not support Direct I/O.

       -R request
	      Causes debugfs to execute the single command request,  and  then
	      exit.

       -V     print the version number of debugfs and exit.

SPECIFYING FILES
       Many  debugfs  commands	take  a	 filespec as an argument to specify an
       inode (as opposed to a pathname) in the filesystem which	 is  currently
       opened  by  debugfs.   The  filespec  argument  may be specified in two
       forms.  The first form is an inode number surrounded by angle brackets,
       e.g.,  <2>.  The second form is a pathname; if the pathname is prefixed
       by a forward slash ('/'), then it is interpreted relative to  the  root
       of  the	filesystem  which is currently opened by debugfs.  If not, the
       pathname is interpreted relative to the current	working	 directory  as
       maintained  by debugfs.	This may be modified by using the debugfs com-
       mand cd.

COMMANDS
       This is a list of the commands which debugfs supports.

       blocks filespace
	      Print the blocks used by the inode filespec to stdout.

       bmap filespec logical_block
	      Print the physical block number  corresponding  to  the  logical
	      block number logical_block in the inode filespec.

       block_dump [-f filespec] block_num
	      Dump  the	 filesystem  block given by block_num in hex and ASCII
	      format to the console.  If the -f option is specified, the block
	      number is relative to the start of the given filespec.

       cat filespec
	      Dump the contents of the inode filespec to stdout.

       cd filespec
	      Change the current working directory to filespec.

       chroot filespec
	      Change the root directory to be the directory filespec.

       close [-a]
	      Close the currently open file system.  If the -a option is spec-
	      ified, write out any changes to the superblock and  block	 group
	      descriptors  to  all  of the backup superblocks, not just to the
	      master superblock.

       clri filespec
	      Clear the contents of the inode filespec.

       dirsearch filespec filename
	      Search the directory filespec for filename.

       dirty  Mark the filesystem as dirty, so that the	 superblocks  will  be
	      written on exit.

       dump [-p] filespec out_file
	      Dump  the	 contents  of  the  inode  filespec to the output file
	      out_file.	 If the -p option is given set the  owner,  group  and
	      permissions information on out_file to match filespec.

       dump_mmp
	      Display the multiple-mount protection (mmp) field values.

       dx_hash [-h hash_alg] [-s hash_seed] filename
	      Calculate	 the  directory	 hash of filename.  The hash algorithm
	      specified with -h may be legacy, half_md4,  or  tea.   The  hash
	      seed specified with -s must be in UUID format.

       dump_extents [-n] [-l] filespec
	      Dump  the	 the  extent  tree of the inode filespec.  The -n flag
	      will cause dump_extents to only display the  interior  nodes  in
	      the  extent  tree.   The -l flag will cause dump_extents to only
	      display the leaf nodes in the extent tree.

	      (Please note that the length and range of blocks	for  the  last
	      extent in an interior node is an estimate by the extents library
	      functions, and is not  stored  in	 filesystem  data  structures.
	      Hence,  the values displayed may not necessarily by accurate and
	      does not indicate a problem or corruption in the file system.)

       expand_dir filespec
	      Expand the directory filespec.

       feature [fs_feature] [-fs_feature] ...
	      Set or clear various  filesystem	features  in  the  superblock.
	      After  setting  or  clearing  any	 filesystem features that were
	      requested, print the current state  of  the  filesystem  feature
	      set.

       filefrag [-dvr] filespec
	      Print the number of contiguous extents in filespec.  If filespec
	      is a directory and the -d option is not specified, filefrag will
	      print  the  number  of  contiguous  extents for each file in the
	      directory.  The -v option will cause filefrag  print  a  tabular
	      listing  of  the	contiguous extents in the file.	 The -r option
	      will cause filefrag to do a recursive listing of the directory.

       find_free_block [count [goal]]
	      Find the first count free blocks, starting from goal  and	 allo-
	      cate it.	Also available as ffb.

       find_free_inode [dir [mode]]
	      Find  a  free  inode and allocate it.  If present, dir specifies
	      the inode number of the directory	 which	the  inode  is	to  be
	      located.	 The  second optional argument mode specifies the per-
	      missions of the new inode.  (If the directory bit is set on  the
	      mode,  the  allocation routine will function differently.)  Also
	      available as ffi.

       freeb block [count]
	      Mark the block number block as not allocated.  If	 the  optional
	      argument	count  is present, then count blocks starting at block
	      number block will be marked as not allocated.

       freefrag [-c chunk_kb]
	      Report free space fragmentation on the currently open file  sys-
	      tem.   If	 the  -c option is specified then the filefrag command
	      will print how many free chunks of size chunk_kb can be found in
	      the  file	 system.  The chunk size must be a power of two and be
	      larger than the file system block size.

