debugfs (8)

Leading comments

Copyright 1993, 1994, 1995 by Theodore Ts'o.  All Rights Reserved.
This file may be copied under the terms of the GNU Public License.

(The comments found at the beginning of the groff file "man8/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 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>.

SEE ALSO

dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8), ext4(5)