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debugfs


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.

       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.

              (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.

       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.
              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
              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

       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
              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 1.42.9 December 2013 DEBUGFS(8)



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