       freei filespec [num]
	      Free the inode specified by filespec.  If num is specified, also
	      clear num-1 inodes after the specified inode.

       help   Print a list of commands understood by debugfs.

       htree_dump filespec
	      Dump  the	 hash-indexed  directory  filespec,  showing  its tree
	      structure.

       icheck block ...
	      Print a listing of the inodes which use the one or  more	blocks
	      specified on the command line.

       inode_dump filespec
	      Print  the contents of the inode data structure in hex and ASCII
	      format.

       imap filespec
	      Print the location of the inode data structure (in the inode ta-
	      ble) of the inode filespec.

       init_filesys device blocksize
	      Create an ext2 file system on device with device size blocksize.
	      Note that this does not fully initialize all of the data	struc-
	      tures;  to  do  this, use the mke2fs(8) program.	This is just a
	      call to the low-level library, which sets up the superblock  and
	      block descriptors.

       kill_file filespec
	      Deallocate  the  inode  filespec and its blocks.	Note that this
	      does not remove any directory entries (if any)  to  this	inode.
	      See the rm(1) command if you wish to unlink a file.

       lcd directory
	      Change  the  current working directory of the debugfs process to
	      directory on the native filesystem.

       ln filespec dest_file
	      Create a link named dest_file which is a hard link to  filespec.
	      Note this does not adjust the inode reference counts.

       logdump [-acs] [-b block] [-i filespec] [-f journal_file] [output_file]
	      Dump  the	 contents  of  the ext3 journal.  By default, dump the
	      journal inode as specified in the superblock.  However, this can
	      be  overridden  with the -i option, which dumps the journal from
	      the internal inode given by filespec.  A regular file containing
	      journal data can be specified using the -f option.  Finally, the
	      -s option utilizes the backup information in the	superblock  to
	      locate the journal.

	      The  -a  option causes the logdump program to print the contents
	      of all of the descriptor blocks.	The -b option  causes  logdump
	      to  print	 all  journal  records that are refer to the specified
	      block.  The -c option will print out the contents of all of  the
	      data blocks selected by the -a and -b options.

       ls [-d] [-l] [-p] filespec
	      Print  a listing of the files in the directory filespec.	The -d
	      flag will list deleted entries in the directory.	 The  -l  flag
	      will  list  files using a more verbose format.  The -p flag will
	      list the files in a format which	is  more  easily  parsable  by
	      scripts,	as  well as making it more clear when there are spaces
	      or other non-printing characters at the end of filenames.

       list_deleted_inodes [limit]
	      List deleted inodes, optionally limited to those deleted	within
	      limit seconds ago.  Also available as lsdel.

	      This  command  was  useful  for  recovering from accidental file
	      deletions for ext2 file systems.	Unfortunately, it is not  use-
	      ful  for	this  purpose  if the files were deleted using ext3 or
	      ext4, since the inode's data  blocks  are	 no  longer  available
	      after the inode is released.

       modify_inode filespec
	      Modify  the  contents  of the inode structure in the inode file-
	      spec.  Also available as mi.

       mkdir filespec
	      Make a directory.

       mknod filespec [p|[[c|b] major minor]]
	      Create a special device file (a named pipe, character  or	 block
	      device).	 If  a	character  or  block device is to be made, the
	      major and minor device numbers must be specified.

       ncheck [-c] inode_num ...
	      Take the requested list of inode numbers, and print a listing of
	      pathnames to those inodes.  The -c flag will enable checking the
	      file type information in the directory entry  to	make  sure  it
	      matches the inode's type.

       open [-weficD] [-b blocksize] [-s superblock] device
	      Open  a filesystem for editing.  The -f flag forces the filesys-
	      tem to be opened even if there are some unknown or  incompatible
	      filesystem  features which would normally prevent the filesystem
	      from being opened.  The -e flag  causes  the  filesystem	to  be
	      opened  in  exclusive  mode.   The  -b,  -c,  -i, -s, -w, and -D
	      options behave the same as the command-line options to debugfs.

       punch filespec start_blk [end_blk]
	      Delete the  blocks  in  the  inode  ranging  from	 start_blk  to
	      end_blk.	 If end_blk is omitted then this command will function
	      as a truncate command; that is, all of the  blocks  starting  at
	      start_blk through to the end of the file will be deallocated.

       symlink filespec target
	      Make a symbolic link.

       pwd    Print the current working directory.

       quit   Quit debugfs

       rdump directory[...] destination
	      Recursively dump directory, or multiple directories, and all its
	      contents (including regular files,  symbolic  links,  and	 other
	      directories)  into  the  named  destination,  which should be an
	      existing directory on the native filesystem.

