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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
              option, 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
              inode and group bitmaps are not read initially.  This can be useful for  file  sys-
              tems 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 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 (in bytes) for the file system, rather  than
              detecting  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 begin-
              ning 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 primarily 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 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.

       -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-de-
              vice.e2undo in the directory specified via the E2FSPROGS_UNDO_DIR environment vari-
              able.

              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 for-
       ward 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 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 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
              logical_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 con-
              sole.  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 attribute 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.
              Additionally, 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 op-
              tion is given set the owner, group and permissions information on out_file to match
              filespec.

       dump_mmp [mmp_block]
              Display  the  multiple-mount protection (mmp) field values.  If mmp_block is speci-
              fied 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  for-
              mat.

       dump_extents [-n] [-l] filespec
              Dump  the  the  extent tree of the inode filespec.  The -n flag will cause dump_ex-
              tents 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  file
              system  data structures.   Hence, the values displayed may not necessarily by accu-
              rate 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
              clearing 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  ex-
              tents  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 al-
              located.

       freefrag [-c chunk_kb]
              Report  free  space fragmentation on the currently open file system.  If the -c op-
              tion 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
              command line.

       inode_dump [-b]|[-e]|[-x] filespec
              Print the contents of the inode data structure in hex and ASCII format.  The -b op-
              tion  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 extra inode space interpreted and extended attributes.  This is useful  to
              debug corrupted inodes containing extended attributes.

       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  su-
              perblock 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  ex-
              ternal 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
              supplied as a comma-separated list in blocks; the blocks themselves should be read-
              able  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
              directory entries (if any) to this inode.  See the rm(1) command if you wish to un-
              link a file.

       lcd directory
              Change the current working directory of the debugfs process to directory on the na-
              tive 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] [-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 -S option causes logdump to print the contents of the journal superblock.

              The  -a  option  causes the logdump program to print the contents of all of the de-
              scriptor 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
              replayed.

       ls [-l] [-c] [-d] [-p] [-r] filespec
              Print a listing of the files in the directory filespec.  The -c flag causes  direc-
              tory  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-print-
              ing 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 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] [-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
              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 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  allo-
              cated.

       set_block_group bgnum field value
              Modify  the  block  group descriptor specified by bgnum so that the block group de-
              scriptor 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
              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_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
              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  destina-
              tion pathname, 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
              inode 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
              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  ap-
              propriate,  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 1.46.5                  December 2021                                DEBUGFS(8)

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