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 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 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  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 filesystem).  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 dam-
	      aged/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 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 [-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  num-
	      ber 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.

       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 func-
	      tions, 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 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 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 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 permissions of the new inode.  (If the directory bit is set on the mode, the alloca-
	      tion 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.

       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 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 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] [output_file]
	      Dump  the  contents  of  the ext3 journal.  By default, dump the journal inode as specified in the superblock.  However, this can be
	      overridden with the -i option, which dumps the journal from the internal inode given by filespec.  A regular file containing journal
	      data  can  be specified using the -f option.  Finally, the -s option utilizes the backup information in the superblock to locate the
	      journal.

	      The -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 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 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 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 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 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, -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  trun-
	      cate 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 direc-
	      tories) 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 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 descriptor 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 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 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 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  con-
	      tents. Also available as stats.

       stat filespec
	      Display the contents of the inode structure of the inode filespec.

       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 com-
	      mand 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 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  explic-
	      itly 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 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 envi-
	      ronment 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)