DEBUGFS(8) System Manager's Manual DEBUGFS(8)
debugfs - ext2/ext3/ext4 file system debugger
debugfs [ -DVwci ] [ -b blocksize ] [ -s superblock ] [ -f cmd_file ] [
-R request ] [ -d data_source_device ] [ device ]
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
device is the special file corresponding to the device containing the
file system (e.g /dev/hdXX).
-w Specifies that the file system should be opened in read-write
mode. Without this option, the file system is opened in read-
-c Specifies that the file system should be opened in catastrophic
mode, in which the inode and group bitmaps are not read ini-
tially. 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 alloca-
tion 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
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.
Forces the use of the given block size for the file system,
rather than detecting the correct block size as normal.
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 filesys-
tem). If you specify the -s option, you must also provide the
blocksize of the filesystem via the -b option.
Causes debugfs to read in commands from cmd_file, and execute
them. When debugfs is finished executing those commands, it
-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.
Causes debugfs to execute the single command request, and then
-V print the version number of debugfs and exit.
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 com-
This is a list of the commands which debugfs supports.
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.
Dump the contents of the inode filespec to stdout.
Change the current working directory to filespec.
Change the root directory to be the directory filespec.
Close the currently open file system. If the -a option is spec-
ified, write out any changes to the superblock and block group
descriptors to all of the backup superblocks, not just to the
Clear the contents of the inode filespec.
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.
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 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.)
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
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 allo-
cate 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 per-
missions 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 sys-
tem. 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.
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.
Print the contents of the inode data structure in hex and ASCII
Print the location of the inode data structure (in the inode ta-
ble) 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 struc-
tures; to do this, use the mke2fs(8) program. This is just a
call to the low-level library, which sets up the superblock and
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.
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 [-acs] [-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.
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, 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 use-
ful 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 the contents of the inode structure in the inode file-
spec. Also available as mi.
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] device
Open a filesystem for editing. The -f flag forces the filesys-
tem 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.
Unlink pathname. If this causes the inode pointed to by path-
name to have no other references, deallocate the file. This
command functions as the unlink() system call.
Remove the directory filespec.
setb block [count]
Mark the block number block as allocated. If the optional argu-
ment count is present, then count blocks starting at block num-
ber 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 avail-
able 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 com-
mand: 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 dis-
played by using the command: set_super_value -l Also available
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.
Display the contents of the inode structure of the inode file-
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.
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 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
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 file-
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 spe-
cific pager can explicitly specified by the DEBUGFS_PAGER envi-
ronment variable, and if it is not set, by the PAGER environment
Note that since a pager is always used, the less(1) pager is not
particularly appropriate, since it clears the screen before dis-
playing 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.
debugfs was written by Theodore Ts'o <firstname.lastname@example.org>.
dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8), ext4(5)
E2fsprogs version 1.42.13 May 2015 DEBUGFS(8)
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