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 com-
plaints of e2fsprogs.
-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 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. 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 automati-
cally. (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 sys-
tem). 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
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 in-
ode (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 relative 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 com-
mand 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 log-
ical 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 spec-
ified, 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 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 extent tree of the inode filespec. The -n flag will
cause dump_extents to only display the interior nodes in the ex-
tent 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 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 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 log-
ical 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 map-
pings 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 re-
quested, 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 option is not specified, filefrag will
print the number of contiguous extents for each file in the di-
rectory. 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 lo-
cated. The second optional argument mode specifies the permis-
sions 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.
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 con-
tents 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 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
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 jour-
nal_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 jour-
nal 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 se-
lected by the -a and -b options.
The -O option causes logdump to display old (checkpointed) jour-
nal 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 dis-
played. 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 file-
names. 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 use-
ful for this purpose if the files were deleted using ext3 or
ext4, since the inode's data blocks are no longer available af-
ter the inode is released.
modify_inode filespec
Modify the contents of the inode structure in the inode file-
spec. 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 ma-
jor 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 incompati-
ble 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 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 di-
rectories) into the named destination, which should be an exist-
ing directory on the native file system.
rm pathname
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.
rmdir filespec
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.
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 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 su-
perblock fields which can be set via this command can be dis-
played 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 de-
scriptors. If the -h flag is given, only print out the su-
perblock contents. Also available as stats.
stat filespec
Display the contents of the inode structure of the inode file-
spec.
supported_features
Display file system features supported by this version of de-
bugfs.
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 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 reference 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 file-
spec.
ENVIRONMENT VARIABLES
DEBUGFS_PAGER, PAGER
The debugfs program always pipes the output of the some commands
through a pager program. These commands include: show_su-
per_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 vari-
able, 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 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.
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 1.47.0 February 2023 DEBUGFS(8)
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