man > DEBUGFS(8)

DEBUGFS(8)                             System Manager's Manual                            DEBUGFS(8)

NAME
       debugfs - ext2/ext3/ext4 file system debugger

SYNOPSIS
       debugfs  [  -DVwcin  ] [ -b blocksize ] [ -s superblock ] [ -f cmd_file ] [ -R request ] [ -d
       data_source_device ] [ -z undo_file ] [ 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 a block device (e.g., /dev/sdXX) or a file containing the file system.

OPTIONS
       -w     Specifies  that the file system should be opened in read-write mode.  Without this op‐
              tion, the file system is opened in read-only mode.

       -n     Disables metadata checksum verification.  This should only be used if you believe  the
              metadata to be correct despite the complaints of e2fsprogs.

       -c     Specifies that the file system should be opened in catastrophic mode, in which the in‐
              ode  and  group  bitmaps  are not read initially.  This can be useful for file systems
              with significant corruption, but because of this, catastrophic mode  forces  the  file
              system 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 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 (in bytes) for the file system, rather than de‐
              tecting the correct block size automatically.  (This option is rarely  needed;  it  is
              used primarily when the file system is extremely badly damaged/corrupted.)

       -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 file system).  If you specify the -s option, you must also provide  the  blocksize
              of the file system via the -b option.   (This option is rarely needed; it is used pri‐
              marily when the file system is extremely badly damaged/corrupted.)

       -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 Di‐
              rect I/O.

       -R request
              Causes debugfs to execute the single command request, and then exit.

       -V     print the version number of debugfs and exit.

       -z undo_file
              Before overwriting a file system block, write the old contents of the block to an undo
              file.  This undo file can be used with e2undo(8) to restore the old  contents  of  the
              file system should something go wrong.  If the empty string is passed as the undo_file
              argument,  the  undo file will be written to a file named debugfs-device.e2undo in the
              directory specified via the E2FSPROGS_UNDO_DIR environment variable.

              WARNING: The undo file cannot be used to recover from a power or system crash.

SPECIFYING FILES
       Many debugfs commands take a filespec as an argument to specify an inode  (as  opposed  to  a
       pathname) in the file system 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 file system which is currently
       opened by debugfs.  If not, the pathname is interpreted relative to the current  working  di‐
       rectory 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 filespec
              Print the blocks used by the inode filespec to stdout.

       bmap [ -a ] filespec logical_block [physical_block]
              Print or set the physical block number corresponding to the logical block number logi‐
              cal_block in the inode filespec.  If the -a flag is specified, try to allocate a block
              if necessary.

       block_dump '[ -x ] [-f filespec] block_num
              Dump  the file system 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.   If the -x option is specified, the block is interpreted as an extended at‐
              tribute block and printed to show the structure of extended attribute data structures.

       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 su‐
              perblocks, not just to the master superblock.

       clri filespec
              Clear the contents of the inode filespec.

       copy_inode source_inode destination_inode
              Copy the contents of the inode structure in source_inode and use it to  overwrite  the
              inode structure at destination_inode.

       dirsearch filespec filename
              Search the directory filespec for filename.

       dirty [-clean]
              Mark the file system as dirty, so that the superblocks will be written on exit.  Addi‐
              tionally, clear the superblock's valid flag, or set it if -clean is specified.

       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 file‐
              spec.

       dump_mmp [mmp_block]
              Display the multiple-mount protection (mmp) field values.  If mmp_block  is  specified
              then  verify  and  dump  the MMP values from the given block number, otherwise use the
              s_mmp_block field in the superblock to locate and use the existing MMP block.

       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 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_ex‐
              tents 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 system
              data  structures.    Hence,  the  values displayed may not necessarily by accurate and
              does not indicate a problem or corruption in the file system.)

       dump_unused
              Dump unused blocks which contain non-null bytes.

       ea_get [-f outfile]|[-xVC] [-r] filespec attr_name
              Retrieve the value of the extended attribute attr_name in the file filespec and  write
              it either to stdout or to outfile.

       ea_list filespec
              List the extended attributes associated with the file filespec to standard output.

       ea_set [-f infile] [-r] filespec attr_name attr_value
              Set  the  value of the extended attribute attr_name in the file filespec to the string
              value attr_value or read it from infile.

       ea_rm filespec attr_names...
              Remove the extended attribute attr_name from the file filespec.

       expand_dir filespec
              Expand the directory filespec.

       fallocate filespec start_block [end_block]
              Allocate and map uninitialized blocks into filespec between logical block  start_block
              and  end_block,  inclusive.  If end_block is not supplied, this function maps until it
              runs out of free disk blocks or the maximum file size is reached.   Existing  mappings
              are left alone.

       feature [fs_feature] [-fs_feature] ...
              Set  or clear various file system features in the superblock.  After setting or clear‐
              ing any file system features that were requested, print the current state of the  file
              system 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 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 speci‐
              fies 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  allo‐
              cated.

