Ubuntu Manpage: debugfs - ext2/ext3/ext4 file system debugger

Provided by: e2fsprogs_1.42.13-1ubuntu1.2_amd64

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 system is opened in read-only mode.

-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 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  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 debugfs.  This may be modified by using the
       debugfs command cd.

COMMANDS

This is a list of the commands which debugfs supports.

blocks filespace
Print the blocks used by the inode filespec to stdout.

bmap filespec logical_block
Print the physical block number corresponding to the logical block number
logical_block in the inode 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 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 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.

inode_dump filespec
Print the contents of the inode data structure in hex and ASCII format.

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.

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 journal.

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.

ls [-d] [-l] [-p] filespec
Print a listing of the files in the directory filespec. 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.

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] 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 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 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 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_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 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] 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 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.

AUTHOR

       debugfs was written by Theodore Ts'o <tytso@mit.edu>.