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DEBUGFS(8)                                                          DEBUGFS(8)



NAME
       debugfs - ext2/ext3/ext4 file system debugger

SYNOPSIS
       debugfs [ -Vwci ] [ -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 sys-
              tem 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 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 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 commands, it will exit.

       -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.

       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.

       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_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 sys-
              tem.)

       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.

       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.

       freei filespec
              Free the inode specified by filespec.

       help   Print a list of commands understood by debugfs(8).

       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 initial-
              ize  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 refer-
              ence counts.

       logdump [-acs] [-b<block>] [-i<filespec>] [-f<journal_file>] [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 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  -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 ver-
              bose 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 inode_num ...
              Take the requested list of inode numbers, and print a listing of pathnames to those inodes.

       open [-w] [-e] [-f] [-i] [-c] [-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, and -w
              options behave the same as the command-line options to debugfs.

       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,  deallo-
              cate 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
              Mark inode filespec as in use in the inode bitmap.

       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_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 <inode num> [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  destina-
              tion file.

ENVIRONMENT VARIABLES
       DEBUGFS_PAGER, PAGER
              The debugfs(8) program always pipes the output of the some commands through a pager program.  These com-
              mands 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 variable.

              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 <tytsoATmit.edu>.

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



E2fsprogs version 1.41.12          May 2010                         DEBUGFS(8)