debugfs

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  com-
              plaints of e2fsprogs.

       -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 (in bytes) for the file
              system, rather than detecting the correct block  size  automati-
              cally.  (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  filesys-
              tem).   If  you specify the -s option, you must also provide the
              blocksize of the filesystem 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 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.

       -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 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 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 log-
              ical block number logical_block in the inode filespec.   If  the
              -a flag is specified, try to allocate a block if necessary.

       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.

       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  filesystem  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 option 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 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 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.)

       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 log-
              ical  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 map-
              pings are left alone.

       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.

       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 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.

       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 external 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 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 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.

       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] [out-
       put_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 -S option causes logdump to print the contents of the  jour-
              nal superblock.

              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 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) jour-
              nal 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 directory block checksums (if present)  to  be  dis-
              played.  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 file-
              names.  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 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] [-d image_filename] [-s  superblock]  [-z
       undo_file] 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, -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 (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.

       set_current_time time
              Set current time in seconds since Unix epoch to use when setting
              filesystem 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 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_debugfs_params
              Display  debugfs  parameters such as information about currently
              opened filesystem.

       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.

       supported_features
              Display   filesystem  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 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 1.44.1          March 2018                        DEBUGFS(8)
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