Manual: debugfs
DEBUGFS(8) System Manager's Manual DEBUGFS(8)
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 file systems with significant
corruption, but because of this, catastrophic mode forces the file system 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. de‐
bugfs 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 file system).
If you specify the -s option, you must also provide the blocksize of the file system via the
-b option. (This option is rarely needed; it is used primarily when the file system is ex‐
tremely 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 file system 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 rel‐
ative to the root of the file system 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 '[ -x ] [-f filespec] block_num
Dump the file system 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. If
the -x option is specified, the block is interpreted as an extended attribute block and
printed to show the structure of extended attribute data structures.
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 file system 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 ver‐
ify 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 [-cv] [-h hash_alg] [-s hash_seed] filename
Calculate the directory hash of filename. The -c option will casefold the filename before
calculating the hash. The -v option will make the dx_hash command more verbose and print the
hash algorithm and hash seed to calculate the hash. If a file system is open, use the
hash_seed and default hash_algorithm used by the file system, although these can be overridden
by the -h and -s options. 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 extent tree of the inode filespec. The -n flag will cause dump_extents to only dis‐
play the interior nodes in the extent tree. The -l flag will cause dump_extents to only dis‐
play 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 system 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 ei‐
ther 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 file system features in the superblock. After setting or clearing any
file system features that were requested, print the current state of the file system feature
set.
filefrag [-dvr] filespec
Print the number of contiguous extents in filespec. If filespec is a directory and the -d op‐
tion 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 di‐
rectory.
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 direc‐
tory 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 system. If the -c option is speci‐
fied 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 [-b]|[-e]|[-x] filespec
Print the contents of the inode data structure in hex and ASCII format. The -b option causes
the command to only dump the contents of the i_blocks array. The -e option causes the command
to only dump the contents of the extra inode space, which is used to store in-line extended
attributes. The -x option causes the command to dump the extra inode space interpreted and ex‐
tended attributes. This is useful to debug corrupted inodes containing extended attributes.
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 file
system.
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] [-n num_trans ] [-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 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 op‐
tions.
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.
The -n option causes logdump to continue past a journal block which is missing a magic number.
Instead, it will stop only when the entire log is printed or after num_trans transactions.
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 direc‐
tory. 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 file system for editing. The -f flag forces the file system to be opened even if there
are some unknown or incompatible file system features which would normally prevent the file
system from being opened. The -e flag causes the file system 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 de‐
bugfs.
orphan_inodes
List the orphan inodes in the file system.
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 file system.
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 file system 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 file system.
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 file system 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 [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 direc‐
tory 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 file system 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 refer‐
ence counts.
write source_file out_file
Copy the contents of source_file into a newly-created file in the file system 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 vari‐
able.
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 pur‐
poses, 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 .
SEE ALSO
dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8), ext4(5)
E2fsprogs version 1.47.2 January 2025 DEBUGFS(8)