Provided by: e2fsprogs_1.44.1-1ubuntu1.4_amd64 
NAME
debugfs - ext2/ext3/ext4 file system debugger
SYNOPSIS
debugfs [ -DVwcin ] [ -b blocksize ] [ -s superblock ] [ -f cmd_file ] [ -R request ] [ -d
data_source_device ] [ -z undo_file ] [ device ]
DESCRIPTION
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
-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 debugfs-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
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
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 contents 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 [-clean]
Mark the filesystem as dirty, so that the superblocks will be written on exit. Additionally,
clear the superblock's valid flag, or set it if -clean is specified.
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.)
dump_unused
Dump unused blocks which contain non-null bytes.
ea_get [-f outfile]|[-xVC] [-r] 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] [-r] 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.
get_quota quota_type id
Display quota information for given quota type (user, group, or project) and ID.
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] [-f 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.
list_quota quota_type
Display quota information for given quota type (user, group, or project).
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 [-acsOS] [-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 -S option causes logdump to print the contents of the journal superblock.
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 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] [-d image_filename] [-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, -d,
-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.
set_current_time time
Set current time in seconds since Unix epoch to use when setting filesystem fields.
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_debugfs_params
Display debugfs parameters such as information about currently opened filesystem.
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.
supported_features
Display filesystem features supported by this version of debugfs.
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
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
debugfs was written by Theodore Ts'o <tytso@mit.edu>.
SEE ALSO
dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8), ext4(5)
E2fsprogs version 1.44.1 March 2018 DEBUGFS(8)