debugfs man page on Archlinux

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DEBUGFS(8)							    DEBUGFS(8)

       debugfs - ext2/ext3/ext4 file system debugger

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

       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
       device is the special file corresponding to the device  containing  the
       file system (e.g /dev/hdXX).

       -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

       -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

       -V     print the version number of debugfs and exit.

       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.

       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.

	      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

       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

       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
	      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 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

       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‐

       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

       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‐

	      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

	      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.

       debugfs was written by Theodore Ts'o <>.

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

E2fsprogs version 1.42.9	 December 2013			    DEBUGFS(8)

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