1xfs_db(8) System Manager's Manual xfs_db(8)
2
6 xfs_db - debug an XFS filesystem
7
9 xfs_db [ -c cmd ] ... [ -i|r|x|F ] [ -f ] [ -l logdev ] [ -p progname ]
10 device
11 xfs_db -V
12
14 xfs_db is used to examine an XFS filesystem. Under rare circumstances
15 it can also be used to modify an XFS filesystem, but that task is nor‐
16 mally left to xfs_repair(8) or to scripts such as xfs_admin(8) that run
17 xfs_db.
18
20 -c cmd xfs_db commands may be run interactively (the default) or as ar‐
21 guments on the command line. Multiple -c arguments may be given.
22 The commands are run in the sequence given, then the program ex‐
23 its.
24 -f Specifies that the filesystem image to be processed is stored in
26 a regular file at device (see the mkfs.xfs(8) -d file option).
27 This might happen if an image copy of a filesystem has been made
28 into an ordinary file with xfs_copy(8).
29 -F Specifies that we want to continue even if the superblock magic
31 is not correct. For use in xfs_metadump.
32 -i Allows execution on a mounted filesystem, provided it is mounted
34 read-only. Useful for shell scripts which must only operate on
35 filesystems in a guaranteed consistent state (either unmounted
36 or mounted read-only). These semantics are slightly different to
37 that of the -r option.
38 -l logdev
40 Specifies the device where the filesystems external log resides.
41 Only for those filesystems which use an external log. See the
42 mkfs.xfs(8) -l option, and refer to xfs(5) for a detailed de‐
43 scription of the XFS log.
44 -p progname
46 Set the program name to progname for prompts and some error mes‐
47 sages, the default value is xfs_db.
48 -r Open device or filename read-only. This option is required if
50 the filesystem is mounted. It is only necessary to omit this
51 flag if a command that changes data (write, blocktrash, crc) is
52 to be used.
53 -x Specifies expert mode. This enables the (write, blocktrash, crc
55 invalidate/revalidate) commands.
56 -V Prints the version number and exits.
58
60 xfs_db commands can be broken up into two classes. Most commands are
61 for the navigation and display of data structures in the filesystem.
62 Other commands are for scanning the filesystem in some way.
63 Commands which are used to navigate the filesystem structure take argu‐
65 ments which reflect the names of filesystem structure fields. There
66 can be multiple field names separated by dots when the underlying
67 structures are nested, as in C. The field names can be indexed (as an
68 array index) if the underlying field is an array. The array indices
69 can be specified as a range, two numbers separated by a dash.
70 xfs_db maintains a current address in the filesystem. The granularity
72 of the address is a filesystem structure. This can be a filesystem
73 block, an inode or quota (smaller than a filesystem block), or a direc‐
74 tory block (could be larger than a filesystem block). There are a va‐
75 riety of commands to set the current address. Associated with the cur‐
76 rent address is the current data type, which is the structural type of
77 this data. Commands which follow the structure of the filesystem al‐
78 ways set the type as well as the address. Commands which examine
79 pieces of an individual file (inode) need the current inode to be set,
80 this is done with the inode command.
81 The current address/type information is actually maintained in a stack
83 that can be explicitly manipulated with the push, pop, and stack com‐
84 mands. This allows for easy examination of a nested filesystem struc‐
85 ture. Also, the last several locations visited are stored in a ring
86 buffer which can be manipulated with the forward, back, and ring com‐
87 mands.
88 XFS filesystems are divided into a small number of allocation groups.
90 xfs_db maintains a notion of the current allocation group which is ma‐
91 nipulated by some commands. The initial allocation group is 0.
92
94 Many commands have extensive online help. Use the help command for more
95 details on any command.
96 a See the addr command.
98 ablock filoff
100 Set current address to the offset filoff (a filesystem block
101 number) in the attribute area of the current inode.
102 addr [field-expression]
104 Set current address to the value of the field-expression. This
105 is used to "follow" a reference in one structure to the object
106 being referred to. If no argument is given, the current address
107 is printed.
108 agf [agno]
110 Set current address to the AGF block for allocation group agno.
111 If no argument is given, use the current allocation group.
112 agfl [agno]
114 Set current address to the AGFL block for allocation group agno.
115 If no argument is given, use the current allocation group.
116 agi [agno]
118 Set current address to the AGI block for allocation group agno.
119 If no argument is given, use the current allocation group.
120 agresv [agno]
122 Displays the length, free block count, per-AG reservation size,
123 and per-AG reservation usage for a given AG. If no argument is
124 given, display information for all AGs.
125 attr_remove [-r|-u|-s] [-n] name
127 Remove the specified extended attribute from the current file.
128 -r Sets the attribute in the root namespace. Only one name‐
130 space option can be specified.
131 -u Sets the attribute in the user namespace. Only one name‐
133 space option can be specified.
134 -s Sets the attribute in the secure namespace. Only one
136 namespace option can be specified.
137 -n Do not enable 'noattr2' mode on V4 filesystems.
139 attr_set [-r|-u|-s] [-n] [-R|-C] [-v namelen] name
141 Sets an extended attribute on the current file with the given
142 name.
143 -r Sets the attribute in the root namespace. Only one name‐
145 space option can be specified.
146 -u Sets the attribute in the user namespace. Only one name‐
148 space option can be specified.
149 -s Sets the attribute in the secure namespace. Only one
151 namespace option can be specified.
152 -n Do not enable 'noattr2' mode on V4 filesystems.
154 -R Replace the attribute. The command will fail if the at‐
156 tribute does not already exist.
157 -C Create the attribute. The command will fail if the at‐
159 tribute already exists.
160 -v Set the attribute value to a string of this length con‐
162 taining the letter 'v'.
163 b See the back command.
165 back Move to the previous location in the position ring.
167 blockfree
169 Free block usage information collected by the last execution of
170 the blockget command. This must be done before another blockget
171 command can be given, presumably with different arguments than
172 the previous one.
173 blockget [-npvs] [-b bno] ... [-i ino] ...
175 Get block usage and check filesystem consistency. The informa‐
176 tion is saved for use by a subsequent blockuse, ncheck, or
177 blocktrash command.
178 -b is used to specify filesystem block numbers about which
180 verbose information should be printed.
181 -i is used to specify inode numbers about which verbose in‐
183 formation should be printed.
