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DEBUGFS(8)							    DEBUGFS(8)

NAME
       debugfs - ext2/ext3/ext4 file system debugger

SYNOPSIS
       debugfs	[ -Vwci ] [ -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.

       -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.

       bmap filespec logical_block
	      Print the physical block number  corresponding  to  the  logical
	      block number logical_block in the inode 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 file
	      Clear the contents of the inode file.

       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_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 cause dump_extents to  only  dis‐
	      play 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 file esystem 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.

       find_free_block [count [goal]]
	      Find the first count free blocks, starting from goal  and	 allo‐
	      cate it.

       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.)

       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.

       freei filespec
	      Free the inode specified by filespec.

       help   Print a list of commands understood by debugfs(8).

       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 link to filespec.  Note
	      this does not adjust the inode reference counts.

       logdump	[-acs]	[-b<block>]  [-i<filespec>]  [-f<journal_file>]	 [out‐
       put_file]
	      Dump the contents of the ext3 journal.  By default, the  journal
	      inode  as	 specified  in	the  superblock.  However, this can be
	      overridden with the -i option, which uses an inode specifier  to
	      specify  the journal to be used.	A 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 [-l] [-d] [-p] filespec
	      Print a listing of the files in the directory filespec.  The  -l
	      flag  will  list files using a more verbose format.  The -d flag
	      will list deleted entries in the directory.  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.

       modify_inode filespec
	      Modify  the  contents  of the inode structure in the inode file‐
	      spec.

       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 inode_num ...
	      Take the requested list of inode numbers, and print a listing of
	      pathnames to those inodes.

       open [-w] [-e] [-f] [-i] [-c] [-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, and -w options
	      behave the same as the command-line options to debugfs.

       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.

       seti filespec
	      Mark inode filespec as in use in the inode bitmap.

       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

       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

       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.

       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 num> [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
	      Create a file in the filesystem named  out_file,	and  copy  the
	      contents of source_file into the destination file.

ENVIRONMENT VARIABLES
       DEBUGFS_PAGER, PAGER
	      The  debugfs(8) program always pipes the output of the some com‐
	      mands  through  a	 pager	program.   These   commands   include:
	      show_super_stats,	       list_directory,	      show_inode_info,
	      list_deleted_inodes, and htree_dump.   The  specific  pager  can
	      explicitly  specified by the DEBUGFS_PAGER environment 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)

E2fsprogs version 1.41.12	   May 2010			    DEBUGFS(8)
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