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 resize2fs-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 [-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.

       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 conents 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  Mark the filesystem as dirty, so that the superblocks will be
              written on exit.

       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.)

       ea_get [-f outfile] 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] 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.

       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 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] [-j 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.

       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 [-acsO] [-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 -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.

              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] [-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, -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.

       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_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.

       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 2017-03-13.
       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 1.43.5-WIP    February 2017                     DEBUGFS(8)