184 -n is used to save pathnames for inodes visited, this is
186 used to support the xfs_ncheck(8) command. It also means
187 that pathnames will be printed for inodes that have prob‐
188 lems. This option uses a lot of memory so is not enabled
189 by default.
190 -p causes error messages to be prefixed with the filesystem
192 name being processed. This is useful if several copies of
193 xfs_db are run in parallel.
194 -s restricts output to severe errors only. This is useful if
196 the output is too long otherwise.
197 -v enables verbose output. Messages will be printed for ev‐
199 ery block and inode processed.
200 blocktrash [-z] [-o offset] [-n count] [-x min] [-y max] [-s seed]
202 [-0|1|2|3] [-t type] ...
203 Trash randomly selected filesystem metadata blocks. Trashing
204 occurs to randomly selected bits in the chosen blocks. This
205 command is available only in debugging versions of xfs_db. It
206 is useful for testing xfs_repair(8).
207 -0 | -1 | -2 | -3
209 These are used to set the operating mode for blocktrash.
210 Only one can be used: -0 changed bits are cleared; -1
211 changed bits are set; -2 changed bits are inverted; -3
212 changed bits are randomized.
213 -n supplies the count of block-trashings to perform (default
215 1).
216 -o supplies the bit offset at which to start trashing the
218 block. If the value is preceded by a '+', the trashing
219 will start at a randomly chosen offset that is larger
220 than the value supplied. The default is to randomly
221 choose an offset anywhere in the block.
222 -s supplies a seed to the random processing.
224 -t gives a type of blocks to be selected for trashing. Mul‐
226 tiple -t options may be given. If no -t options are given
227 then all metadata types can be trashed.
228 -x sets the minimum size of bit range to be trashed. The de‐
230 fault value is 1.
231 -y sets the maximum size of bit range to be trashed. The de‐
233 fault value is 1024.
234 -z trashes the block at the top of the stack. It is not
236 necessary to run blockget if this option is supplied.
237 blockuse [-n] [-c count]
239 Print usage for current filesystem block(s). For each block,
240 the type and (if any) inode are printed.
241 -c specifies a count of blocks to process. The default value
243 is 1 (the current block only).
244 -n specifies that file names should be printed. The prior
246 blockget command must have also specified the -n option.
247 bmap [-a] [-d] [block [len]]
249 Show the block map for the current inode. The map display can
250 be restricted to an area of the file with the block and len ar‐
251 guments. If block is given and len is omitted then 1 is assumed
252 for len.
253 The -a and -d options are used to select the attribute or data
255 area of the inode, if neither option is given then both areas
256 are shown.
257 btdump [-a] [-i]
259 If the cursor points to a btree node, dump the btree from that
260 block downward. If instead the cursor points to an inode, dump
261 the data fork block mapping btree if there is one. If the cur‐
262 sor points to a directory or extended attribute btree node, dump
263 that. By default, only records stored in the btree are dumped.
264 -a If the cursor points at an inode, dump the extended at‐
266 tribute block mapping btree, if present.
267 -i Dump all keys and pointers in intermediate btree nodes,
269 and all records in leaf btree nodes.
270 btheight [-b blksz] [-n recs] [-w max|-w min] btree types...
272 For a given number of btree records and a btree type, report the
273 number of records and blocks for each level of the btree, and
274 the total number of blocks. The btree type must be given after
275 the options.
276 A raw btree geometry can be provided in the format
278 "record_bytes:key_bytes:ptr_bytes:header_type", where
279 header_type is one of "short", "long", "shortcrc", or "longcrc".
280 The supported btree types are: bnobt, cntbt, inobt, finobt,
282 bmapbt, refcountbt, and rmapbt.
283 Options are as follows:
285 -b is used to override the btree block size. The default is
287 the filesystem block size.
288 -n is used to specify the number of records to store. This
290 argument is required.
291 -w max
293 shows only the best case scenario, which is when the
294 btree blocks are maximally loaded.
295 -w min
297 shows only the worst case scenario, which is when the
298 btree blocks are half full.
299 check See the blockget command.
301 convert type number [type number] ... type
303 Convert from one address form to another. The known types, with
304 alternate names, are:
305 agblock or agbno (filesystem block within an allocation
306 group)
307 agino or aginode (inode number within an allocation group)
308 agnumber or agno (allocation group number)
309 bboff or daddroff (byte offset in a daddr)
310 blkoff or fsboff or agboff (byte offset in a agblock or fs‐
311 block)
312 byte or fsbyte (byte address in filesystem)
313 daddr or bb (disk address, 512-byte blocks)
314 fsblock or fsb or fsbno (filesystem block, see the fsblock
315 command)
316 ino or inode (inode number)
317 inoidx or offset (index of inode in filesystem block)
318 inooff or inodeoff (byte offset in inode)
319 Only conversions that "make sense" are allowed. The compound
321 form (with more than three arguments) is useful for conversions
322 such as convert agno ag agbno agb fsblock.
323 crc [-i|-r|-v]
325 Invalidates, revalidates, or validates the CRC (checksum) field
326 of the current structure, if it has one. This command is avail‐
327 able only on CRC-enabled filesystems. With no argument, valida‐
328 tion is performed. Each command will display the resulting CRC
329 value and state.
330 -i Invalidate the structure's CRC value (incrementing it by
332 one), and write it to disk.
333 -r Recalculate the current structure's correct CRC value,
335 and write it to disk.
336 -v Validate and display the current value and state of the
338 structure's CRC.
339 daddr [d]
341 Set current address to the daddr (512 byte block) given by d.
342 If no value for d is given, the current address is printed, ex‐
343 pressed as a daddr. The type is set to data (uninterpreted).
344 dblock filoff
346 Set current address to the offset filoff (a filesystem block
347 number) in the data area of the current inode.
348 debug [flagbits]
350 Set debug option bits. These are used for debugging xfs_db. If
351 no value is given for flagbits, print the current debug option
352 bits. These are for the use of the implementor.
353 dquot [-g|-p|-u] id
355 Set current address to a group, project or user quota block for
356 the given ID. Defaults to user quota.
357 echo [arg] ...
359 Echo the arguments to the output.
360 f See the forward command.
