debugfs - ext2/ext3/ext4 file system debugger
] [ -b
blocksize ] [ -s
] [ -f
cmd_file ] [ -R
request ] [ -d
] [ device ]
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.
is the special file corresponding to the device containing the
file system (e.g /dev/hdXX).
- Specifies that the file system should be opened in read-write mode.
Without this option, the file system is opened in read-only mode.
- 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.
- 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
- -f cmd_file
- Causes debugfs to read in commands from cmd_file, and
execute them. When debugfs is finished executing those commands, it
- 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
- print the version number of debugfs and exit.
commands take a filespec
as an argument to specify an
inode (as opposed to a pathname) in the filesystem which is currently opened
. The filespec
argument may be specified in two forms.
The first form is an inode number surrounded by angle brackets, e.g.,
. 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
. This may be modified by using the debugfs
This is a list of the commands which debugfs
- blocks filespace
- Print the blocks used by the inode filespec to stdout.
- bmap filespec logical_block
- Print the physical block number corresponding to the logical block number
logical_block in the inode filespec.
- 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
- clri filespec
- Clear the contents of the inode filespec.
- dirsearch filespec filename
- Search the directory filespec for filename.
- Mark the filesystem as dirty, so that the superblocks will be written on
- 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.
- Display the multiple-mount protection (mmp) field values.
- dx_hash [-h hash_alg] [-s hash_seed] filename
- Calculate the directory hash of filename. The hash algorithm
specified with -h may be legacy, half_md4, or
tea. The hash seed specified with -s must be in UUID
- 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.)
- expand_dir filespec
- Expand the directory filespec.
- feature [fs_feature] [-fs_feature] ...
- Set or clear various filesystem features in the superblock. After setting
or clearing any filesystem features that were requested, print the current
state of the filesystem feature set.
- filefrag [-dvr] filespec
- Print the number of contiguous extents in filespec. If
filespec is a directory and the -d option is not specified,
filefrag will print the number of contiguous extents for each file
in the directory. The -v option will cause 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
- 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
- freei filespec [num]
- Free the inode specified by filespec. If num is specified,
also clear num-1 inodes after the specified inode.
- Print a list of commands understood by debugfs.
- htree_dump filespec
- Dump the hash-indexed directory filespec, showing its tree
- 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
- imap filespec
- Print the location of the inode data structure (in the inode table) of the
- 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
- 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
- logdump [-acs] [-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 -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 [-d] [-l] [-p] filespec
- Print a listing of the files in the directory filespec. 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.
- 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
- open [-weficD] [-b blocksize] [-s superblock] device
- Open a filesystem for editing. The -f flag forces the filesystem to
be opened even if there are some unknown or incompatible filesystem
features which would normally prevent the filesystem from being opened.
The -e flag causes the filesystem to be opened in exclusive mode.
The -b, -c, -i, -s, -w, and -D
options behave the same as the command-line options to
- 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.
- Print the current working directory.
- 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
- 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
- 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
- testi filespec
- Test if the inode filespec is marked as allocated in the inode
- 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
- 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]
- 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
- 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
was written by Theodore Ts'o <email@example.com>.