       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.

       get_quota quota_type id
              Display quota information for given quota type (user, group, or project) and ID.

       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 com‐
              mand line.

       inode_dump [-b]|[-e]|[-x] filespec
              Print the contents of the inode data structure in hex and ASCII format.  The -b option
              causes the command to only dump the contents of the i_blocks  array.   The  -e  option
              causes  the  command to only dump the contents of the extra inode space, which is used
              to store in-line extended attributes. The -x option causes the command to dump the ex‐
              tra inode space interpreted and extended attributes.  This is  useful  to  debug  cor‐
              rupted inodes containing extended attributes.

       imap filespec
              Print the location of the inode data structure (in the inode table) of the inode file‐
              spec.

       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)  pro‐
              gram.   This is just a call to the low-level library, which sets up the superblock and
              block descriptors.

       journal_close
              Close the open journal.

       journal_open [-c] [-v ver] [-f ext_jnl]
              Opens the journal for reading and writing.  Journal checksumming  can  be  enabled  by
              supplying  -c; checksum formats 2 and 3 can be selected with the -v option.  An exter‐
              nal journal can be loaded from ext_jnl.

       journal_run
              Replay all transactions in the open journal.

       journal_write [-b blocks] [-r revoke] [-c] file
              Write a transaction to the open journal.  The list of blocks to write should  be  sup‐
              plied  as  a  comma-separated list in blocks; the blocks themselves should be readable
              from file.  A list of blocks to revoke can be supplied as a  comma-separated  list  in
              revoke.   By  default,  a commit record is written at the end; the -c switch writes an
              uncommitted transaction.

       kill_file filespec
              Deallocate the inode filespec and its blocks.  Note that this does not remove any  di‐
              rectory 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
              file system.

       list_quota quota_type
              Display quota information for given quota type (user, group, or project).

       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 [-acsOS] [-b block] [-n num_trans ] [-i filespec] [-f journal_file] [output_file]
              Dump the contents of the ext3 journal.  By default, dump the journal inode  as  speci‐
              fied  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  contain‐
              ing  journal  data  can be specified using the -f option.  Finally, the -s option uti‐
              lizes the backup information in the superblock to locate the journal.

              The -S option causes logdump to print the contents of the journal superblock.

              The -a option causes the logdump to print  the  contents  of  all  of  the  descriptor
              blocks.   The  -b option causes logdump to print all journal records that 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.

              The  -O option causes logdump to display old (checkpointed) journal entries.  This can
              be used to try to track down journal problems even after  the  journal  has  been  re‐
              played.

              The -n option causes logdump to continue past a journal block which is missing a magic
              number.   Instead, it will stop only when the entire log is printed or after num_trans
              transactions.

       ls [-l] [-c] [-d] [-p] [-r] filespec
              Print a listing of the files in the directory filespec.  The -c flag causes  directory
              block  checksums  (if present) to be displayed.  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.  The -r flag will force the printing of the filename, even if it  is
              encrypted.

       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  charac‐
              ter  or  block device is to be made, the major and minor device numbers must be speci‐
              fied.

       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] [-d image_filename] [-s superblock] [-z undo_file] device
              Open a file system for editing.  The -f flag forces the file system to be opened  even
              if  there  are  some unknown or incompatible file system features which would normally
              prevent the file system from being opened.  The -e flag causes the file system  to  be
              opened  in exclusive mode.  The -b, -c, -d, -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 omit‐
              ted 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 file system.

       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 allocated.

       set_block_group bgnum field value
              Modify  the block group descriptor specified by bgnum so that the block group descrip‐
              tor field field has value value.  Also available as set_bg.

       set_current_time time
              Set current time in seconds since Unix epoch to use when setting file system fields.

       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  dis‐
              played 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_debugfs_params
              Display debugfs parameters such as information about currently opened file system.

       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.

       supported_features
              Display file system features supported by this version of debugfs.

       testb block [count]
              Test if the block number block is marked as allocated in the block bitmap.  If the op‐
              tional 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 un‐
              delete all of the inodes without specifying a destination pathname, and then in a sep‐
              arate pass, use the debugfs link command to link the inode to  the  destination  path‐
              name,  or  use e2fsck to check the file system 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  in‐
              ode reference counts.

       write source_file out_file
              Copy  the  contents  of source_file into a newly-created file in the file system 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 log‐
              ical 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 pro‐
              gram.  These commands include: show_super_stats (stats), list_directory (ls), show_in‐
              ode_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  appro‐
              priate,  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 AT mit.edu>.

SEE ALSO
       dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8), ext4(5)

E2fsprogs version 1.47.0                    February 2023                                 DEBUGFS(8)