debugfs - ext2/ext3/ext4 file system debugger
debugfs [ -Vwci ] [ -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
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!
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
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
This is a list of the commands which debugfs supports.
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.
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_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 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 file esystem 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
find_free_block [count [goal]]
Find the first count free blocks, starting from goal and
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 not allocated.
Free the inode specified by filespec.
help Print a list of commands understood by debugfs(8).
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 counts.
logdump [-acs] [-b<block>] [-i<filespec>] [-f<journal_file>]
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
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 filenames.
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 inode_num ...
Take the requested list of inode numbers, and print a listing of
pathnames to those inodes.
open [-w] [-e] [-f] [-i] [-c] [-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,
and -w options behave the same as the command-line options to
pwd Print the current working directory.
quit Quit debugfs
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
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 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.
Mark inode filespec as in use in the inode bitmap.
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_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 inode
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(8) program always pipes the output of the some
commands through a pager program. These commands include:
show_super_stats, list_directory, 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.
debugfs was written by Theodore Ts'o <firstname.lastname@example.org>.
dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8)