DEBUGFS(8)														DEBUGFS(8)



NAME
       debugfs - ext2/ext3/ext4 file system debugger

SYNOPSIS
       debugfs [ -DVwci ] [ -b blocksize ] [ -s superblock ] [ -f cmd_file ] [ -R request ] [ -d data_source_device ] [ device ]

DESCRIPTION
       The  debugfs  program  is  an  interactive file system debugger. It can be used to examine and change the state of an ext2,
       ext3, or ext4 file system.
       device is the special file corresponding to the device containing the file system (e.g /dev/hdXX).

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

       -c     Specifies  that  the file system should be opened in catastrophic mode, in which the inode and group bitmaps are not
	      read initially.  This can be useful for filesystems with significant corruption, but because of  this,  catastrophic
	      mode forces the filesystem to be opened read-only.

       -i     Specifies  that device represents an ext2 image file created by the e2image program.  Since the ext2 image file only
	      contains the superblock, block group descriptor, block and inode allocation  bitmaps,  and  the  inode  table,  many
	      debugfs commands will not function properly.  Warning: no safety checks are in place, and debugfs may fail in inter‐
	      esting 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 for the file system, rather than detecting the correct block size as normal.

       -s superblock
	      Causes the file system superblock to be read from the given block number, instead of using  the  primary	superblock
	      (located	at  an offset of 1024 bytes from the beginning of the filesystem).  If you specify the -s option, you must
	      also provide the blocksize of the filesystem via the -b option.

       -f cmd_file
	      Causes debugfs to read in commands from cmd_file, and execute them.  When debugfs is finished executing  those  com‐
	      mands, 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.

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 filespace
	      Print the blocks used by the inode filespec to stdout.

       bmap filespec logical_block
	      Print the physical block number corresponding to the logical block number logical_block in the inode 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 file
	      Clear the contents of the inode file.

       dirsearch filespec filename
	      Search the directory filespec for filename.

       dump [-p] filespec out_file
	      Dump the contents of the inode filespec to the output file out_file.  If the -p option is given set the owner, group
	      and permissions information on out_file to match filespec.

       dump_mmp
	      Display the multiple-mount protection (mmp) field values.

       dx_hash [-h hash_alg] [-s hash_seed] filename
	      Calculate the directory hash of filename.  The hash algorithm specified with -h may be "legacy" "half_md4" or "tea".
	      The hash seed specified with -s must be in UUID 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 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.)

       expand_dir filespec
	      Expand the directory filespec.

       feature [fs_feature] [-fs_feature] ...
	      Set  or clear various filesystem features in the superblock.  After setting or clearing any filesystem features that
	      were requested, print the current state of the filesystem feature set.

       filefrag [-dvr] filespec
	      Print the number of contiguous extents in filespec.  If filespec is a directory and the -d option is not	specified,
	      filefrag will print the number of contiguous extents for each file in the directory.  The -v option will cause file‐
	      frag 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.

       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.)

       freeb block [count]
	      Mark the block number block as not allocated.  If the optional argument count is present, then count blocks starting
	      at block number block will be marked as not allocated.

       freefrag [-c chunk_kb ]
	      Report free space fragmentation on the currently open file system.  If the -c option is specified then the  filefrag
	      command  will print how many free chunks of size chunk_kb can be found in the file system.  The chunk size must be a
	      power of two and be larger than the file system block size.

       freei filespec [num]
	      Free the inode specified by filespec.  If num is specified, also clear num-1 inodes after the specified inode.

       help   Print a list of commands understood by debugfs.

       htree_dump filespec
	      Dump the hash-indexed directory filespec, showing its tree structure.

       icheck block ...
	      Print a listing of the inodes which use the one or more blocks specified on the command line.

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

       init_filesys device blocksize
	      Create an ext2 file system on device with device size blocksize.	Note that this does not fully  initialize  all	of
	      the  data  structures;  to  do this, use the mke2fs(8) program.  This is just a call to the low-level library, which
	      sets up the superblock and block descriptors.

       kill_file filespec
	      Deallocate the inode filespec and its blocks.  Note that this does not remove any directory entries (if any) to this
	      inode.  See the rm(1) command if you wish to unlink a file.

       lcd directory
	      Change the current working directory of the debugfs process to directory on the native filesystem.

       ln filespec dest_file
	      Create a link named dest_file which is a link to filespec.  Note this does not adjust the inode reference counts.

       logdump [-acs] [-b] [-i] [-f] [output_file]
	      Dump the contents of the ext3 journal.  By default, the journal inode as specified in the superblock.  However, this
	      can be overridden with the -i option, which uses an inode specifier to specify the journal to be used.  A file  con‐
	      taining  journal data can be specified using the -f option.   Finally, the -s option utilizes the backup information
	      in the superblock to locate the journal.

	      The -a option causes the logdump program to print the contents of all of	the  descriptor  blocks.   The	-b  option
	      causes logdump to print all journal records that are refer to the specified block.  The -c option will print out the
	      contents of all of the data blocks selected by the -a and -b options.

       ls [-l] [-d] [-p] filespec
	      Print a listing of the files in the directory filespec.  The -l flag will list files using a  more  verbose  format.
	      The  -d  flag will list deleted entries in the directory.  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.

       modify_inode filespec
	      Modify the contents of the inode structure in the inode filespec.

       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 [-w] [-e] [-f] [-i] [-c] [-D] [-b blocksize] [-s superblock] device
	      Open  a  filesystem  for	editing.  The -f flag forces the filesystem to be opened even if there are some unknown or
	      incompatible filesystem features which would normally prevent the filesystem from being opened.  The -e flag  causes
	      the  filesystem  to be opened in exclusive mode.	The -b, -c, -i, -s, -w, and -D options behave the same as the com‐
	      mand-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.

       pwd    Print the current working directory.

       quit   Quit debugfs

       rdump directory destination
	      Recursively dump directory 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 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.

       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

       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

       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

       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.

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

       testb block [count]
	      Test if the block number block is marked as allocated in the block  bitmap.   If	the  optional  argument  count	is
	      present, then count blocks starting at block number block will be tested.

       testi filespec
	      Test if the inode filespec is marked as allocated in the inode bitmap.

       undel  [pathname]
	      Undelete	the  specified	inode  number  (which  must be surrounded by angle brackets) so that it and its blocks are
	      marked in use, and optionally link the recovered inode to the specified pathname.  The e2fsck command should  always
	      be run after using the undel command to recover deleted files.

	      Note  that  if  you are recovering a large number of deleted files, linking the inode to a directory may require the
	      directory to be expanded, which could allocate a block that had been used by one of the  yet-to-be-undeleted  files.
	      So it is safer to undelete all of the inodes without specifying a destination pathname, and then in a separate pass,
	      use the debugfs link command to link the inode to the 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
	      Create a file in the filesystem named out_file, and copy the contents of source_file into the destination file.

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, list_directory, show_inode_info, list_deleted_inodes, 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 vari‐
	      able.

	      Note that since a pager is always used, the less(1) pager is not	particularly  appropriate,  since  it  clears  the
	      screen  before displaying the output of the command and clears the output the screen when the pager is exited.  Many
	      users prefer to use the less(1) pager for most purposes, which is why  the  DEBUGFS_PAGER  environment  variable	is
	      available to override the more general PAGER environment variable.

AUTHOR
       debugfs was written by Theodore Ts'o .

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



E2fsprogs version 1.42.5				     July 2012							DEBUGFS(8)