NAME debugfs - ext2/ext3/ext4 file system debugger

SYNOPSIS debugfs [ -Vwci ] [ -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 ini- tially. 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 alloca- tion 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 filesys- tem). 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.

-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 com- mand cd.

COMMANDS This is a list of the commands which debugfs supports.

bmap filespec logical_block Print the physical block number corresponding to the logical block number logical_block in the inode 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 spec- ified, write out any changes to the superblock and block group descriptors to all of the backup superblocks, not just to the master superblock.

clri file Clear the contents of the inode file.

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_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 cause dump_extents to only dis- play 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.

find_free_block [count [goal]] Find the first count free blocks, starting from goal and allo- cate it.

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 per- missions of the new inode. (If the directory bit is set on the mode, the allocation routine will function differently.)

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.

freei filespec Free the inode specified by filespec.

help Print a list of commands understood by debugfs(8).

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 ta- ble) 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 struc- tures; 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 link to filespec. Note this does not adjust the inode reference counts.

logdump [-acs] [-b<block>] [-i<filespec>] [-f<journal_file>] [out- put_file] Dump the contents of the ext3 journal. By default, the journal inode as specified in the superblock. However, this can be overridden with the -i option, which uses an inode specifier to specify the journal to be used. A 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 [-l] [-d] [-p] filespec Print a listing of the files in the directory filespec. The -l flag will list files using a more verbose format. The -d flag will list deleted entries in the directory. 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.

modify_inode filespec Modify the contents of the inode structure in the inode file- spec.

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 inode_num ... Take the requested list of inode numbers, and print a listing of pathnames to those inodes.

open [-w] [-e] [-f] [-i] [-c] [-b blocksize] [-s superblock] device Open a filesystem for editing. The -f flag forces the filesys- tem 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, and -w options behave the same as the command-line options to debugfs.

pwd Print the current working directory.

quit Quit debugfs

rdump directory destination Recursively dump directory and all its contents (including regu- lar 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 path- name 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 argu- ment count is present, then count blocks starting at block num- ber 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.

seti filespec Mark inode filespec as in use in the inode bitmap.

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

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

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.

stat filespec Display the contents of the inode structure of the inode file- spec.

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 num> [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 Create a file in the filesystem named out_file, and copy the contents of source_file into the destination file.

ENVIRONMENT VARIABLES DEBUGFS_PAGER, PAGER The debugfs(8) program always pipes the output of the some com- mands through a pager program. These commands include: show_super_stats, list_directory, show_inode_info, list_deleted_inodes, 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 dis- playing 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 Tso <>.

SEE ALSO dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8)

E2fsprogs version 1.41.12 May 2010 DEBUGFS(8)