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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 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.

       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  logi‐
              cal_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 con‐
              sole.  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 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 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  for‐
              mat.

       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 filesys‐
              tem  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 allocate it.  Also  avail‐
              able 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  permissions  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  system.   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 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 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 spec‐
              ified 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 con‐
              taining 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 useful  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 filespec.   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 char‐
              acter 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  direc‐
              tory 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 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.

       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 (includ‐
              ing regular files, symbolic links, and other directories) into the  named  destina‐
              tion, which should be an existing 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.  Also available 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 command: 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 displayed 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 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  [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
              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 pat‐
              tern.  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 filespec.

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 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 .

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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