362 forward
364 Move forward to the next entry in the position ring.
365 frag [-adflqRrv]
367 Get file fragmentation data. This prints information about frag‐
368 mentation of file data in the filesystem (as opposed to fragmen‐
369 tation of freespace, for which see the freesp command). Every
370 file in the filesystem is examined to see how far from ideal its
371 extent mappings are. A summary is printed giving the totals.
372 -v sets verbosity, every inode has information printed for
374 it. The remaining options select which inodes and ex‐
375 tents are examined. If no options are given then all are
376 assumed set, otherwise just those given are enabled.
377 -a enables processing of attribute data.
379 -d enables processing of directory data.
381 -f enables processing of regular file data.
383 -l enables processing of symbolic link data.
385 -q enables processing of quota file data.
387 -R enables processing of realtime control file data.
389 -r enables processing of realtime file data.
391 freesp [-bcds] [-A alignment] [-a ag] ... [-e i] [-h h1] ... [-m m]
393 Summarize free space for the filesystem. The free blocks are ex‐
394 amined and totalled, and displayed in the form of a histogram,
395 with a count of extents in each range of free extent sizes.
396 -A reports only free extents with starting blocks aligned to
398 alignment blocks.
399 -a adds ag to the list of allocation groups to be processed.
401 If no -a options are given then all allocation groups are
402 processed.
403 -b specifies that the histogram buckets are binary-sized,
405 with the starting sizes being the powers of 2.
406 -c specifies that freesp will search the by-size (cnt) space
408 Btree instead of the default by-block (bno) space Btree.
409 -d specifies that every free extent will be displayed.
411 -e specifies that the histogram buckets are equal-sized,
413 with the size specified as i.
414 -h specifies a starting block number for a histogram bucket
416 as h1. Multiple -h's are given to specify the complete
417 set of buckets.
418 -m specifies that the histogram starting block numbers are
420 powers of m. This is the general case of -b.
421 -s specifies that a final summary of total free extents,
423 free blocks, and the average free extent size is printed.
424 fsb See the fsblock command.
426 fsblock [fsb]
428 Set current address to the fsblock value given by fsb. If no
429 value for fsb is given the current address is printed, expressed
430 as an fsb. The type is set to data (uninterpreted). XFS
431 filesystem block numbers are computed ((agno << agshift) | ag‐
432 block) where agshift depends on the size of an allocation group.
433 Use the convert command to convert to and from this form. Block
434 numbers given for file blocks (for instance from the bmap com‐
435 mand) are in this form.
436 fsmap [ start ] [ end ]
438 Prints the mapping of disk blocks used by an XFS filesystem.
439 The map lists each extent used by files, allocation group meta‐
440 data, journalling logs, and static filesystem metadata, as well
441 as any regions that are unused. All blocks, offsets, and
442 lengths are specified in units of 512-byte blocks, no matter
443 what the filesystem's block size is. The optional start and end
444 arguments can be used to constrain the output to a particular
445 range of disk blocks.
446 fuzz [-c] [-d] field action
448 Write garbage into a specific structure field on disk. Expert
449 mode must be enabled to use this command. The operation happens
450 immediately; there is no buffering.
451 The fuzz command can take the following actions against a field:
453 zeroes
455 Clears all bits in the field.
456 ones
458 Sets all bits in the field.
459 firstbit
461 Flips the first bit in the field. For a scalar value,
462 this is the highest bit.
463 middlebit
465 Flips the middle bit in the field.
466 lastbit
468 Flips the last bit in the field. For a scalar value,
469 this is the lowest bit.
470 add Adds a small value to a scalar field.
472 sub Subtracts a small value from a scalar field.
474 random
476 Randomizes the contents of the field.
477 The following switches affect the write behavior:
479 -c Skip write verifiers and CRC recalculation; allows in‐
481 valid data to be written to disk.
482 -d Skip write verifiers but perform CRC recalculation; al‐
484 lows invalid data to be written to disk to test detection
485 of invalid data.
486 hash string
488 Prints the hash value of string using the hash function of the
489 XFS directory and attribute implementation.
490 help [command]
492 Print help for one or all commands.
493 info Displays selected geometry information about the filesystem.
495 The output will have the same format that mkfs.xfs(8) prints
496 when creating a filesystem or xfs_info(8) prints when querying a
497 filesystem.
498 inode [inode#]
500 Set the current inode number. If no inode# is given, print the
501 current inode number.
502 label [label]
504 Set the filesystem label. The filesystem label can be used by
505 mount(8) instead of using a device special file. The maximum
506 length of an XFS label is 12 characters - use of a longer label
507 will result in truncation and a warning will be issued. If no
508 label is given, the current filesystem label is printed.
509 log [stop | start filename]
511 Start logging output to filename, stop logging, or print the
512 current logging status.
513 logformat [-c cycle] [-s sunit]
515 Reformats the log to the specified log cycle and log stripe
516 unit. This has the effect of clearing the log destructively.
517 If the log cycle is not specified, the log is reformatted to the
518 current cycle. If the log stripe unit is not specified, the
519 stripe unit from the filesystem superblock is used.
520 logres Print transaction reservation size information for each transac‐
522 tion type. This makes it easier to find discrepancies in the
523 reservation calculations between xfsprogs and the kernel, which
524 will help when diagnosing minimum log size calculation errors.
525 metadump [-egow] filename
527 Dumps metadata to a file. See xfs_metadump(8) for more informa‐
528 tion.
529 ncheck [-s] [-i ino] ...
531 Print name-inode pairs. A blockget -n command must be run first
532 to gather the information.
533 -i specifies an inode number to be printed. If no -i options
535 are given then all inodes are printed.
536 -s specifies that only setuid and setgid files are printed.
538 p See the print command.
540 pop Pop location from the stack.
542 print [field-expression] ...
544 Print field values. If no argument is given, print all fields
545 in the current structure.
546 push [command]
548 Push location to the stack. If command is supplied, set the cur‐
549 rent location to the results of command after pushing the old
550 location.
551 q See the quit command.
553 quit Exit xfs_db.
555 ring [index]
557 Show position ring (if no index argument is given), or move to a
558 specific entry in the position ring given by index.
559 sb [agno]
561 Set current address to SB header in allocation group agno. If
562 no agno is given, use the current allocation group number.
563 source source-file
565 Process commands from source-file. source commands can be
566 nested.
567 stack View the location stack.
