1DEBUGFS(8) System Manager's Manual DEBUGFS(8)
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6 debugfs - ext2/ext3/ext4 file system debugger
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9 debugfs [ -DVwci ] [ -b blocksize ] [ -s superblock ] [ -f cmd_file ] [
10 -R request ] [ -d data_source_device ] [ device ]
11
13 The debugfs program is an interactive file system debugger. It can be
14 used to examine and change the state of an ext2, ext3, or ext4 file
15 system.
16 device is the special file corresponding to the device containing the
17 file system (e.g /dev/hdXX).
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20 -w Specifies that the file system should be opened in read-write
21 mode. Without this option, the file system is opened in read-
22 only mode.
23 -c Specifies that the file system should be opened in catastrophic
25 mode, in which the inode and group bitmaps are not read ini‐
26 tially. This can be useful for filesystems with significant
27 corruption, but because of this, catastrophic mode forces the
28 filesystem to be opened read-only.
29 -i Specifies that device represents an ext2 image file created by
31 the e2image program. Since the ext2 image file only contains
32 the superblock, block group descriptor, block and inode alloca‐
33 tion bitmaps, and the inode table, many debugfs commands will
34 not function properly. Warning: no safety checks are in place,
35 and debugfs may fail in interesting ways if commands such as ls,
36 dump, etc. are tried without specifying the data_source_device
37 using the -d option. debugfs is a debugging tool. It has rough
38 edges!
39 -d data_source_device
41 Used with the -i option, specifies that data_source_device
42 should be used when reading blocks not found in the ext2 image
43 file. This includes data, directory, and indirect blocks.
44 -b blocksize
46 Forces the use of the given block size for the file system,
47 rather than detecting the correct block size as normal.
48 -s superblock
50 Causes the file system superblock to be read from the given
51 block number, instead of using the primary superblock (located
52 at an offset of 1024 bytes from the beginning of the filesys‐
53 tem). If you specify the -s option, you must also provide the
54 blocksize of the filesystem via the -b option.
55 -f cmd_file
57 Causes debugfs to read in commands from cmd_file, and execute
58 them. When debugfs is finished executing those commands, it
59 will exit.
60 -D Causes debugfs to open the device using Direct I/O, bypassing
62 the buffer cache. Note that some Linux devices, notably device
63 mapper as of this writing, do not support Direct I/O.
64 -R request
66 Causes debugfs to execute the single command request, and then
67 exit.
68 -V print the version number of debugfs and exit.
70
72 Many debugfs commands take a filespec as an argument to specify an
73 inode (as opposed to a pathname) in the filesystem which is currently
74 opened by debugfs. The filespec argument may be specified in two
75 forms. The first form is an inode number surrounded by angle brackets,
76 e.g., <2>. The second form is a pathname; if the pathname is prefixed
77 by a forward slash ('/'), then it is interpreted relative to the root
78 of the filesystem which is currently opened by debugfs. If not, the
79 pathname is interpreted relative to the current working directory as
80 maintained by debugfs. This may be modified by using the debugfs com‐
81 mand cd.
82
84 This is a list of the commands which debugfs supports.
85 blocks filespace
87 Print the blocks used by the inode filespec to stdout.
88 bmap filespec logical_block
90 Print the physical block number corresponding to the logical
91 block number logical_block in the inode filespec.
92 block_dump [-f filespec] block_num
94 Dump the filesystem block given by block_num in hex and ASCII
95 format to the console. If the -f option is specified, the block
96 number is relative to the start of the given filespec.
97 cat filespec
99 Dump the contents of the inode filespec to stdout.
100 cd filespec
102 Change the current working directory to filespec.
103 chroot filespec
105 Change the root directory to be the directory filespec.
106 close [-a]
108 Close the currently open file system. If the -a option is spec‐
109 ified, write out any changes to the superblock and block group
110 descriptors to all of the backup superblocks, not just to the
111 master superblock.
112 clri filespec
114 Clear the contents of the inode filespec.
115 dirsearch filespec filename
117 Search the directory filespec for filename.
118 dirty Mark the filesystem as dirty, so that the superblocks will be
120 written on exit.
121 dump [-p] filespec out_file
123 Dump the contents of the inode filespec to the output file
124 out_file. If the -p option is given set the owner, group and
125 permissions information on out_file to match filespec.
126 dump_mmp
128 Display the multiple-mount protection (mmp) field values.
129 dx_hash [-h hash_alg] [-s hash_seed] filename
131 Calculate the directory hash of filename. The hash algorithm
132 specified with -h may be legacy, half_md4, or tea. The hash
133 seed specified with -s must be in UUID format.
134 dump_extents [-n] [-l] filespec
136 Dump the the extent tree of the inode filespec. The -n flag
137 will cause dump_extents to only display the interior nodes in
138 the extent tree. The -l flag will cause dump_extents to only
139 display the leaf nodes in the extent tree.
140 (Please note that the length and range of blocks for the last
142 extent in an interior node is an estimate by the extents library
143 functions, and is not stored in filesystem data structures.
144 Hence, the values displayed may not necessarily by accurate and
145 does not indicate a problem or corruption in the file system.)
