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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | SPECIFYING FILES | COMMANDS | ENVIRONMENT VARIABLES | AUTHOR | SEE ALSO | COLOPHON |
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DEBUGFS(8) System Manager's Manual DEBUGFS(8)
debugfs - ext2/ext3/ext4 file system debugger
debugfs [ -DVwcin ] [ -b blocksize ] [ -s superblock ] [ -f
cmd_file ] [ -R request ] [ -d data_source_device ] [ -z
undo_file ] [ 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 system.
device is a block device (e.g., /dev/sdXX) or a file containing
the file system.
-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 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 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 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.
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 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
command cd.
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 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 [-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 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 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 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 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 [-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 extended 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 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.
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 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 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 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 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 <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 filespec.
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.
debugfs was written by Theodore Ts'o <[email protected]>.
dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8), ext4(5)
This page is part of the e2fsprogs (utilities for ext2/3/4
filesystems) project. Information about the project can be found
at ⟨http://e2fsprogs.sourceforge.net/⟩. It is not known how to
report bugs for this man page; if you know, please send a mail to
[email protected]. This page was obtained from the project's
upstream Git repository
⟨git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git⟩ on
2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-05-20.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to [email protected]
E2fsprogs version 1.47.1 May 2024 DEBUGFS(8)
Pages that refer to this page: ext4(5), e2freefrag(8), e2fsck(8), e2image(8), tune2fs(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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