DEBUGFS(8)                (August 2021)                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 con-
          taining 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
               systems 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 descrip-
               tor, block and inode allocation bitmaps, and the inode
               table, many debugfs commands will not function prop-
               erly.  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

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               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 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 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 file sys-
          tem 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

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          forward 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 console.  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
               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 struc-
               ture at destination_inode.

          dirsearch filespec filename
               Search the directory filespec for filename.

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          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 speci-
               fied.

          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 val-
               ues.  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 inte-
               rior 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 dis-
               played 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

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               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, inclu-
               sive.  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 speci-
               fied, 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 con-
               tiguous 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 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.

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          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 speci-
               fied, 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 option 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 superblock and block descriptors.

          journal_close
               Close the open journal.

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          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 read-
               able from file.  A list of blocks to revoke can be sup-
               plied 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 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.

     [output_file]
          logdump [-acsOS] [-b block] [-i filespec] [-f journal_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

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               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 (check-
               pointed) 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 pre-
               sent) 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

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               directory entry to make sure it matches the inode's
               type.

     [-z undo_file] device
          open [-weficD] [-b blocksize] [-d image_filename] [-
               s superblock]
               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 nor-
               mally prevent the file system from being opened.  The
               -e flag causes the file system to be opened in exclu-
               sive mode.  The -b, -c, -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 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

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               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 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 spec-
               ified 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 com-
               mand 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

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               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 sur-
               rounded 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 allo-
               cate 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 com-
               mand to link the inode to the destination 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.

     block_num
          zap_block [-f filespec] [-o offset] [-l length] [-p pattern]
               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 spec-
               ified 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

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               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 spec-
               ified 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 environ-
               ment 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)

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