146 expand_dir filespec
148 Expand the directory filespec.
149 feature [fs_feature] [-fs_feature] ...
151 Set or clear various filesystem features in the superblock.
152 After setting or clearing any filesystem features that were
153 requested, print the current state of the filesystem feature
154 set.
155 filefrag [-dvr] filespec
157 Print the number of contiguous extents in filespec. If filespec
158 is a directory and the -d option is not specified, filefrag will
159 print the number of contiguous extents for each file in the
160 directory. The -v option will cause filefrag print a tabular
161 listing of the contiguous extents in the file. The -r option
162 will cause filefrag to do a recursive listing of the directory.
163 find_free_block [count [goal]]
165 Find the first count free blocks, starting from goal and allo‐
166 cate it. Also available as ffb.
167 find_free_inode [dir [mode]]
169 Find a free inode and allocate it. If present, dir specifies
170 the inode number of the directory which the inode is to be
171 located. The second optional argument mode specifies the per‐
172 missions of the new inode. (If the directory bit is set on the
173 mode, the allocation routine will function differently.) Also
174 available as ffi.
175 freeb block [count]
177 Mark the block number block as not allocated. If the optional
178 argument count is present, then count blocks starting at block
179 number block will be marked as not allocated.
180 freefrag [-c chunk_kb]
182 Report free space fragmentation on the currently open file sys‐
183 tem. If the -c option is specified then the filefrag command
184 will print how many free chunks of size chunk_kb can be found in
185 the file system. The chunk size must be a power of two and be
186 larger than the file system block size.
187 freei filespec [num]
189 Free the inode specified by filespec. If num is specified, also
190 clear num-1 inodes after the specified inode.
191 help Print a list of commands understood by debugfs.
193 htree_dump filespec
195 Dump the hash-indexed directory filespec, showing its tree
196 structure.
197 icheck block ...
199 Print a listing of the inodes which use the one or more blocks
200 specified on the command line.
201 imap filespec
203 Print the location of the inode data structure (in the inode ta‐
204 ble) of the inode filespec.
205 init_filesys device blocksize
207 Create an ext2 file system on device with device size blocksize.
208 Note that this does not fully initialize all of the data struc‐
209 tures; to do this, use the mke2fs(8) program. This is just a
210 call to the low-level library, which sets up the superblock and
211 block descriptors.
212 kill_file filespec
214 Deallocate the inode filespec and its blocks. Note that this
215 does not remove any directory entries (if any) to this inode.
216 See the rm(1) command if you wish to unlink a file.
217 lcd directory
219 Change the current working directory of the debugfs process to
220 directory on the native filesystem.
221 ln filespec dest_file
223 Create a link named dest_file which is a hard link to filespec.
224 Note this does not adjust the inode reference counts.
225 logdump [-acs] [-b block] [-i filespec] [-f journal_file] [output_file]
227 Dump the contents of the ext3 journal. By default, dump the
228 journal inode as specified in the superblock. However, this can
229 be overridden with the -i option, which dumps the journal from
230 the internal inode given by filespec. A regular file containing
231 journal data can be specified using the -f option. Finally, the
232 -s option utilizes the backup information in the superblock to
233 locate the journal.
234 The -a option causes the logdump program to print the contents
236 of all of the descriptor blocks. The -b option causes logdump
237 to print all journal records that are refer to the specified
238 block. The -c option will print out the contents of all of the
239 data blocks selected by the -a and -b options.
240 ls [-d] [-l] [-p] filespec
242 Print a listing of the files in the directory filespec. The -d
243 flag will list deleted entries in the directory. The -l flag
244 will list files using a more verbose format. The -p flag will
245 list the files in a format which is more easily parsable by
246 scripts, as well as making it more clear when there are spaces
247 or other non-printing characters at the end of filenames.
248 list_deleted_inodes [limit]
250 List deleted inodes, optionally limited to those deleted within
251 limit seconds ago. Also available as lsdel.
252 This command was useful for recovering from accidental file
254 deletions for ext2 file systems. Unfortunately, it is not use‐
255 ful for this purpose if the files were deleted using ext3 or
256 ext4, since the inode's data blocks are no longer available
257 after the inode is released.
258 modify_inode filespec
260 Modify the contents of the inode structure in the inode file‐
261 spec. Also available as mi.
262 mkdir filespec
264 Make a directory.
265 mknod filespec [p|[[c|b] major minor]]
267 Create a special device file (a named pipe, character or block
268 device). If a character or block device is to be made, the
269 major and minor device numbers must be specified.
270 ncheck [-c] inode_num ...
272 Take the requested list of inode numbers, and print a listing of
273 pathnames to those inodes. The -c flag will enable checking the
274 file type information in the directory entry to make sure it
275 matches the inode's type.
276 open [-weficD] [-b blocksize] [-s superblock] device
278 Open a filesystem for editing. The -f flag forces the filesys‐
279 tem to be opened even if there are some unknown or incompatible
280 filesystem features which would normally prevent the filesystem
281 from being opened. The -e flag causes the filesystem to be
282 opened in exclusive mode. The -b, -c, -i, -s, -w, and -D
283 options behave the same as the command-line options to debugfs.