569 type [type]
571 Set the current data type to type. If no argument is given,
572 show the current data type. The possible data types are: agf,
573 agfl, agi, attr, bmapbta, bmapbtd, bnobt, cntbt, data, dir,
574 dir2, dqblk, inobt, inode, log, refcntbt, rmapbt, rtbitmap, rt‐
575 summary, sb, symlink and text. See the TYPES section below for
576 more information on these data types.
577 timelimit [OPTIONS]
579 Print the minimum and maximum supported values for inode time‐
580 stamps, quota expiration timers, and quota grace periods sup‐
581 ported by this filesystem. Options include:
582 --bigtime
584 Print the time limits of an XFS filesystem with the big‐
585 time feature enabled.
586 --classic
588 Print the time limits of a classic XFS filesystem.
589 --compact
591 Print all limits as raw values on a single line.
592 --pretty
594 Print the timestamps in the current locale's date and
595 time format instead of raw seconds since the Unix epoch.
596 uuid [uuid | generate | rewrite | restore]
598 Set the filesystem universally unique identifier (UUID). The
599 filesystem UUID can be used by mount(8) instead of using a de‐
600 vice special file. The uuid can be set directly to the desired
601 UUID, or it can be automatically generated using the generate
602 option. These options will both write the UUID into every copy
603 of the superblock in the filesystem. On a CRC-enabled filesys‐
604 tem, this will set an incompatible superblock flag, and the
605 filesystem will not be mountable with older kernels. This can
606 be reverted with the restore option, which will copy the origi‐
607 nal UUID back into place and clear the incompatible flag as
608 needed. rewrite copies the current UUID from the primary su‐
609 perblock to all secondary copies of the superblock. If no argu‐
610 ment is given, the current filesystem UUID is printed.
611 version [feature | versionnum features2]
613 Enable selected features for a filesystem (certain features can
614 be enabled on an unmounted filesystem, after mkfs.xfs(8) has
615 created the filesystem). Support for unwritten extents can be
616 enabled using the extflg option. Support for version 2 log for‐
617 mat can be enabled using the log2 option. Support for extended
618 attributes can be enabled using the attr1 or attr2 option. Once
619 enabled, extended attributes cannot be disabled, but the user
620 may toggle between attr1 and attr2 at will (older kernels may
621 not support the newer version).
622 If no argument is given, the current version and feature bits
624 are printed. With one argument, this command will write the up‐
625 dated version number into every copy of the superblock in the
626 filesystem. If two arguments are given, they will be used as
627 numeric values for the versionnum and features2 bits respec‐
628 tively, and their string equivalent reported (but no modifica‐
629 tions are made).
630 write [-c|-d] [field value] ...
632 Write a value to disk. Specific fields can be set in structures
633 (struct mode), or a block can be set to data values (data mode),
634 or a block can be set to string values (string mode, for symlink
635 blocks). The operation happens immediately: there is no buffer‐
636 ing.
637 Struct mode is in effect when the current type is structural,
639 i.e. not data. For struct mode, the syntax is "write field
640 value".
641 Data mode is in effect when the current type is data. In this
643 case the contents of the block can be shifted or rotated left or
644 right, or filled with a sequence, a constant value, or a random
645 value. In this mode write with no arguments gives more informa‐
646 tion on the allowed commands.
647 -c Skip write verifiers and CRC recalculation; allows in‐
649 valid data to be written to disk.
650 -d Skip write verifiers but perform CRC recalculation. This
652 allows invalid data to be written to disk to test detec‐
653 tion of invalid data. (This is not possible for some
654 types.)
655
657 This section gives the fields in each structure type and their mean‐
658 ings. Note that some types of block cover multiple actual structures,
659 for instance directory blocks.
660 agf The AGF block is the header for block allocation information;
662 it is in the second 512-byte block of each allocation group.
663 The following fields are defined:
664 magicnum AGF block magic number, 0x58414746 ('XAGF').
665 versionnum version number, currently 1.
666 seqno sequence number starting from 0.
667 length size in filesystem blocks of the allocation
668 group. All allocation groups except the last
669 one of the filesystem have the superblock's
670 agblocks value here.
671 bnoroot block number of the root of the Btree holding
672 free space information sorted by block num‐
673 ber.
674 cntroot block number of the root of the Btree holding
675 free space information sorted by block count.
676 bnolevel number of levels in the by-block-number
677 Btree.
678 cntlevel number of levels in the by-block-count Btree.
679 flfirst index into the AGFL block of the first active
680 entry.
681 fllast index into the AGFL block of the last active
682 entry.
683 flcount count of active entries in the AGFL block.
684 freeblks count of blocks represented in the freespace
685 Btrees.
686 longest longest free space represented in the
687 freespace Btrees.
688 btreeblks number of blocks held in the AGF Btrees.
689 agfl The AGFL block contains block numbers for use of the block
691 allocator; it is in the fourth 512-byte block of each alloca‐
692 tion group. Each entry in the active list is a block number
693 within the allocation group that can be used for any purpose
694 if space runs low. The AGF block fields flfirst, fllast, and
695 flcount designate which entries are currently active. Entry
696 space is allocated in a circular manner within the AGFL
697 block. Fields defined:
698 bno array of all block numbers. Even those which
699 are not active are printed.
700 agi The AGI block is the header for inode allocation information;
702 it is in the third 512-byte block of each allocation group.
703 Fields defined:
704 magicnum AGI block magic number, 0x58414749 ('XAGI').
705 versionnum version number, currently 1.
706 seqno sequence number starting from 0.
707 length size in filesystem blocks of the allocation
708 group.
709 count count of inodes allocated.
710 root block number of the root of the Btree holding
711 inode allocation information.
712 level number of levels in the inode allocation
713 Btree.
714 freecount count of allocated inodes that are not in
715 use.
716 newino last inode number allocated.
717 dirino unused.
718 unlinked an array of inode numbers within the alloca‐
719 tion group. The entries in the AGI block are
720 the heads of lists which run through the in‐
721 ode next_unlinked field. These inodes are to
722 be unlinked the next time the filesystem is
723 mounted.
