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DEBUGFS(8)									       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 initially.  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 allocation 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 spec-
	      ifying  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 begin-
	      ning  of	the filesystem).  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 sup-
	      port 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 for-
       ward  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
       command 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  logi-
	      cal_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 specified, 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 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  file
	      esystem data structures.	 Hence, the values displayed may not necessarily by accu-
	      rate 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 allocate 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 permissions 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.

       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 table)  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 structures; 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>] [output_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 filespec.

       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 char-
	      acter 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] [-D] [-b blocksize] [-s superblock] device
	      Open a filesystem for editing.  The -f flag forces the filesystem 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.

       pwd    Print the current working directory.

       quit   Quit debugfs

       rdump directory destination
	      Recursively dump directory and all its contents (including regular files,  symbolic
	      links,  and other directories) into the named destination which should be an exist-
	      ing directory on the native filesystem.

       rm pathname
	      Unlink pathname.	If this causes the inode pointed to by pathname 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  argument	count  is
	      present,	then  count blocks starting at block number block will be marked as allo-
	      cated.

       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 displayed 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 filespec.

       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 destina-
	      tion 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  program  always pipes the output of the some commands 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 displaying 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 1.41.14		  December 2010 			       DEBUGFS(8)
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