DEBUGFS(8) System Manager's Manual DEBUGFS(8)
NAME
debugfs - ext2/ext3/ext4 file system debugger
SYNOPSIS
debugfs [ -DVwci ] [ -b blocksize ] [ -s superblock ] [ -f cmd_file ] [ -R request ] [ -d data_source_device ]
[ 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 the special file corresponding to the device containing the file system (e.g /dev/hdXX).
OPTIONS
-w Specifies that the file system should be opened in read-write mode. Without this option, the file sys‐
tem is opened in read-only mode.
-c Specifies that the file system should be opened in catastrophic mode, in which the inode and group bit‐
maps 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 for the file system, rather than detecting the correct block
size as normal.
-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.
-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.
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
filespec.
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.
dirsearch filespec filename
Search the directory filespec for filename.
dirty 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 filespec.
dump_mmp
Display the multiple-mount protection (mmp) field values.
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.)
expand_dir filespec
Expand the directory filespec.
feature [fs_feature] [-fs_feature] ...
Set or clear various filesystem features in the superblock. After setting or clearing any filesystem
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.
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.
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 ini‐
tialize 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.
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 counts.
logdump [-acs] [-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 jour‐
nal.
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
This command was useful for recovering from accidental file deletions for ext2 file systems. Unfortu‐
nately, 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] 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, -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 com‐
mand 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 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, deallo‐
cate 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
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_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.
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 destina‐
tion pathname, and then in a separate pass, use the debugfs link command to link the inode to the des‐
tination 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 rela‐
tive to the start of filespec.
ENVIRONMENT VARIABLES
DEBUGFS_PAGER, PAGER
debugfs was written by Theodore Ts'o <[email protected]>.
SEE ALSO
dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8), ext4(5)
E2fsprogs version 1.42.9 December 2013 DEBUGFS(8)
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