debugfs - ext2/ext3/ext4 file system debugger
] [ -b
blocksize ] [ -s
] [ -f
cmd_file ] [ -R
request ] [ -d
] [ -z undo_file
] [ device ]
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.
is a block device (e.g., /dev/sdXX) or a file containing the file
- Specifies that the file system should be opened in
read-write mode. Without this option, the file system is opened in
- Disables metadata checksum verification. This should only
be used if you believe the metadata to be correct despite the complaints
- 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
- 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
- -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
- -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.
- 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.
- 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 resize2fs- device.e2undo
in the directory specified via the E2FSPROGS_UNDO_DIR environment
WARNING: The undo file cannot be used to recover from a power or system
commands take a filespec
as an argument to specify an
inode (as opposed to a pathname) in the filesystem which is currently opened
. The filespec
argument may be specified in two forms.
The first form is an inode number surrounded by angle brackets, e.g.,
. 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
. This may be modified by using the debugfs
This is a list of the commands which debugfs
- blocks filespace
- Print the blocks used by the inode filespec to
- bmap [ -a ] filespec logical_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
- 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
- cd filespec
- Change the current working directory to
- chroot filespec
- Change the root directory to be the directory
- 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
- clri filespec
- Clear the contents of the inode filespec.
- copy_inode source_inode
- Copy the conents of the inode structure in
source_inode and use it to overwrite the inode structure at
- dirsearch filespec filename
- Search the directory filespec for
- Mark the filesystem as dirty, so that the superblocks will
be written on exit.
- 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
- 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]
- 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
- 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
- (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.)
- ea_get [-f outfile] 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] filespec attr_name
- Set the value of the extended attribute attr_name in
the file filespec to the string value attr_value or read it
- ea_rm filespec attr_names...
- Remove the extended attribute attr_name from the
- expand_dir filespec
- Expand the directory filespec.
- fallocate filespec start_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
- 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
- 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.
- 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
- 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
- Close the open journal.
- journal_open [-c] [-v ver] [-j 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.
- Replay all transactions in the open journal.
- journal_write [-b blocks] [-r revoke] [-c]
- 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.
- 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
- logdump [-acsO] [-b block] [-i filespec] [-f
- 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
- 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.
- 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
- 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] [-s superblock] [-z
- 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, -w, and
-D options behave the same as the command-line options to
- 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
- symlink filespec target
- Make a symbolic link.
- Print the current working directory.
- 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.
- 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
- 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
- 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
- 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]
- 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
was written by Theodore Ts'o <email@example.com>.