724 attr An attribute fork is organized as a Btree with the actual
726 data embedded in the leaf blocks. The root of the Btree is
727 found in block 0 of the fork. The index (sort order) of the
728 Btree is the hash value of the attribute name. All the
729 blocks contain a blkinfo structure at the beginning, see type
730 dir for a description. Nonleaf blocks are identical in format
731 to those for version 1 and version 2 directories, see type
732 dir for a description. Leaf blocks can refer to "local" or
733 "remote" attribute values. Local values are stored directly
734 in the leaf block. Leaf blocks contain the following fields:
735 hdr header containing a blkinfo structure info
736 (magic number 0xfbee), a count of active en‐
737 tries, usedbytes total bytes of names and
738 values, the firstused byte in the name area,
739 holes set if the block needs compaction, and
740 array freemap as for dir leaf blocks.
741 entries array of structures containing a hashval,
742 nameidx (index into the block of the name),
743 and flags incomplete, root, and local.
744 nvlist array of structures describing the attribute
745 names and values. Fields always present: val‐
746 uelen (length of value in bytes), namelen,
747 and name. Fields present for local values:
748 value (value string). Fields present for re‐
749 mote values: valueblk (fork block number of
750 containing the value).
751 Remote values are stored in an independent block in the at‐
753 tribute fork. Prior to v5, value blocks had no structure,
754 but in v5 they acquired a header structure with the following
755 fields:
756 magic attr3 remote block magic number, 0x5841524d
757 ('XARM').
758 offset Byte offset of this data block within the
759 overall attribute value.
760 bytes Number of bytes stored in this block.
761 crc Checksum of the attribute block contents.
762 uuid Filesystem UUID.
763 owner Inode that owns this attribute value.
764 bno Block offset of this block within the inode's
765 attribute fork.
766 lsn Log serial number of the last time this block
767 was logged.
768 data The attribute value data.
769 bmapbt Files with many extents in their data or attribute fork will
771 have the extents described by the contents of a Btree for
772 that fork, instead of being stored directly in the inode.
773 Each bmap Btree starts with a root block contained within the
774 inode. The other levels of the Btree are stored in filesys‐
775 tem blocks. The blocks are linked to sibling left and right
776 blocks at each level, as well as by pointers from parent to
777 child blocks. Each block contains the following fields:
778 magic bmap Btree block magic number, 0x424d4150
779 ('BMAP').
780 level level of this block above the leaf level.
781 numrecs number of records or keys in the block.
782 leftsib left (logically lower) sibling block, 0 if
783 none.
784 rightsib right (logically higher) sibling block, 0 if
785 none.
786 recs [leaf blocks only] array of extent records.
787 Each record contains startoff, startblock,
788 blockcount, and extentflag (1 if the extent
789 is unwritten).
790 keys [non-leaf blocks only] array of key records.
791 These are the first key value of each block
792 in the level below this one. Each record con‐
793 tains startoff.
794 ptrs [non-leaf blocks only] array of child block
795 pointers. Each pointer is a filesystem block
796 number to the next level in the Btree.
797 bnobt There is one set of filesystem blocks forming the by-block-
799 number allocation Btree for each allocation group. The root
800 block of this Btree is designated by the bnoroot field in the
801 corresponding AGF block. The blocks are linked to sibling
802 left and right blocks at each level, as well as by pointers
803 from parent to child blocks. Each block has the following
804 fields:
805 magic BNOBT block magic number, 0x41425442
806 ('ABTB').
807 level level number of this block, 0 is a leaf.
808 numrecs number of data entries in the block.
809 leftsib left (logically lower) sibling block, 0 if
810 none.
811 rightsib right (logically higher) sibling block, 0 if
812 none.
813 recs [leaf blocks only] array of freespace
814 records. Each record contains startblock and
815 blockcount.
816 keys [non-leaf blocks only] array of key records.
817 These are the first value of each block in
818 the level below this one. Each record con‐
819 tains startblock and blockcount.
820 ptrs [non-leaf blocks only] array of child block
821 pointers. Each pointer is a block number
822 within the allocation group to the next level
823 in the Btree.
824 cntbt There is one set of filesystem blocks forming the by-block-
826 count allocation Btree for each allocation group. The root
827 block of this Btree is designated by the cntroot field in the
828 corresponding AGF block. The blocks are linked to sibling
829 left and right blocks at each level, as well as by pointers
830 from parent to child blocks. Each block has the following
831 fields:
832 magic CNTBT block magic number, 0x41425443
833 ('ABTC').
834 level level number of this block, 0 is a leaf.
835 numrecs number of data entries in the block.
836 leftsib left (logically lower) sibling block, 0 if
837 none.
838 rightsib right (logically higher) sibling block, 0 if
839 none.
840 recs [leaf blocks only] array of freespace
841 records. Each record contains startblock and
842 blockcount.
843 keys [non-leaf blocks only] array of key records.
844 These are the first value of each block in
845 the level below this one. Each record con‐
846 tains blockcount and startblock.
847 ptrs [non-leaf blocks only] array of child block
848 pointers. Each pointer is a block number
849 within the allocation group to the next level
850 in the Btree.
851 data User file blocks, and other blocks whose type is unknown,
853 have this type for display purposes in xfs_db. The block
854 data is displayed in hexadecimal format.
855 dir A version 1 directory is organized as a Btree with the direc‐
857 tory data embedded in the leaf blocks. The root of the Btree
858 is found in block 0 of the file. The index (sort order) of
859 the Btree is the hash value of the entry name. All the blocks
860 contain a blkinfo structure at the beginning with the follow‐
861 ing fields:
862 forw next sibling block.
863 back previous sibling block.
864 magic magic number for this block type.
865 The non-leaf (node) blocks have the following fields:
866 hdr header containing a blkinfo structure info
867 (magic number 0xfebe), the count of active
868 entries, and the level of this block above
869 the leaves.
870 btree array of entries containing hashval and be‐
871 fore fields. The before value is a block num‐
872 ber within the directory file to the child
873 block, the hashval is the last hash value in
874 that block.
875 The leaf blocks have the following fields:
876 hdr header containing a blkinfo structure info
877 (magic number 0xfeeb), the count of active
878 entries, namebytes (total name string bytes),
879 holes flag (block needs compaction), and
880 freemap (array of base, size entries for free
881 regions).
882 entries array of structures containing hashval,
883 nameidx (byte index into the block of the
884 name string), and namelen.
885 namelist array of structures containing inumber and
886 name.
