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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 in-
       ode (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.  Af-
	      ter  setting  or	clearing any filesystem	features that were re-
	      quested, 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  di-
	      rectory.	 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 lo-
	      cated.  The second optional argument mode	specifies the  permis-
	      sions  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.

       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  af-
	      ter 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 ma-
	      jor 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 op-
	      tions 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 and all its contents (including regu-
	      lar 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 su-
	      perblock 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  de-
	      scriptors.   If  the  -h	flag  is given,	only print out the su-
	      perblock 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  op-
	      tions  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_su-
	      per_stats	(stats), list_directory	(ls), show_inode_info  (stat),
	      list_deleted_inodes (lsdel), and htree_dump.  The	specific pager
	      can explicitly specified by the DEBUGFS_PAGER environment	 vari-
	      able, 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 1.42.9	 December 2013			    DEBUGFS(8)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | SPECIFYING FILES | COMMANDS | ENVIRONMENT VARIABLES | AUTHOR | SEE ALSO

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