       rm pathname
	      Unlink pathname.	If this causes the inode pointed to  by	 path-
	      name  to	have  no  other references, deallocate the file.  This
	      command functions as the unlink() system call.

       rmdir filespec
	      Remove the directory filespec.

       setb block [count]
	      Mark the block number block as allocated.	 If the optional argu-
	      ment  count is present, then count blocks starting at block num-
	      ber block will be marked as allocated.

       set_block_group bgnum field value
	      Modify the block group descriptor specified by bgnum so that the
	      block group descriptor field field has value value.  Also avail-
	      able as set_bg.

       seti filespec [num]
	      Mark inode filespec as in use in the inode bitmap.   If  num  is
	      specified, also set num-1 inodes after the specified inode.

       set_inode_field filespec field value
	      Modify  the  inode specified by filespec so that the inode field
	      field has value value.  The list of valid inode fields which can
	      be  set  via this command can be displayed by using the command:
	      set_inode_field -l Also available as sif.

       set_mmp_value field value
	      Modify the multiple-mount protection (MMP) data so that the  MMP
	      field field has value value.  The list of valid MMP fields which
	      can be set via this command can be displayed by using  the  com-
	      mand: set_mmp_value -l Also available as smmp.

       set_super_value field value
	      Set  the	superblock  field  field  to value.  The list of valid
	      superblock fields which can be set via this command can be  dis-
	      played  by  using the command: set_super_value -l Also available
	      as ssv.

       show_super_stats [-h]
	      List the contents	 of  the  super	 block	and  the  block	 group
	      descriptors.   If	 the  -h  flag	is  given,  only print out the
	      superblock contents. Also available as stats.

       stat filespec
	      Display the contents of the inode structure of the  inode	 file-
	      spec.

       testb block [count]
	      Test  if	the  block  number block is marked as allocated in the
	      block bitmap.  If the optional argument count is	present,  then
	      count blocks starting at block number block will be tested.

       testi filespec
	      Test  if	the inode filespec is marked as allocated in the inode
	      bitmap.

       undel <inode_number> [pathname]
	      Undelete the specified inode number (which must be surrounded by
	      angle brackets) so that it and its blocks are marked in use, and
	      optionally link the recovered inode to the  specified  pathname.
	      The  e2fsck  command  should always be run after using the undel
	      command to recover deleted files.

	      Note that if you are recovering a large number of deleted files,
	      linking the inode to a directory may require the directory to be
	      expanded, which could allocate a block that had been used by one
	      of  the  yet-to-be-undeleted  files.  So it is safer to undelete
	      all of the inodes without specifying a destination pathname, and
	      then  in	a  separate pass, use the debugfs link command to link
	      the inode to the destination pathname, or use  e2fsck  to	 check
	      the  filesystem  and  link  all  of  the recovered inodes to the
	      lost+found directory.

       unlink pathname
	      Remove the link specified by pathname to an  inode.   Note  this
	      does not adjust the inode reference counts.

       write source_file out_file
	      Copy  the	 contents  of source_file into a newly-created file in
	      the filesystem named out_file.

       zap_block [-f filespec] [-o offset] [-l length] [-p pattern] block_num

       Overwrite the block specified by
	      block_num with zero (NUL) bytes, or if -p is given use the  byte
	      specified by pattern.  If -f is given then block_num is relative
	      to the start of the file given  by  filespec.   The  -o  and  -l
	      options  limit the range of bytes to zap to the specified offset
	      and length relative to the start of the block.

       zap_block [-f filespec] [-b bit] block_num
	      Bit-flip portions of the physical block_num.  If	-f  is	given,
	      then block_num is a logical block relative to the start of file-
	      spec.

ENVIRONMENT VARIABLES
       DEBUGFS_PAGER, PAGER
	      The debugfs program always pipes the output of the some commands
	      through	 a    pager    program.	   These   commands   include:
	      show_super_stats (stats), list_directory	(ls),  show_inode_info
	      (stat),  list_deleted_inodes  (lsdel), and htree_dump.  The spe-
	      cific pager can explicitly specified by the DEBUGFS_PAGER	 envi-
	      ronment variable, and if it is not set, by the PAGER environment
	      variable.

	      Note that since a pager is always used, the less(1) pager is not
	      particularly appropriate, since it clears the screen before dis-
	      playing the output of the command	 and  clears  the  output  the
	      screen  when  the pager is exited.  Many users prefer to use the
	      less(1) pager for most purposes, which is why the	 DEBUGFS_PAGER
	      environment  variable  is available to override the more general
	      PAGER environment variable.

AUTHOR
       debugfs was written by Theodore Ts'o <tytso@mit.edu>.

SEE ALSO
       dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8), ext4(5)



E2fsprogs version 1.42.12	  August 2014			    DEBUGFS(8)