887 dir2 A version 2 directory has four kinds of blocks. Data blocks
889 start at offset 0 in the file. There are two kinds of data
890 blocks: single-block directories have the leaf information
891 embedded at the end of the block, data blocks in multi-block
892 directories do not. Node and leaf blocks start at offset
893 32GiB (with either a single leaf block or the root node
894 block). Freespace blocks start at offset 64GiB. The node
895 and leaf blocks form a Btree, with references to the data in
896 the data blocks. The freespace blocks form an index of long‐
897 est free spaces within the data blocks.
898 A single-block directory block contains the following fields:
900 bhdr header containing magic number 0x58443242
901 ('XD2B') and an array bestfree of the longest
902 3 free spaces in the block (offset, length).
903 bu array of union structures. Each element is
904 either an entry or a freespace. For entries,
905 there are the following fields: inumber,
906 namelen, name, and tag. For freespace, there
907 are the following fields: freetag (0xffff),
908 length, and tag. The tag value is the byte
909 offset in the block of the start of the entry
910 it is contained in.
911 bleaf array of leaf entries containing hashval and
912 address. The address is a 64-bit word offset
913 into the file.
914 btail tail structure containing the total count of
915 leaf entries and stale count of unused leaf
916 entries.
917 A data block contains the following fields:
918 dhdr header containing magic number 0x58443244
919 ('XD2D') and an array bestfree of the longest
920 3 free spaces in the block (offset, length).
921 du array of union structures as for bu.
922 Leaf blocks have two possible forms. If the Btree consists of
923 a single leaf then the freespace information is in the leaf
924 block, otherwise it is in separate blocks and the root of the
925 Btree is a node block. A leaf block contains the following
926 fields:
927 lhdr header containing a blkinfo structure info
928 (magic number 0xd2f1 for the single leaf
929 case, 0xd2ff for the true Btree case), the
930 total count of leaf entries, and stale count
931 of unused leaf entries.
932 lents leaf entries, as for bleaf.
933 lbests [single leaf only] array of values which rep‐
934 resent the longest freespace in each data
935 block in the directory.
936 ltail [single leaf only] tail structure containing
937 bestcount count of lbests.
938 A node block is identical to that for types attr and dir.
939 A freespace block contains the following fields:
941 fhdr header containing magic number 0x58443246
942 ('XD2F'), firstdb first data block number
943 covered by this freespace block, nvalid num‐
944 ber of valid entries, and nused number of en‐
945 tries representing real data blocks.
946 fbests array of values as for lbests.
947 dqblk The quota information is stored in files referred to by the
949 superblock uquotino and pquotino fields. Each filesystem
950 block in a quota file contains a constant number of quota en‐
951 tries. The quota entry size is currently 136 bytes, so with a
952 4KiB filesystem block size there are 30 quota entries per
953 block. The dquot command is used to locate these entries in
954 the filesystem. The file entries are indexed by the user or
955 project identifier to determine the block and offset. Each
956 quota entry has the following fields:
957 magic magic number, 0x4451 ('DQ').
958 version version number, currently 1.
959 flags flags, values include 0x01 for user quota,
960 0x02 for project quota.
961 id user or project identifier.
962 blk_hardlimit absolute limit on blocks in use.
963 blk_softlimit preferred limit on blocks in use.
964 ino_hardlimit absolute limit on inodes in use.
965 ino_softlimit preferred limit on inodes in use.
966 bcount blocks actually in use.
967 icount inodes actually in use.
968 itimer time when service will be refused if soft
969 limit is violated for inodes.
970 btimer time when service will be refused if soft
971 limit is violated for blocks.
972 iwarns number of warnings issued about inode
973 limit violations.
974 bwarns number of warnings issued about block
975 limit violations.
976 rtb_hardlimit absolute limit on realtime blocks in use.
977 rtb_softlimit preferred limit on realtime blocks in use.
978 rtbcount realtime blocks actually in use.
979 rtbtimer time when service will be refused if soft
980 limit is violated for realtime blocks.
981 rtbwarns number of warnings issued about realtime
982 block limit violations.
983 inobt There is one set of filesystem blocks forming the inode allo‐
985 cation Btree for each allocation group. The root block of
986 this Btree is designated by the root field in the correspond‐
987 ing AGI block. The blocks are linked to sibling left and
988 right blocks at each level, as well as by pointers from par‐
989 ent to child blocks. Each block has the following fields:
990 magic INOBT block magic number, 0x49414254
991 ('IABT').
992 level level number of this block, 0 is a leaf.
993 numrecs number of data entries in the block.
994 leftsib left (logically lower) sibling block, 0 if
995 none.
996 rightsib right (logically higher) sibling block, 0 if
997 none.
998 recs [leaf blocks only] array of inode records.
999 Each record contains startino allocation-
1000 group relative inode number, freecount count
1001 of free inodes in this chunk, and free bit‐
1002 map, LSB corresponds to inode 0.
1003 keys [non-leaf blocks only] array of key records.
1004 These are the first value of each block in
1005 the level below this one. Each record con‐
1006 tains startino.
1007 ptrs [non-leaf blocks only] array of child block
1008 pointers. Each pointer is a block number
1009 within the allocation group to the next level
1010 in the Btree.
1011 inode Inodes are allocated in "chunks" of 64 inodes each. Usually a
1013 chunk is multiple filesystem blocks, although there are cases
1014 with large filesystem blocks where a chunk is less than one
1015 block. The inode Btree (see inobt above) refers to the inode
1016 numbers per allocation group. The inode numbers directly re‐
1017 flect the location of the inode block on disk. Use the inode
1018 command to point xfs_db to a specific inode. Each inode con‐
1019 tains four regions: core, next_unlinked, u, and a. core con‐
1020 tains the fixed information. next_unlinked is separated from
1021 the core due to journaling considerations, see type agi field
1022 unlinked. u is a union structure that is different in size
1023 and format depending on the type and representation of the
1024 file data ("data fork"). a is an optional union structure to
1025 describe attribute data, that is different in size, format,
1026 and location depending on the presence and representation of
1027 attribute data, and the size of the u data ("attribute
1028 fork"). xfs_db automatically selects the proper union mem‐
1029 bers based on information in the inode.
1030 The following are fields in the inode core:
1032 magic inode magic number, 0x494e ('IN').
1033 mode mode and type of file, as described in
1034 chmod(2), mknod(2), and stat(2).
1035 version inode version, 1 or 2.
