debugfs(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | SPECIFYING FILES | COMMANDS | ENVIRONMENT VARIABLES | AUTHOR | SEE ALSO | COLOPHON

DEBUGFS(8)               System Manager's Manual              DEBUGFS(8)

NAME         top

       debugfs - ext2/ext3/ext4 file system debugger

SYNOPSIS         top

       debugfs [ -DVwcin ] [ -b blocksize ] [ -s superblock ] [ -f
       cmd_file ] [ -R request ] [ -d data_source_device ] [ -z
       undo_file ] [ device ]

DESCRIPTION         top

       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         top

       -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 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         top

       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         top

       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 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.  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 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 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 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
              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 [-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.

       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 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
              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 contents. 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 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 filespec.

ENVIRONMENT VARIABLES         top

       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 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         top

       debugfs was written by Theodore Ts'o <tytso@mit.edu>.

SEE ALSO         top

       dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8), ext4(5)

COLOPHON         top

       This page is part of the e2fsprogs (utilities for ext2/3/4
       filesystems) project.  Information about the project can be found
       at ⟨http://e2fsprogs.sourceforge.net/⟩.  It is not known how to
       report bugs for this man page; if you know, please send a mail to
       man-pages@man7.org.  This page was obtained from the project's
       upstream Git repository
       ⟨git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git⟩ on
       2021-04-01.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-02-28.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

E2fsprogs version 1.46.2      February 2021                   DEBUGFS(8)

Pages that refer to this page: ext4(5)e2freefrag(8)e2fsck(8)e2image(8)tune2fs(8)