ext2/ext3/ext4 file system debugger
see also :
dumpe2fs - tune2fs - e2fsck - mke2fs
[ -DVwci ] [ -b blocksize ] [
-s superblock ] [ -f cmd_file ] [
-R request ] [ -d
data_source_device ] [ device ]
add an example, a script, a trick and tips
no example yet ...
... Feel free to add your own example above to help other Linux-lovers !
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 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
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 filesystem). 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 will
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
print the version number of debugfs and exit.
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.
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
specified, write out any changes to the superblock and block
group descriptors to all of the backup superblocks, not just to
the master superblock.
Clear the contents of the inode file.
dirsearch filespec filename
Search the directory filespec for filename.
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
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 cause
dump_extents to only display the leaf nodes in the extent
(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 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.
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.)
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
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.
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 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.
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 link to
filespec. Note this does not adjust the inode reference
logdump [-acs] [-b<block>] [-i<filespec>]
Dump the contents of the ext3 journal. By default, the journal
inode as specified in the superblock. However, this can be
overridden with the -i option, which uses an inode
specifier to specify the journal to be used. A 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 [-l] [-d] [-p] filespec
Print a listing of the files in the directory filespec.
The -l flag will list files using a more verbose format.
The -d flag will list deleted entries in the directory.
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
Modify the contents of the inode structure in the inode
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 [-w] [-e] [-f] [-i] [-c] [-D] [-b blocksize] [-s
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
Print the current working directory.
rdump directory destination
Recursively dump directory 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
pathname 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
argument count is present, then count blocks
starting at block number block will be marked as
set_block_group bgnum field value
Modify the block group descriptor specified by bgnum so
that the block group descriptor field field has value
seti filespec [num]
Mark inode filespec as in use in the inode bitmap. If
num is specified, also set num-1 inodes after the
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
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
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
List the contents of the super block and the block group
descriptors. If the -h flag is given, only print out the
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 tested.
Test if the inode filespec is marked as allocated in the
undel <inode num> [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
Create a file in the filesystem named out_file, and copy
the contents of source_file into the destination file.
The debugfs program always pipes the output of the some
commands through a pager program. These commands include:
show_inode_info, list_deleted_inodes, 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.
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.
tune2fs , e2fsck , mke2fs
was written by Theodore Ts’o