1036 format format of u union data (0: xfs_dev_t, 1: lo‐
1037 cal file - in-inode directory or symlink, 2:
1038 extent list, 3: Btree root, 4: unique id [un‐
1039 used]).
1040 nlinkv1 number of links to the file in a version 1
1041 inode.
1042 nlinkv2 number of links to the file in a version 2
1043 inode.
1044 projid_lo owner's project id (low word; version 2 inode
1045 only). projid_hi owner's project id (high
1046 word; version 2 inode only).
1047 uid owner's user id.
1048 gid owner's group id.
1049 atime time last accessed (seconds and nanoseconds).
1050 mtime time last modified.
1051 ctime time created or inode last modified.
1052 size number of bytes in the file.
1053 nblocks total number of blocks in the file including
1054 indirect and attribute.
1055 extsize basic/minimum extent size for the file.
1056 nextents number of extents in the data fork.
1057 naextents number of extents in the attribute fork.
1058 forkoff attribute fork offset in the inode, in 64-bit
1059 words from the start of u.
1060 aformat format of a data (1: local attribute data, 2:
1061 extent list, 3: Btree root).
1062 dmevmask DMAPI event mask.
1063 dmstate DMAPI state information.
1064 newrtbm file is the realtime bitmap and is "new" for‐
1065 mat.
1066 prealloc file has preallocated data space after EOF.
1067 realtime file data is in the realtime subvolume.
1068 gen inode generation number.
1069 The following fields are in the u data fork union:
1070 bmbt bmap Btree root. This looks like a bmapbtd
1071 block with redundant information removed.
1072 bmx array of extent descriptors.
1073 dev dev_t for the block or character device.
1074 sfdir shortform (in-inode) version 1 directory.
1075 This consists of a hdr containing the parent
1076 inode number and a count of active entries in
1077 the directory, followed by an array list of
1078 hdr.count entries. Each such entry contains
1079 inumber, namelen, and name string.
1080 sfdir2 shortform (in-inode) version 2 directory.
1081 This consists of a hdr containing a count of
1082 active entries in the directory, an i8count
1083 of entries with inumbers that don't fit in a
1084 32-bit value, and the parent inode number,
1085 followed by an array list of hdr.count en‐
1086 tries. Each such entry contains namelen, a
1087 saved offset used when the directory is con‐
1088 verted to a larger form, a name string, and
1089 the inumber.
1090 symlink symbolic link string value.
1091 The following fields are in the a attribute fork union if it
1092 exists:
1093 bmbt bmap Btree root, as above.
1094 bmx array of extent descriptors.
1095 sfattr shortform (in-inode) attribute values. This
1096 consists of a hdr containing a totsize (total
1097 size in bytes) and a count of active entries,
1098 followed by an array list of hdr.count en‐
1099 tries. Each such entry contains namelen, val‐
1100 uelen, root flag, name, and value.
1101 log Log blocks contain the journal entries for XFS. It's not
1103 useful to examine these with xfs_db, use xfs_logprint(8) in‐
1104 stead.
1105 refcntbt There is one set of filesystem blocks forming the reference
1107 count Btree for each allocation group. The root block of this
1108 Btree is designated by the refcntroot field in the corre‐
1109 sponding AGF block. The blocks are linked to sibling left
1110 and right blocks at each level, as well as by pointers from
1111 parent to child blocks. Each block has the following fields:
1112 magic REFC block magic number, 0x52334643 ('R3FC').
1113 level level number of this block, 0 is a leaf.
1114 numrecs number of data entries in the block.
1115 leftsib left (logically lower) sibling block, 0 if
1116 none.
1117 rightsib right (logically higher) sibling block, 0 if
1118 none.
1119 recs [leaf blocks only] array of reference count
1120 records. Each record contains startblock,
1121 blockcount, and refcount.
1122 keys [non-leaf blocks only] array of key records.
1123 These are the first value of each block in
1124 the level below this one. Each record con‐
1125 tains startblock.
1126 ptrs [non-leaf blocks only] array of child block
1127 pointers. Each pointer is a block number
1128 within the allocation group to the next level
1129 in the Btree.
1130 rmapbt There is one set of filesystem blocks forming the reverse
1132 mapping Btree for each allocation group. The root block of
1133 this Btree is designated by the rmaproot field in the corre‐
1134 sponding AGF block. The blocks are linked to sibling left
1135 and right blocks at each level, as well as by pointers from
1136 parent to child blocks. Each block has the following fields:
1137 magic RMAP block magic number, 0x524d4233 ('RMB3').
1138 level level number of this block, 0 is a leaf.
1139 numrecs number of data entries in the block.
1140 leftsib left (logically lower) sibling block, 0 if
1141 none.
1142 rightsib right (logically higher) sibling block, 0 if
1143 none.
1144 recs [leaf blocks only] array of reference count
1145 records. Each record contains startblock,
1146 blockcount, owner, offset, attr_fork,
1147 bmbt_block, and unwritten.
1148 keys [non-leaf blocks only] array of double-key
1149 records. The first ("low") key contains the
1150 first value of each block in the level below
1151 this one. The second ("high") key contains
1152 the largest key that can be used to identify
1153 any record in the subtree. Each record con‐
1154 tains startblock, owner, offset, attr_fork,
1155 and bmbt_block.
1156 ptrs [non-leaf blocks only] array of child block
1157 pointers. Each pointer is a block number
1158 within the allocation group to the next level
1159 in the Btree.
1160 rtbitmap If the filesystem has a realtime subvolume, then the rbmino
1162 field in the superblock refers to a file that contains the
1163 realtime bitmap. Each bit in the bitmap file controls the
1164 allocation of a single realtime extent (set == free). The
1165 bitmap is processed in 32-bit words, the LSB of a word is
1166 used for the first extent controlled by that bitmap word. The
1167 atime field of the realtime bitmap inode contains a counter
1168 that is used to control where the next new realtime file will
1169 start.
1170 rtsummary If the filesystem has a realtime subvolume, then the rsumino
1172 field in the superblock refers to a file that contains the
1173 realtime summary data. The summary file contains a two-dimen‐
1174 sional array of 16-bit values. Each value counts the number
1175 of free extent runs (consecutive free realtime extents) of a
1176 given range of sizes that starts in a given bitmap block.