284 punch filespec start_blk [end_blk]
286 Delete the blocks in the inode ranging from start_blk to
287 end_blk. If end_blk is omitted then this command will function
288 as a truncate command; that is, all of the blocks starting at
289 start_blk through to the end of the file will be deallocated.
290 symlink filespec target
292 Make a symbolic link.
293 pwd Print the current working directory.
295 quit Quit debugfs
297 rdump directory destination
299 Recursively dump directory and all its contents (including regu‐
300 lar files, symbolic links, and other directories) into the named
301 destination which should be an existing directory on the native
302 filesystem.
303 rm pathname
305 Unlink pathname. If this causes the inode pointed to by path‐
306 name to have no other references, deallocate the file. This
307 command functions as the unlink() system call.
308 rmdir filespec
310 Remove the directory filespec.
311 setb block [count]
313 Mark the block number block as allocated. If the optional argu‐
314 ment count is present, then count blocks starting at block num‐
315 ber block will be marked as allocated.
316 set_block_group bgnum field value
318 Modify the block group descriptor specified by bgnum so that the
319 block group descriptor field field has value value. Also avail‐
320 able as set_bg.
321 seti filespec [num]
323 Mark inode filespec as in use in the inode bitmap. If num is
324 specified, also set num-1 inodes after the specified inode.
325 set_inode_field filespec field value
327 Modify the inode specified by filespec so that the inode field
328 field has value value. The list of valid inode fields which can
329 be set via this command can be displayed by using the command:
330 set_inode_field -l Also available as sif.
331 set_mmp_value field value
333 Modify the multiple-mount protection (MMP) data so that the MMP
334 field field has value value. The list of valid MMP fields which
335 can be set via this command can be displayed by using the com‐
336 mand: set_mmp_value -l Also available as smmp.
337 set_super_value field value
339 Set the superblock field field to value. The list of valid
340 superblock fields which can be set via this command can be dis‐
341 played by using the command: set_super_value -l Also available
342 as ssv.
343 show_super_stats [-h]
345 List the contents of the super block and the block group
346 descriptors. If the -h flag is given, only print out the
347 superblock contents. Also available as stats.
348 stat filespec
350 Display the contents of the inode structure of the inode file‐
351 spec.
352 testb block [count]
354 Test if the block number block is marked as allocated in the
355 block bitmap. If the optional argument count is present, then
356 count blocks starting at block number block will be tested.
357 testi filespec
359 Test if the inode filespec is marked as allocated in the inode
360 bitmap.
361 undel <inode_number> [pathname]
363 Undelete the specified inode number (which must be surrounded by
364 angle brackets) so that it and its blocks are marked in use, and
365 optionally link the recovered inode to the specified pathname.
366 The e2fsck command should always be run after using the undel
367 command to recover deleted files.
368 Note that if you are recovering a large number of deleted files,
370 linking the inode to a directory may require the directory to be
371 expanded, which could allocate a block that had been used by one
372 of the yet-to-be-undeleted files. So it is safer to undelete
373 all of the inodes without specifying a destination pathname, and
374 then in a separate pass, use the debugfs link command to link
375 the inode to the destination pathname, or use e2fsck to check
376 the filesystem and link all of the recovered inodes to the
377 lost+found directory.
378 unlink pathname
380 Remove the link specified by pathname to an inode. Note this
381 does not adjust the inode reference counts.
382 write source_file out_file
384 Copy the contents of source_file into a newly-created file in
385 the filesystem named out_file.
386 zap_block [-f filespec] [-o offset] [-l length] [-p pattern] block_num
388 Overwrite the block specified by
390 block_num with zero (NUL) bytes, or if -p is given use the byte
391 specified by pattern. If -f is given then block_num is relative
392 to the start of the file given by filespec. The -o and -l
393 options limit the range of bytes to zap to the specified offset
394 and length relative to the start of the block.
395 zap_block [-f filespec] [-b bit] block_num
397 Bit-flip portions of the physical block_num. If -f is given,
398 then block_num is a logical block relative to the start of file‐
399 spec.
400
402 DEBUGFS_PAGER, PAGER
403 The debugfs program always pipes the output of the some commands
404 through a pager program. These commands include:
405 show_super_stats (stats), list_directory (ls), show_inode_info
406 (stat), list_deleted_inodes (lsdel), and htree_dump. The spe‐
407 cific pager can explicitly specified by the DEBUGFS_PAGER envi‐
408 ronment variable, and if it is not set, by the PAGER environment
409 variable.
410 Note that since a pager is always used, the less(1) pager is not
412 particularly appropriate, since it clears the screen before dis‐
413 playing the output of the command and clears the output the
414 screen when the pager is exited. Many users prefer to use the
415 less(1) pager for most purposes, which is why the DEBUGFS_PAGER
416 environment variable is available to override the more general
417 PAGER environment variable.
418
420 debugfs was written by Theodore Ts'o <tytso@mit.edu>.
421
423 dumpe2fs(8), tune2fs(8), e2fsck(8), mke2fs(8), ext4(5)
424E2fsprogs version 1.42.9 December 2013 DEBUGFS(8)