debugfs

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 1.42.13          May 2015                         DEBUGFS(8)
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