1177 The size ranges are binary buckets (low size in the bucket is
1178 a power of 2). There are as many size ranges as are neces‐
1179 sary given the size of the realtime subvolume. The first di‐
1180 mension is the size range, the second dimension is the start‐
1181 ing bitmap block number (adjacent entries are for the same
1182 size, adjacent bitmap blocks).
1183 sb There is one sb (superblock) structure per allocation group.
1185 It is the first disk block in the allocation group. Only the
1186 first one (block 0 of the filesystem) is actually used; the
1187 other blocks are redundant information for xfs_repair(8) to
1188 use if the first superblock is damaged. Fields defined:
1189 magicnum superblock magic number, 0x58465342 ('XFSB').
1190 blocksize filesystem block size in bytes.
1191 dblocks number of filesystem blocks present in the
1192 data subvolume.
1193 rblocks number of filesystem blocks present in the
1194 realtime subvolume.
1195 rextents number of realtime extents that rblocks con‐
1196 tain.
1197 uuid unique identifier of the filesystem.
1198 logstart starting filesystem block number of the log
1199 (journal). If this value is 0 the log is
1200 "external".
1201 rootino root inode number.
1202 rbmino realtime bitmap inode number.
1203 rsumino realtime summary data inode number.
1204 rextsize realtime extent size in filesystem blocks.
1205 agblocks size of an allocation group in filesystem
1206 blocks.
1207 agcount number of allocation groups.
1208 rbmblocks number of realtime bitmap blocks.
1209 logblocks number of log blocks (filesystem blocks).
1210 versionnum filesystem version information. This value
1211 is currently 1, 2, 3, or 4 in the low 4 bits.
1212 If the low bits are 4 then the other bits
1213 have additional meanings. 1 is the original
1214 value. 2 means that attributes were used. 3
1215 means that version 2 inodes (large link
1216 counts) were used. 4 is the bitmask version
1217 of the version number. In this case, the
1218 other bits are used as flags (0x0010: at‐
1219 tributes were used, 0x0020: version 2 inodes
1220 were used, 0x0040: quotas were used, 0x0080:
1221 inode cluster alignment is in force, 0x0100:
1222 data stripe alignment is in force, 0x0200:
1223 the shared_vn field is used, 0x1000: unwrit‐
1224 ten extent tracking is on, 0x2000: version 2
1225 directories are in use).
1226 sectsize sector size in bytes, currently always 512.
1227 This is the size of the superblock and the
1228 other header blocks.
1229 inodesize inode size in bytes.
1230 inopblock number of inodes per filesystem block.
1231 fname obsolete, filesystem name.
1232 fpack obsolete, filesystem pack name.
1233 blocklog log2 of blocksize.
1234 sectlog log2 of sectsize.
1235 inodelog log2 of inodesize.
1236 inopblog log2 of inopblock.
1237 agblklog log2 of agblocks (rounded up).
1238 rextslog log2 of rextents.
1239 inprogress mkfs.xfs(8) or xfs_copy(8) aborted before
1240 completing this filesystem.
1241 imax_pct maximum percentage of filesystem space used
1242 for inode blocks.
1243 icount number of allocated inodes.
1244 ifree number of allocated inodes that are not in
1245 use.
1246 fdblocks number of free data blocks.
1247 frextents number of free realtime extents.
1248 uquotino user quota inode number.
1249 pquotino project quota inode number; this is currently
1250 unused.
1251 qflags quota status flags (0x01: user quota account‐
1252 ing is on, 0x02: user quota limits are en‐
1253 forced, 0x04: quotacheck has been run on user
1254 quotas, 0x08: project quota accounting is on,
1255 0x10: project quota limits are enforced,
1256 0x20: quotacheck has been run on project quo‐
1257 tas).
1258 flags random flags. 0x01: only read-only mounts are
1259 allowed.
1260 shared_vn shared version number (shared readonly
1261 filesystems).
1262 inoalignmt inode chunk alignment in filesystem blocks.
1263 unit stripe or RAID unit.
1264 width stripe or RAID width.
1265 dirblklog log2 of directory block size (filesystem
1266 blocks).
1267 symlink Symbolic link blocks are used only when the symbolic link
1269 value does not fit inside the inode. The block content is
1270 just the string value. Bytes past the logical end of the
1271 symbolic link value have arbitrary values.
1272 text User file blocks, and other blocks whose type is unknown,
1274 have this type for display purposes in xfs_db. The block
1275 data is displayed in two columns: Hexadecimal format and
1276 printable ASCII chars.
1277
1279 Many messages can come from the check (blockget) command. If the
1280 filesystem is completely corrupt, a core dump might be produced instead
1281 of the message
1282 device is not a valid filesystem
1283 If the filesystem is very large (has many files) then check might run
1285 out of memory. In this case the message
1286 out of memory
1287 is printed.
1288 The following is a description of the most likely problems and the as‐
1290 sociated messages. Most of the diagnostics produced are only meaning‐
1291 ful with an understanding of the structure of the filesystem.
1292 agf_freeblks n, counted m in ag a
1294 The freeblocks count in the allocation group header for alloca‐
1295 tion group a doesn't match the number of blocks counted free.
1296 agf_longest n, counted m in ag a
1298 The longest free extent in the allocation group header for allo‐
1299 cation group a doesn't match the longest free extent found in
1300 the allocation group.
1301 agi_count n, counted m in ag a
1303 The allocated inode count in the allocation group header for al‐
1304 location group a doesn't match the number of inodes counted in
1305 the allocation group.
1306 agi_freecount n, counted m in ag a
1308 The free inode count in the allocation group header for alloca‐
1309 tion group a doesn't match the number of inodes counted free in
1310 the allocation group.
1311 block a/b expected inum 0 got i
1313 The block number is specified as a pair (allocation group num‐
1314 ber, block in the allocation group). The block is used multiple
1315 times (shared), between multiple inodes. This message usually
1316 follows a message of the next type.
1317 block a/b expected type unknown got y
1319 The block is used multiple times (shared).
1320 block a/b type unknown not expected
1322
1324 mkfs.xfs(8), xfs_admin(8), xfs_copy(8), xfs_logprint(8), xfs_metad‐
1325 ump(8), xfs_ncheck(8), xfs_repair(8), mount(8), chmod(2), mknod(2),
1326 stat(2), xfs(5).
1327 xfs_db(8)